Anionic Thia-Fries Rearrangements of Electron-Rich Ferrocenes and

Article pubs.acs.org/Organometallics

Anionic Thia-Fries Rearrangements of Electron-Rich Ferrocenes and the Unanticipated Formation of Diferrocenyl Sulfate from 2‑(Trimethylsilyl)ferrocenyl Imidazolylsulfonate Georg Werner and Holger Butenschön* Institut für Organische Chemie, Leibniz Universität Hannover, Schneiderberg 1B, D-30167 Hannover, Germany S Supporting Information *

ABSTRACT: Upon ortho lithiation ferrocenyl triflate and 1,1′ferrocenediyl ditriflate undergo anionic thia-Fries rearrangements instead of triflate elimination. To differentiate between an ortho metalation and an ortho deprotonation, 2(trimethylsilyl)ferrocenyl triflate was shown to undergo an anionic thia-Fries rearrangement to 2-((trifluoromethyl)sulfonyl)ferrocenol (5) in 84% yield upon treatment with tetrabutylammonium fluoride. Metalation of the respective tributylstannyl derivative with butyllithium also led to 5 in 99% yield as the result of the anionic thia-Fries rearrangement. 2Methoxyferrocenyl triflate also underwent the rearrangement upon ortho deprotonation with lithium diisopropylamide in practically quantitative yield at low temperature. The electron-rich 2-(((trifluoromethyl)sulfonyl)oxy)ferrocenolate was generated from 2-(((trifluoromethyl)sulfonyl)oxy)ferrocenyl acetate. However, ortho deprotonation again afforded the anionic thia-Fries rearrangement product. These results clearly show that even very electron rich ferrocene derivatives undergo an anionic thia-Fries rearrangement instead of a triflate elimination. In an attempt to induce an elimination supported by steric crowding, 2,3,4-trimethylferrocenyl triflate was deprotonated, giving 3,4,5-trimethyl-2-((trifluoromethyl)sulfonyl)ferrocenol in quantitative yield as the result of an anionic thia-Fries rearrangement. As an alternative to the triflates ferrocenyl imidazolylsulfonate was tested as the starting material. While this compound could not be deprotonated, the corresponding 2-trimethylsilyl derivative reacted with tetrabutylammonium fluoride in a very unusual reaction to give diferrocenyl sulfate in almost quantitative yield.

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INTRODUCTION Arynes have been used as valuable reactive intermediates in organic synthesis for decades and continue to attract the interest of organic, theoretical, and physical chemists.1−6 While there are many methods for their generation,7 triflate elimination has proven to be the superior method for the last 20 years.8 Lloyd-Jones showed in 2003 that the anionic thiaFries rearrangement is an alternative reaction mode of aryl triflates under the same reaction conditions. The authors found that electron-rich aryl triflates undergo triflate elimination to form aryne intermediates, while electron-poor aryl triflates react in anionic thia-Fries rearrangements with formation of 2((trifluoromethyl)sulfonyl)phenols.9 In an attempt to generate (aryne)tricarbonylchromium complexes 1 and in accord with these observations, we found that (aryltriflate)tricarbonylchromium complexes 2, with the tricarbonylchromium group being electron withdrawing, undergo anionic thia-Fries rearrangements to complexes 3 under mild reaction conditions in high yields.10 In order to render the complexes less electron poor, one of the carbonyl ligands was exchanged by a triphenylphosphine ligand. Surprisingly, these complexes also underwent the anionic thia-Fries rearrangement (Scheme 1),11 although, on the basis of spectroscopic data as well as of pKa measurements of respective benzoic acid complexes, the dicarbonyl(triphenylphosphane)chromium moiety is consid© 2013 American Chemical Society

Scheme 1

ered to be electron releasing.12 We note recent publications of Shibata and co-workers, who observed anionic thia-Fries rearrangements at electron-rich heterocyclic triflates.13,14 As an inherently electron-rich aromatic compound, ferrocene was selected for the desired elimination. In contrast to our expectation, however, ferrocenyl triflate (4) as well as 1,1′ferrocenediyl ditriflate (6) underwent smooth single and double anionic thia-Fries rearrangements under mild reaction conditions, resulting in the formation of 5 and 7 in high yields, respectively. Remarkably, as an unprecedented case of interannular stereoinduction, the reaction of 6 exclusively Special Issue: Ferrocene - Beauty and Function Received: April 19, 2013 Published: June 19, 2013 5798

dx.doi.org/10.1021/om400339t | Organometallics 2013, 32, 5798−5809

Organometallics

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Scheme 2

Scheme 3

afforded the meso diastereomer 7; no racemic diastereomer 8 was detected (Scheme 2).15 In light of these results, the question was raised as to how far ferrocenes even more electron rich than 4 would undergo anionic thia-Fries rearrangements or, alternatively, triflate elimination. Here we report the syntheses of some new electron-rich ferrocenyl triflates and their respective reactions. In addition, the rearrangement of ferrocenyl triflate was investigated with respect to the difference between ortho deprotonation and ortho metalation, which has recently been reported to be crucial.16

in its NMR spectra, indicating a diastereoselective deprotonation of 9. Diastereoselective ortho lithiations of ferrocenes bearing an asymmetric substituent have been reported for a variety of directing groups.19 The diastereoselectivity of the lithiation of 9 is explained by the trans-anellation of the tetrahydropyrane ring and the chelated six-membered ring in the diastereomer 9-Li, while the alternative diastereomer would show a less stable cis-anellation with an axially substituted tetrahydropyran ring. Although we have not so far not obtained crystals suitable for a structure analysis, we assign the configuration as shown in 10 on this basis. Hydrolysis with HCl in ethanol/water at 25 °C and subsequent triflation at −78 °C gave the desired 11 in practically quantitative yield. While in the latter reaction pyridine was initially used as the base, sodium hydride proved to be superior, because the column chromatography for the removal of the base can be avoided. Upon treatment of 11 with tetrabutylammonium fluoride in acetonitrile at 25 °C, an immediate anionic thia-Fries rearrangement was observed, which gave 5 in 84% yield. In the presence of dienes such as 2,5-dimethylfuran and 1,3diphenylisobenzofuran no cycloadduct of a ferrocyne intermediate was obtained. Because of the existence of several reports of aryne formation by metalation16,20−25 and as an alternative to the generation of the anion from 11 by treatment with tetrabutylammonium fluoride, metalation of the ortho position was considered. For this, tetrahydropyranyl ether 9 was deprotonated in the ortho position as in the synthesis of 10 and quenched by addition of tributylchlorostannane. The stannylated intermediate 12 was diastereoselectively obtained in 95% yield. Hydrolysis and subsequent triflation afforded 13 in 99% yield. In contrast to

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RESULTS AND DISCUSSION Lloyd-Jones has shown that the metalation of 2-chloro-6bromophenyl triflate with butyllithium at −78 °C in THF results in the formation of 3-chlorobenzyne, which was quantitatively trapped as its cycloadduct with 2,5-diphenylisobenzofuran. In contrast, the ortho deprotonation of 2chlorophenyl triflate with lithium diisopropylamide (LDA) in THF at −78 °C afforded the anionic thia-Fries rearrangement product 2-chloro-6-((trifluoromethyl)sulfonyl)phenol in 80% yield.16 In order to test in how far ortho lithiation instead of ortho deprotonation of ferrocenyl triflate changed the reaction result, 2-(trimethylsilyl)ferrocenyl triflate (11) was prepared by ortho lithiation of tetrahydropyranyl ether 917,18 with butyllithium at −78 °C followed by addition of chlorotrimethylsilane, affording 10 in 95% yield (Scheme 3). Because the tetrahydropyranyl substituent in 10 has a stereogenic carbon atom in addition to planar chirality, the formation of diastereomers was expected. However, the material obtained did not show duplicated signals 5799


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Scheme 4

Scheme 5

Scheme 6

Scheme 7

the preceding experiments starting from ferrocenyl triflate15 (4) or silyl derivative 11, the tributylstannyl compound 13 undergoes a metal exchange to the respective lithio compound by treatment with butyllithium. On the basis of the report of Lloyd-Jones this was expected to undergo elimination to ferrocyne and subsequent cycloaddition with the present 2,5diphenylisobenzofuran (DPIBF).16 However, much to our surprise, the experiment resulted in an instantaneous anionic thia-Fries rearrangement, giving 5 in quantitative yield (Scheme 4). As an alternative approach, ferrocenyl triflate (4) was ortho-

metalated using a TMP-zincate (TMP = 2,2,6,6-tetramethylpiperidino) according to Uchiyama, who performed related elimination reactions followed by cycloaddition with DPIBF in quantitative yield starting from phenyl triflate.22,23 However, executing this reaction sequence starting from 4 also resulted in an anionic thia-Fries rearrangement with formation of 5 in 73% yield. These are the first cases of anionic thia-Fries rearrangements induced by ortho metalation instead of ortho deprotonation. 5800


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Scheme 8

(23) in 76% yield in addition to 12% of the disubstitution product 24 and some unreacted 22 (12%). Addition of 1 equiv of butyllithium to 23 at −78 °C in the presence of 3 equiv of 2,5-dimethylfuran caused an immediate color change from light yellow to deep red, and subsequent addition of another 1 equiv of butyllithium at −78 °C and 2 equiv of dimethyl sulfate at 25 °C followed by reflux of the mixture for 24 h afforded 20 in 85% yield, indicating that ferrocenolate 25 underwent an anionic thia-Fries rearrangement. The transformations of intermediates 19 and 25 to 20 clearly indicate that an excess of electron density in the ferrocene system does not prevent the anionic thia-Fries rearrangement from occurring. Obviously the desired triflate elimination is not favored, even in particularly electron rich ferrocenyl triflates such as 19 and 25, presumably for steric reasons. As an alternative, steric crowding was considered a factor in favoring the elimination over the rearrangement, 2,3,4-trimethylferrocenyl triflate (34) being an attractive starting material. Our synthesis of 34 (Scheme 8) starts from ferrocenecarboxylic acid (27), which was obtained in 90% yield by Breit et al. from ferrocene by lithiation with tert-butyllithium/potassium tert-butoxide (20/1) followed by carboxylation.28 Alternatively, and possibly more economically, ferrocenecarboxylic acid (27) was obtained from ferrocene by acetylation with acetyl chloride/AlCl3, giving 26 in 88% yield followed by a haloform reaction with NaOH/Br2 in dioxane/water at 5 °C, affording 27 in 95% yield. To achieve this, however, the reaction time given in the procedure (see the Experimental Section) has to be kept very precisely. 2-Methylferrocenecarboxylic acid29 (28) was obtained from 27 in 80% yield by ortho metalation using 2 equiv of sec-butyllithium followed by methylation with iodomethane.30 Repetition of this procedure afforded 2,5dimethylferrocenecarboxylic acid31 (29) in 60% yield. Borane− dimethyl sulfide was shown to be an efficient reagent for the deoxygenative reduction of a variety of ferrocene derivatives.32 Application of the procedure to the reduction of 29 gave 1,2,3trimethylferrocene (30) in 75% yield. Treatment of 30 with

As the anionic thia-Fries rearrangement took place with ferrocenyl triflates upon ortho deprotonation as well as upon ortho metalation, the question was raised as to how electron rich a ferrocenyl triflate can be to allow this reaction. With this question in mind, some electron-rich ferrocenyl triflates were prepared and tested for the rearrangement oras an alternativefor the elimination reaction. 2-Methoxyferrocenyl triflate (18) was considered an attractive candidate (Scheme 5). The synthesis started from methoxyferrocene (14),26 which was ortho-metalated with BuLi/tBuOK at −78 °C and quenched by addition of iodine to give 2-iodomethoxyferrocene (16) in 64% yield. This yield was improved by use of (tetrahydropyranyloxy)ferrocene (9) as the starting material.18 Here, the ortho metalation was achieved with butyllithium in diethyl ether at −78 °C within 2 h. Quenching with I2 afforded intermediate 15 in 86% yield. This intermediate was also obtained in quantitative yield from the stannylated derivative 12 upon treatment with I2. Final acetal hydrolysis followed by methylation gave 16 in 99% yield. Next, an acetoxy group replaced the iodo substituent by treatment of 16 with acetic acid in acetonitrile in the presence of cuprous oxide, giving 17 in 89% yield. Ester hydrolysis and subsequent triflation afforded the desired 2-methoxyferrocenyl triflate (18) in 99% yield. 17 and 18 are the first ferrocene-1,2-diol derivatives known. Treatment of the methoxy-substituted ferrocenyl triflate 18 with lithium diisopropylamide at −78 °C in the presence of 2,5dimethylfuran resulted in an immediate color change from light yellow to deep red. Addition of dimethyl sulfate after warming to 25 °C gave 1,2-dimethoxy-5-((trifluoromethyl)sulfonyl)ferrocene (20) in 99% yield as the result of an anionic thia-Fries rearrangement to 19 followed by methylation (Scheme 6). 20 was also obtained by a different route (Scheme 7): 1,2diiodoferrocene27 (21) was treated with acetic acid and cuprous oxide in acetonitrile to give 1,2-diacetoxyferrocene (22) in 88% yield. The subsequent reaction of 22 with 1 equiv of methyllithium at −78 °C followed by quenching with an excess of triflic anhydride afforded 2-acetoxyferrocenyl triflate 5801


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Scheme 9

Scheme 10

Scheme 11

mercury acetate followed by lithium chloride afforded the mercurated product 31, which was, however, obtained as a mixture with other more highly mercurated ferrocene derivatives, as indicated by mass spectrometry. Subsequent reaction of the mixture containing 31 with iodine gave 1-iodo2,3,4-trimethylferrocene (32) in 15% yield from 30. 32 was transformed into the acetate 33 in 89% yield by treatment with cuprous oxide in acetonitrile/acetic acid. Finally, hydrolysis of the acetate followed by treatment of the intermediate ferrocenol, which was not isolated, with triflic anhydride in methylene chloride/pyridine gave triflate 34 in 99% yield. Treatment of 34 with lithium diisopropylamide at −78 °C in the presence of anthracene as a trapping diene afforded, however, in an immediate reaction 3,4,5-trimethyl-2((trifluoromethyl)sulfonyl)ferrocenol (35) in 99% yield as the exclusive product. The new compounds 29−35 were fully characterized by their spectroscopic data and elemental analyses. As ferrocenyl triflates, even if they were particularly electron rich or sterically crowded, turned out to be less suited for the desired elimination reactions, we looked for alternatives. Very recently Novák et al. reported the use of 2-(trimethylsilyl)phenyl imidazolylsulfonate as an efficient alternative to the respective triflates for the genesis of arynes.33 To test if the respective ferrocene derivative underwent an anionic thia-Fries rearrangement, as the triflates do, or an elimination with ferrocyne formation, or if another type of reactivity prevailed,

we prepared ferrocenyl imidazolylsulfonate (37) by hydrolysis of ferrocenyl acetate (36) followed by treatment of the crude ferrocenol intermediate with N,N′-sulfonyldiimidazole (Scheme 9). 37 was obtained in 95% yield as a light yellow solid. However, when 37 was treated with lithium diisopropylamide in THF in the presence of 2,5-dimethylfuran, no reaction was observed, even at elevated temperature, and 37 was quantitatively recovered. This observation corresponds to an earlier experiment with ferrocenyl tosylate.34 Quenching with D2O did not result in a deuterium incorporation; only solvent deprotonation/deuteration was observed. Obviously 37 is less acidic than the solvents used (MeCN, THF). In another attempt to realize the desired elimination, the 2trimethylsilyl derivative 38 was prepared in 95% yield from the tetrahydropyranyl ether 10 by hydrolysis followed by treatment with sodium hydride/sulfonyldiimidazole. 38 was treated with tetrabutylammonium fluoride in acetonitrile at 25 °C for 3 h, and no reaction was observed. However, much to our surprise, after heating at reflux for 10 h an almost quantitative yield of the unknown diferrocenyl sulfate (39) was isolated (Scheme 10). 39 was characterized by its NMR, IR. and mass spectra. Although the reaction was carried out in the presence of 3 equiv of 1,3-diphenylisobenzofuran for trapping a ferrocyne intermediate, there is no evidence that the diene participated in the formation of 39. Replacement of tetrabutylammonium fluoride by cesium fluoride afforded 39 in 67% yield. 5802


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Scheme 12

with tetrabutylammonium fluoride. When tetrabutylammonium fluoride was stirred in THF at 25 °C for 12 h in the presence of 37, diferrocenyl sulfate (39) was indeed formed as the only product in addition to some unconsumed starting material, as indicated by NMR. This observation shows the possibility of the nucleophilic fluoride attack in the presence of trimethylsilyl groups and thus supports a mechanism along the lines of that in Scheme 12. In view of the very high yield of 39 the reaction between 38 and 44 has to be fast as compared to that of 38 with tetrabutylammonium fluoride; otherwise, 2-(trimethylsilyl)ferrocenol would be the main product. The reaction between 38 and fluoride deserves further investigation: for example, with respect to the question of why the ferrocenolate and not the imidazolyl anion acts as a leaving group. Remarkably, the corresponding reaction of imidazolylsulfonylbenzene with fluoride to give diphenyl sulfate has not been reported.33

The reaction is remarkable because of its very high yield, which is achieved in spite of a number of reaction steps which must be involved in order to explain the formation of 39: loss of two trimethylsilyl groups, loss of two imidazolyl substituents, loss of one sulfonyl group, and the coupling of one ferrocenyl and one ferrocenylsulfonyl building block. The reaction mechanism might start with a desilylation followed by the coupling process or, vice versa, start with the coupling process followed by the desilylation. A possible mechanism starting with a desilylation (Scheme 11) involves the strained ferrocenyl-anellated 1,2-oxathiete 2,2-dioxide 41 as the key reactive intermediate, which is formed by an intramolecular substitution reaction with anion 40 as the nucleophile and the imidazolyl anion as the leaving group. As a second step, which must be fast as compared to the formation of the reactive intermediate 41, we consider a nucleophilic attack of 38 at the sulfur atom of 41, resulting in 42. Subsequent desilylation with tetrabutylammonium fluoride, protonation by water, and nucleophilic substitution with water at the imidazolylsulfonyl group leads to the formation of 39 in addition to imidazolylsulfonic acid. The practically quantitative yield of 39 implies that the reaction between 41 and 38 takes place immediately after the formation of 41 so that half of the starting material is converted to 41 and the other half reacts with 41 with formation of 39. For the reaction of 42 to give 39, we assume water acts as the nucleophile. The dissociated imidazolyl anion is thought to be less nucleophilic, and no sulfonyldiimidazole was found. Imidazolylsulfonic acid, which should be formed as a side product from 42, has barely been mentioned in the literature.35,36 As an alternative, one might envisage a route involving a nucleophilic attack of fluoride at the sulfonyl group to afford intermediate 43 followed by dissociation of imidazolylsulfonyl fluoride and ferrocenolate 44, which might then attack 38 and substitute the imidazole substituent, leading to 45. Although there is no experimental evidence in this case, one might also consider residual water in the tetrabutylammonium fluoride solution to generate hydroxide as the active nucleophile. Subsequent desilylation then affords the final product 39 (Scheme 12). The experiment that shows if such a nucleophilic attack of fluoride in the presence of trimethylsilyl groups is possible is the reaction of nonsilylated imidazolylsulfonylferrocene (37)

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CONCLUSION We have disclosed the mostly high-yielding syntheses of a number of new ferrocene derivatives leading to ferrocenyl triflates as starting materials for anionic thia-Fries rearrangements. These were observed with electron-rich as well as with sterically crowded representatives to take place immediately at low temperature in high yields. No elimination reactions to ferrocyne derivatives were observed. While triflate elimination is the most prominent method for the generation of arynes, the analogy between benzoic aromatic systems and ferrocene derivatives obviously does not apply to this reaction. Presumably, the difference in ring strain between an aryne and a ferrocyne has to be regarded as the cause for this striking difference in reactivity. The alternatively envisaged reaction starting from the respective imidazolyl sulfonates did not lead to the desired elimination. Instead, treatment of the 2trimethylsilyl-substituted derivative 38 resulted in the unanticipated formation of diferrocenyl sulfate (39) in very high yield. Mechanistic considerations include the ferrocenyl anellated 1,2oxathiete 2,2-dioxide 41 as the reactive intermediate or, alternatively, a fluoride attack at the sulfonyl group in the presence of trimethylsilyl groups with formation of the intermediate ferrocenolate 44. A control experiment showed that the non-silylated imidazolylsulfonylferrocene (37) reacts with tetrabutylammonium fluoride with formation of diferro5803


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min at 25 °C. After addition of water (50 mL) the mixture was extracted with CH2Cl2 (3 × 50 mL). The collected organic layers were washed (3 × 20 mL) and dried over anhydrous MgSO4. After solvent removal at reduced pressure, the crude product was purified by column chromatography (30 × 3 cm, SiO2, PE/CH2Cl2 8/2). 2(Trimethylsilyl)ferrocenyl triflate (11; 2.17 g, 5.4 mmol, 99%) was isolated as a light yellow oil. 1 H NMR (400.1 MHz, CDCl3): δ 0.33 (s, 9H, CH3), 3.9 (dd, 1H, J(H,H) = 1.25 Hz, Cp-H), 4.17 (t, 1H, J(H,H) = 2.6 Hz, Cp-H), 4.29 (s, 5H, Cp′-H), 4.69 (s, 1H, Cp-H) ppm. 13C NMR (100 MHz, CDCl3, DEPT 90, BB): δ −0.2 (CH3), 63.1 (Cp), 65.3 (Cp), 66.7 (Cp), 69.4 (Cp), 70.5 (Cp′), 118.5 (q, 1J(C,F) = 320.4 Hz, CF3), 123.6 (CCpO) ppm. IR: ν̃ 2939 (m, Cp-H), 1429 (s), 1368 (w), 1205 (s), 1130 (s), 935 (s), 844 (s), 820 (s), 833 (s), 811 (s) cm−1. HRMS (ESI, acetonitrile): calcd for C14H17F3FeO3SSi 405.9969; found 405.9988. Anal. Calcd for C14H17F3FeO3SSi (406.27): C, 41.39; H, 4.22. Found: C, 41.31; H, 4.24. Tributyl[2-(tetrahydropyran-2-yloxy)ferrocenyl]stannane (12). At −78 °C butyllithium in hexane (2.5 M, 4.5 mL, 11.2 mmol) was added to tetrahydropyran-2-yloxyferrocene18 (9; 2.90 g, 10.2 mmol) in diethyl ether (50 mL). The reaction mixture was warmed to 25 °C and stirred for 2 h. Then the reaction mixture was cooled to −78 °C, and Bu3SnCl (3.2 mL, 11.2 mmol, 95% purity) was added. The mixture was stirred for 30 min at −78 °C and then for 30 min at 25 °C. After addition of water (50 mL) the mixture was extracted with PE (3 × 50 mL). The collected organic layers were washed with water (3 × 20 mL) and dried over anhydrous MgSO4. After solvent removal at reduced pressure, the crude product was purified by column chromatography (30 × 3 cm, SiO2, PE). Tributyl[2-(tetrahydropyran2-yloxy)ferrocenyl]stannane (12; 5.59 g, 9.7 mmol, 95%) was isolated as a red oil. 1 H NMR (400.1 MHz, CDCl3): δ 0.92 (t, 9H, 3J(H,H) = 7.2, CH3), 1.02−1.14 (m, 6H, butyl-CH2), 1.32−1.41 (m, 6H, butyl-CH2), 1.52− 1.87 (m, 12H, butyl-CH2, 3 tetrahydropyranyl-CH2), 3.62−3.71 (m, 2H, tetrahydropyranyl-CH2), 3.98 (t, 1H, J(H,H) = 2.6 Hz, Cp-H), 4.05−4.16 (m, 6H, Cp′-H, OCHO), 4.46−4.47 (m, 1H, Cp-H), 4.86− 4.87 (m, 1H, Cp-H) ppm. 13C NMR (100 MHz, CDCl3, DEPT 90, BB): δ 10.5 (SnCH2), 13.9 (CH3), 18.7 (OCH2CH2CH2), 25.6 (OCH2CH2), 27.6 (SnCH2CH2CH2), 29.4 (SnCH2CH2), 30.7 (OCH2CH2CH2CH2), 58.6 (OCH2), 61.8 (Cp), 65.2 (Cp), 67.9 (Cp), 68.3 (Cp), 68.8 (Cp′), 99.1 (OCO), 130.0 (CCpO) ppm. IR: ν̃ 2953 (s, Cp-H), 2924 (s, Cp-H), 2871 (m), 2852 (m), 1435 (s), 1316 (m), 1202 (m), 1113 (s), 1074 (m), 1037 (s), 1020 (s), 999 (s), 987 (m), 844 (m), 832 (s) cm−1. MS (70 eV): m/z (%) 576 (63) [M+], 519 (23) [M+ − Bu], 491 (51) [M+ − THP], 434 (85) [M+ − THP − Bu], 405 (15) [M+ − 3 Bu], 377 (10) [M+ − THP − 2 Bu], 320 (69) [M+ − THP − 3 Bu], 291 (11) [SnBu3+], 200 (39) [FcO+], 120 (16) [Sn+], 85 (100) [THP+], 56 (35) [Fe+]. HRMS: calcd for C 27 H 44 FeO 2 Sn 576.1713; found 576.1708. Anal. Calcd for C27H44FeO2Sn (575.18): C, 56.38; H, 7.71. Found: C, 54.88; H, 7.68. 2-(Tributylstannyl)ferrocenyl Triflate (13). Hydrochloric acid (3 M, 30 mL) was added to tributyl(2-(tetrahydropyran-2-yloxy)ferrocenyl)stannane (12; 1.20 g, 2.1 mmol) in ethanol (60 mL). After it was stirred for 1 h, the mixture was diluted with water (50 mL), CH2Cl2 (50 mL) was added, and the mixture was intensely stirred for 5 min. After phase separation the organic layer was collected with a syringe and filtered into a Schlenk flask through a P4 frit covered with a 5 cm thick layer of MgSO4. After solvent removal at reduced pressure the remaining solid was dissolved in CH2Cl2 (50 mL), and after addition of pyridine (0.8 mL, 10.0 mmol) the mixture was cooled to −78 °C. (F3CO2S)2O (0.42 mL, 2.5 mmol) was added with stirring, and the mixture was stirred for 30 min at −78 °C and then for 30 min at 25 °C. After addition of water (50 mL) the mixture was extracted with CH2Cl2 (3 × 50 mL). The collected organic layers were washed with water (3 × 20 mL) and dried over anhydrous MgSO4. After solvent removal at reduced pressure, the crude product was purified by column chromatography (30 × 3 cm, SiO2, PE/CH2Cl2 8/2). 2(Tributylstannyl)ferrocenyl triflate (13; 1.30 g, 2.1 mmol, 99%) was isolated as a light yellow oil.

cenyl sulfate (39), thus supporting the second mechanistic proposal. To our knowledge, such a reaction is new and is therefore the subject of our ongoing research directed to its mechanistic details and synthetic scope.

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EXPERIMENTAL SECTION

General Considerations. All operations involving air-sensitive compounds were performed under a nitrogen atmosphere using Schlenk techniques. Reaction vessels were heated at reduced pressure with a heat gun and flushed with nitrogen. This procedure was repeated three times. THF was distilled with sodium wire/ benzophenone under a nitrogen atmosphere. CH2Cl2 was distilled from CaCl2 under a nitrogen atmosphere, and the dried solvents were flushed with argon for 20 min. Petroleum ether (PE) and tertbutylmethyl ether (TBME) were dried over CaCl2 and distilled. Silica gel was evacuated and put under normal pressure with nitrogen three times. All chiral compounds were used in racemic form. 1H and 13C NMR: Bruker WP 200 (200.1, 50 MHz), AVS 400 (400.1, 100 MHz), DRX 500 spectrometers (500.1, 125 MHz), chemical shifts referenced to residual solvent signals as internal standards. Signal assignments in 13 C NMR spectra are based on DEPT measurements. 31P NMR: Bruker AVS 400 spectrometer (162 MHz); 30% aqueous solution of H3PO4 used as the external standard. Infrared spectra (IR): PerkinElmer FT 1710 spectrometer; intensities shown as br = broad, s = strong, m = medium, and w = weak. Mass spectra (MS): Finnegan AM 400 instrument; ionization potential 70 eV. High-resolution mass spectra (HRMS): VG-Autospec instrument (peak matching with perfluorokerosin; NBA matrix), Micromass LCT spectrometer with Lock Spray Unit (ESI). Combustion analyses: CHN Rapid instrument (Heraeus) with acetanilide as standard. Melting points (mp): Electrothermal IA 9200 instrument. Trimethyl[2-(tetrahydropyran-2-yloxy)ferrocenyl]silane (10). At −78 °C butyllithium in hexane (2.5 M, 2.5 mL, 6.2 mmol) was added to tetrahydropyran-2-yloxyferrocene18 (9; 1.62 g, 5.7 mmol) in diethyl ether (50 mL). After the mixture was stirred at −78 °C for 2 h, Me3SiCl (0.78 mL, 6.2 mmol) was added. The mixture was stirred for 30 min at −78 °C and then for 30 min at 25 °C. After addition of water (50 mL) the mixture was extracted with PE (3 × 50 mL). The collected organic layers were washed with water (3 × 20 mL) and dried over anhydrous MgSO4. After solvent removal at reduced pressure, the crude product was purified by column chromatography (30 × 3 cm, SiO2, PE). Trimethyl[2-(tetrahydropyran-2-yloxy)ferrocenyl]silane (10, 1.94 g, 5.4 mmol, 95%) was isolated as an orange oil. 1 H NMR (400.1 MHz, CDCl3): δ 0.28 (s, 9H, CH3), 1.55−1.89 (m, 8H, 4 CH2), 3.96 (t, 1H, J(H,H) = 2.5 Hz, Cp-H), 4.04−4.18 (m, 6H, Cp′-H, OCHO), 4.42−4.44 (m, 1H, Cp-H), 4.89 (t, 1H, J(H,H) = 2.4 Hz, Cp-H) ppm. 13C NMR (100 MHz, CDCl3, DEPT 90, BB): δ −0.1 (CH 3 ), 18.8 (OCH 2 CH 2 CH 2 ), 25.6 (OCH 2 CH 2 ), 30.8 (OCH2CH2CH2CH2), 56.3 (Cp), 59.2 (OCH2), 59.8 (Cp), 61.9 (Cp′), 64.6 (Cp), 67.2 (Cp), 99.1 (OCHO), 129.0 (CCpO) ppm. IR: ν̃ 3092 (w), 2948 (m, Cp-H), 1437 (s), 1412 (s), 1316 (m), 1241 (s), 1201 (w), 1111 (s), 1004 (s), 957 (s), 914 (m), 833 (s), 811 (s), cm−1. MS (70 eV): m/z (%) = 358 (52) [M+], 274 (100) [M+ − THP]. HRMS: calcd for C18H26FeO2Si 358.1051; found 358.1046. Anal. Calcd for C18H26FeO2Si (358.34): C, 60.33; H, 7.31. Found: C, 60.31; H, 7.32. 2-(Trimethylsilyl)ferrocenyl triflate (11). Hydrochloric acid (3 M, 30 mL) was added to trimethyl(2-(tetrahydropyran-2-yloxy)ferrocenyl)silane (10; 1.94 g, 5.4 mmol) in ethanol (60 mL). The mixture was stirred for 1 h and then diluted with water (50 mL). After addition of CH2Cl2 (50 mL) the mixture was intensely stirred for 5 min. After phase separation the organic layer was collected with a syringe and filtered into a Schlenk flask through a P4 frit covered with a 5 cm thick layer of MgSO4. After solvent removal at reduced pressure the remaining solid was dissolved in CH2Cl2 (50 mL), and after addition of pyridine (1.1 mL, 13.0 mmol) the mixture was cooled to −78 °C. (F3CO2S)2O (0.52 mL, 6.5 mmol) was added to the stirred mixture. Stirring was continued for 30 min at −78 °C and then for 30 5804


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(30 × 3 cm, SiO2, PE/TBME 7/3). 1-Iodo-2-methoxyferrocene (16; 1.19 g, 3.5 mmol, 99%) was isolated as a red oil. 1 H NMR (400.1 MHz, CDCl3): δ 3.72 (s, 3H, CH3), 3.94 (t, 1H, J(H,H) = 2.6 Hz, Cp-H), 4.07 (q, 1H, J(H,H) = 1.3 Hz, Cp-H), 4.16 (s, 1H, Cp-H), 4.19 (s, 5H, Cp′-H) ppm. 13C NMR (100 MHz, CDCl3, DEPT 90, BB): δ 51.8 (CH3), 58.4 (Cp), 62.5 (Cp), 68.6 (Cp), 71.4 (Cp′), 71.5 (Cp), 126.3 (COCH3) ppm. IR: ν̃ 3093 (m), 2928 (s, Cp-H), 2856 (s, Cp-H), 1483 (s), 1458 (s), 1416 (s), 1369 (m), 1250 (s), 1108 (m), 1071 (s), 1044 (s), 1020 (s), 975 (m), 947 (m), 908 (m), 872 (w), 816 (s) cm−1. Anal. Calcd for C11H11FeIO (341.96): C, 38.64; H, 3.24. Found: C, 38.61; H, 3.27. 2-Methoxyferrocenyl Acetate (17). Cu2O (0.61 g, 4.2 mmol) and acetic acid (0.63 mL, 0.60 g, 10.5 mmol) was added to 1-iodo-2methoxyferrocene (16; 1.19 g, 3.5 mmol) in acetonitrile (50 mL). The reaction mixture was heated at reflux for 3 h. After addition of water (50 mL) the mixture was extracted with ethyl acetate (3 × 50 mL). The collected organic layers were washed with water (3 × 20 mL) and dried over anhydrous MgSO4. After solvent removal at reduced pressure the crude product was purified by column chromatography (30 × 3 cm, SiO2, PE/TBME 3/7). 2-Methoxyferrocenyl acetate (17; 0.85 g, 3.1 mmol, 89%) was isolated as a red solid (mp 36 °C). 1 H NMR (400.1 MHz, CDCl3): δ 2.23 (s, 3H, CCH3), 3.65 (t, 1H, J(H,H) = 2.9 Hz, Cp-H), 3.69 (s, 3H, OCH3), 3.91 (q, 1H, J(H,H) = 1.5 Hz, Cp-H), 4.19 (q, 1H, J(H,H) = 1.4 Hz, Cp-H), 4.26 (s, 5H, Cp′-H) ppm. 13C NMR (100 MHz, CDCl3, DEPT 90, BB): δ 21.2 (CCH3), 49.7 (OCH3), 55.3 (Cp), 57.0 (Cp), 58.27 (Cp), 69.8 (Cp′), 105.1 (CCpOAc), 118.0 (CCpOCH3), 169.5 (CO) ppm. IR: ν̃ 3099 (w), 2940 (m Cp-H), 1755 (s), 1507 (s), 1451 (m), 1422 (m), 1369 (m), 1286 (m), 1202 (s), 1125 (s), 1027 (m), 892 (m) cm−1. MS (70 eV): m/z (%) = 274 (41) [M+], 231 (100) [M+ − Ac], 121 (25) [FeCp+], 56 (22) [Fe+]. HRMS: calcd for C13H14FeO3 274.0292; found 274.0291. Anal. Calcd for C13H14FeO3 (274.01): C, 56.97; H, 5.15. Found: C, 55.30; H, 5.22. 2-Methoxyferrocenyl triflate (18). Water (40 mL) was added to 2-methoxyferrocenyl acetate (17; 0.85 g, 3.1 mmol) in ethanol (60 mL), and the mixture was heated to 70 °C. Potassium hydroxide (0.87 g, 15.5 mmol) was added to the stirred mixture, which was stirred at 70 °C for 30 min. After the mixture was cooled to 25 °C, oxygen free 37% aqueous hydrochloric acid (ca. 4 mL) was added with pH control until pH 6, and after addition of CH2Cl2 (50 mL) the mixture was intensely stirred for 5 min. After phase separation the organic layer was collected with a syringe and filtered into a Schlenk flask through a P4 frit covered with a 5 cm thick layer of MgSO4. After solvent removal at reduced pressure the remaining solid was dissolved in CH2Cl2 (50 mL), and after addition of pyridine (1.2 mL, 15.5 mmol) the mixture was cooled to −78 °C. (F3CO2S)2O (0.62 mL, 3.7 mmol) was added with stirring. The mixture was stirred for 30 min at −78 °C and then for 30 min at 25 °C. After addition of water (50 mL) the mixture was extracted with ethyl acetate (3 × 50 mL). The collected organic layers were washed with water (3 × 20 mL) and dried over anhydrous MgSO4. After solvent removal at reduced pressure, the crude product was purified by column chromatography (30 × 3 cm, SiO2, PE/ CH2Cl2 8/2). 2-Methoxyferrocenyl triflate (18; 1.13 g, 3.1 mmol, 99%) was isolated as an orange solid (mp 38 °C). 1 H NMR (400.1 MHz, [D6]acetone): δ 3.77 (s, 3H, CH3), 3.83 (t, 1H, J(H,H) = 3.0 Hz, Cp-H), 4.23 [q, 1H, J(H,H) = 1.5 Hz, Cp-H), 4.39 (s, 5H, Cp′-H), 4.42 (q, 1H, J(H,H) = 1.4 Hz, Cp-H) ppm. 13C NMR (100 MHz, [D6]acetone, DEPT 90, BB): δ 51.1 (CH3), 56.6 (Cp), 57.3 (Cp), 58.9 (Cp), 71.4 (Cp′), 110.7 (COS), 119.5 (q, 1 J(C,F) = 320.2 Hz, CF3), 119.6 (COCH3) ppm. IR: ν̃ 3398 (w), 2954 (m Cp-H), 1772 (m), 1727 (m), 1514 (m), 1421 (s), 1212 (s), 1139 (s), 1110 (m), 1043 (m), 861 (m) cm−1. HRMS (ESI, acetonitrile): calcd for C12H11F3FeO4S 363.9680; found 363.9677. Anal. Calcd for C12H11F3FeO4S (364.12): C, 39.58; H, 3.04. Found: C, 39.60; H, 3.07. 2,3-Dimethoxy-1-((trifluoromethyl)sulfonyl)ferrocene (20). Method A. At −78 °C LDA in THF (prepared from 2.5 M butyllithium (0.12 mL, 0.3 mmol) in hexane and diisopropylamine (0.13 mL, 0.9 mmol) in THF (20 mL) at −78 °C) was added dropwise over 40 min to a solution of 2-methoxyferrocenyl triflate (18; 0.10 g, 0.3 mmol) and 2,5-dimethylfuran (0.09 g, 0.9 mmol) in THF

H NMR (400.1 MHz, CDCl3): δ 0.93 (t, 9H, J = 7.15 Hz, CH3), 1.04−1.72 (m, 18H, CH2), 3.82 (q, 1H, J(H,H) = 1.3 Hz, Cp-H), 4.17 (t, 1H, J(H,H) = 2.5 Hz, Cp-H), 4.25 (s, 5H, Cp′-H), 4.68 (s, 1H, CpH) ppm. 13C NMR (100 MHz, CDCl3, DEPT 90, BB): δ −10.7 (SnCH2), 13.8 (CH3), 27.5 (SnCH2CH2CH2), 29.2 (SnCH2CH2), 53.6 (Cp), 62.0 (Cp), 63.2 (Cp), 67.3 (Cp), 70.2 (Cp′), 118.6 (q, 1 J(C,F) = 320.8 Hz, CF3), 124.9 (COS) ppm. IR: ν̃ 2957 (m Cp-H), 2924 (m Cp-H), 2854 (m), 1464 (w), 1421 (m), 1315 (m), 1248 (m), 1209 (s), 1141 (s), 998 (s), 980 (m), 843 (m), cm−1. HRMS (ESI, acetonitrile): calcd for C23H35F3FeO3SSn 624.0630; found 624.0638. Anal. Calcd for C23H35F3FeO3SSn (623.12): C, 44.33; H, 5.66. Found: C, 44.61; H, 5.87. 2-(2-Iodoferrocenoxy)tetrahydropyran (15). Iodine (1.00 g, 3.9 mmol) was added to tributyl(2-(tetrahydropyran-2-yloxy)ferrocenyl)stannane (12; 2.00 g, 3.5 mmol) in CH2Cl2 (20 mL), and the mixture was stirred for 1 h. Na2S2O3 (0.55 g, 3.5 mmol) in water (10 mL) was added, and the reaction mixture was stirred for 10 min. After addition of water (50 mL) the mixture was extracted with PE (3 × 50 mL). The collected organic layers were washed with water (3 × 20 mL) and dried over anhydrous MgSO4. After solvent removal at reduced pressure, the crude product was purified by column chromatography (30 × 3 cm, SiO2, PE). 2-(2-Iodoferrocenoxy)tetrahydropyran (15; 1.44 g, 3.5 mmol, 100%) was isolated as a red solid melting around room temperature (25−35 °C). 1 H NMR (400.1 MHz, CDCl3): δ 1.61−2.04 (m, 6H, 3 CH2), 3.98 (t, 1H, J(H,H) = 2.7 Hz, Cp-H), 4.09−4.16 (m, 3H, Cp-H, CH2), 4.19 (s, 5H, Cp′-H), 4.32−4.33 (m, 1H, Cp-H), 4.87 (t, 1H, 3J(H,H) = 3.2 Hz, OCHO) ppm. 13C NMR (100 MHz, CDCl3, DEPT 90, BB): δ 18.9 (OCH2CH2CH2), 25.5 (OCH2CH2), 30.7 (OCH2CH2CH2CH2), 57.5 (OCH2), 62.5 (Cp), 63.5 (Cp), 68.4 (Cp), 71.5 (Cp′), 67.2 (Cp), 100.6 (OCHO), 122.8 (ICCO) ppm. IR: ν̃ 3093 (w), 2941 (m Cp-H), 2871 (m, Cp-H), 1456 (s), 1348 (m), 1247 (m), 1202 (m), 1112 (s), 1026 (s), 972 (s), 970 (s), 906 (s), 872 (m), 815 (s) cm−1. HRMS (ESI, acetonitrile): calcd for C15H17FeIO2 411.9623; found 326.8969 (M+ − tetrahydropyranyl). Anal. Calcd for C15H17FeIO2 (412.05): C, 43.72; H, 4.16. Found: C, 43.62; H, 4.18. 1-Iodo-2-methoxyferrocene (16). Method A. After addition of KOtBu (0.26 g, 2.3 mmol) to methoxyferrocene26 (14; 0.50 g, 2.3 mmol) in THF (250 mL) the mixture was cooled to −78 °C. Butyllithium in hexane (2.5 M, 0.9 mL, 2.3 mmol) was added with stirring. The mixture was stirred for 2 h at −78 °C, then I2 (1.16 g, 4.6 mmol) was added, and the reaction mixture was stirred for 30 min at −78 °C. After the temperature was raised to 25 °C and Na2S2O3 (0.47 g, 3.5 mmol) in water (10 mL) was added, the reaction mixture was stirred for 10 min. Water (50 mL) was added, and the mixture was extracted with TBME (3 × 50 mL). The collected organic layers were washed with water (3 × 20 mL) and dried over anhydrous MgSO4. After solvent removal at reduced pressure, the crude product was purified by column chromatography (30 × 3 cm, SiO2, PE/TBME 7/ 3). 1-Iodo-2-methoxyferrocene (16; 0.50 g, 1.5 mmol, 64%) was isolated as a red oil. Method B. Hydrochloric acid (3 M, 30 mL) was added to 2-(2iodoferrocenoxy)tetrahydropyran (15; 1.44 g, 3.5 mmol) in ethanol (60 mL). The mixture was stirred for 1 h and diluted with water (50 mL). CH2Cl2 (50 mL) was added, and the mixture was intensely stirred for 5 min. After phase separation the organic layer was collected with a syringe and filtered through a P4 frit covered with a 5 cm thick layer of MgSO4 into a Schlenk flask. After solvent removal at reduced pressure the remaining solid was dissolved in THF (50 mL). At 25 °C NaH (0.18 g, 6.0 mmol, 80% in mineral oil) was added. The solution was stirred for 1 h at 25 °C, resulting in a color change from light yellow to red. After addition of Me2SO4 (0.33 mL, 3.5 mmol) the mixture was heated at reflux for 24 h. Then 20% aqueous KOH (20 mL) was added at 25 °C, and the mixture was heated at reflux for 1 h in order to decompose residual Me2SO4. After addition of water (50 mL) the mixture was extracted with ethyl acetate (3 × 50 mL). The collected organic layers were washed with water (3 × 20 mL) and dried over anhydrous MgSO4. After solvent removal at reduced pressure the crude product was purified by column chromatography 1

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4.41−4.43 (m, 6H, Cp′-H, Cp-H) ppm. 13C NMR (100 MHz, [D6]acetone, DEPT 90, BB): δ 21.0 (CH3), 57.9 (Cp), 59.1 (Cp), 59.2 (Cp), 72.5 (Cp′), 111.2 (SOCCO), 111.5 (SOCCO), 119.5 (q, 1 J(C,F) = 320.1 Hz, CF3), 168.8 (CO) ppm. HRMS (ESI, acetonitrile): calcd for C13H11F3FeO5S 391.9629; found 391.9610. (II) 1,2-Ferrocendiyl ditriflate (24; 0.04 g, 0.07 mmol, 12%) was isolated as a light yellow oil. 1 H NMR (400.1 MHz, [D6]acetone): δ 4.56−4.57 (m, 1H, OCCHCH), 4.59 (s, 5H, Cp′-H), 4.79 (d, 2H, J(H,H) = 1.4 Hz, OCCH) ppm. 13C NMR (100 MHz, [D6]acetone, DEPT 90, BB): δ 59.7 (Cp), 60.1 (Cp), 73.9 (Cp′), 111.9 [OCCO], 119.4 (q, 1J(C,F) = 319.9 Hz, CF 3) ppm. HRMS (ESI, acetonitrile): calcd for C12H8F6FeO6S2 481.9016; found 481.9016. Ferrocenecarboxylic Acid (27).28 At 10 °C a solution of NaOH/ Br2 in water (prepared from 50 mL of water, NaOH (36.8 g, 920.0 mmol), and Br2 (14.1 mL, 275.8 mmol)) was added slowly to a solution of acetylferrocene37,38 (26; 21 g, 92.1 mmol) in dioxane/ water (1/1, 200 mL). During the reaction the temperature must not exceed 10 °C. If a precipitate is observed, dioxane has to be added (in general 3 × 20 mL). After addition the reaction mixture was stirred for 1 h. Na2S2O3 (7.90 g, 50.0 mmol) in water (10 mL) was added, and the reaction mixture was stirred for 10 min. After addition of water (50 mL) and acidification by addition of 20% aqueous HCl (until pH 6) the mixture was extracted with ethyl acetate (3 × 50 mL). The collected organic layers were washed with water (3 × 20 mL) and dried over anhydrous MgSO4. After the solvent removal ferrocenecarboxylic acid (27; 20.00 g, 87.5 mmol, 95%) was isolated as a red powder and identified by comparison of the analytical data with those published (1H NMR).28 2-Methylferrocenecarboxylic Acid (28)..28,39,40 At −78 °C secbutyllithium (1.6 M in cyclohexane, 16.4 mL, 26.2 mmol) was added over 10 min to ferrocenecarboxylic acid (27; 3.0 g, 13.1 mmol) in THF (140 mL). The suspension was stirred until the solid had redissolved (ca. 2 h). Iodomethane (1.86 g, 0.82 mL, 13.1 mmol) was added, and the solution was warmed slowly to 25 °C. After addition of water (50 mL) and acidification by addition of 20% aqueous HCl (until pH 6) the mixture was extracted with ethyl acetate (3 × 25 mL). The collected organic layers were washed with water (3 × 20 mL) and dried over anhydrous MgSO4. After solvent removal at reduced pressure, the crude product was purified by column chromatography (30 × 3 cm, SiO2, PE/TBME 3/7). 2-Methylferrocenecarboxylic acid (28; 2.56 g, 10.5 mmol, 80%) was isolated as a yellow solid, identified by comparison of its analytical data with those published (1H NMR).39,40 2,5-Dimethylferrocenecarboxylic Acid (29).31 At −78 °C secbutyllithium (1.6 M in cyclohexane, 13.2 mL, 21.0 mmol) was added over 10 min to 2-methylferrocenecarboxylic acid (28; 2.56 g, 10.5 mmol) in THF (140 mL). The resulting suspension was stirred until the solid was redissolved (about 2 h). Then iodomethane (1.49 g, 0.66 mL, 10.5 mmol) was added, and the solution was warmed slowly to 25 °C. After addition of water (50 mL) and acidification by addition of 20% aqueous HCl (until pH 6) the mixture was extracted with ethyl acetate (3 × 25 mL). The collected organic layers were washed with water (3 × 20 mL) and dried over anhydrous MgSO4. After solvent removal at reduced pressure, the crude product was purified by column chromatography (30 × 3 cm, SiO2, PE/TBME 3/7). 2,5Dimethylferrocenecarboxylic acid (29; 1.63 g, 6.3 mmol, 60%) was isolated as a yellow solid (mp 105 °C dec). 1 H NMR (200 MHz, CDCl3): δ 2.56 (s, 6H, CH3), 4.11 (s, 5H, Cp′-H), 4.25 (s, 2H, CHCCH3) ppm. 13C NMR (100 MHz, CDCl3): δ 15.5 (CH3), 67.7 (H3CC), 71.4 (Cp′), 72.0 (CHCCH), 87.8 (CCO2H), 180.4 (CO) ppm. IR: ν̃ 2589 (br, OH), 1671 (s, CO), 1435 (m), 1303 (m), 1257 (s), 1102 (m), 814 (m) cm−1. HRMS (ESI, acetonitrile): calcd for C13H14FeO2 258.0343; found: 258.0341. Anal. Calcd for C13H14FeO2 (258.01): C, 60.50; H, 5.47. Found: C, 60.55; H, 5.56. 1,2,3-Trimethylferrocene (30). BH3·SMe2 (0.98 g, 1.20 mL, 12.6 mmol) was added to 2,5-dimethylferrocenecarboxylic acid (29; 1.63 g, 6.3 mmol) in CH2Cl2 (20 mL). The reaction mixture was stirred at 25 °C for 78 h. After addition of water (50 mL) the mixture was extracted

(20 mL). The color changed from light yellow to deep red. After the temperature was raised to 25 °C, Me2SO4 (0.04 mL, 0.4 mmol) was added, and the mixture was heated at reflux for 24 h. Then 20% KOH (20 mL) in water was added at 25 °C and the mixture was heated at reflux for 1 h in order to decompose residual Me2SO4. After addition of water (50 mL) the mixture was extracted with ethyl acetate (3 × 10 mL). The collected organic layers were washed with water (3 × 20 mL) and dried over anhydrous MgSO4. After solvent removal at reduced pressure the crude product was purified by column chromatography (30 × 3 cm, SiO2, TBME). 2,3-Dimethoxy-1(trifluoromethylsulfonyl)ferrocene (20; 0.10 g, 0.3 mmol, 99%) was isolated as a red oil. Method B. At −78 °C butyllithium in hexane (2.5 M, 0.2 mL, 0.51 mmol) was added dropwise over 40 min to 2-(((trifluoromethyl)sulfonyl)oxy)ferrocenyl acetate (23; 0.10 g, 0.3 mmol) and 2,5dimethylfuran (0.075 g, 0.8 mmol) in THF (20 mL). The color changed from light yellow to deep red. After the temperature was raised to 25 °C, Me2SO4 (0.05 mL, 0.51 mmol) was added, and the mixture was heated at reflux for 24 h. Then 20% KOH (20 mL) in water was added at 25 °C and the mixture was heated at reflux for 1 h in order to eliminate unconsumed Me2SO4. After addition of water (50 mL) the mixture was extracted with ethyl acetate (3 × 10 mL). The collected organic layers were washed with water (3 × 20 mL) and dried over anhydrous MgSO4. After solvent removal at reduced pressure the crude product was purified by column chromatography (30 × 3 cm, SiO2, TBME). 2,3-Dimethoxy-1-(trifluoromethylsulfonyl)ferrocene (20; 0.10 g, 0.3 mmol, 99%) was isolated as a red oil. 1 H NMR (400.1 MHz, CDCl3): δ 3.71 (s, 3H, CH3) 3.92 (s, 3H, CH3) 4.28 (d, 1H, 3J(H,H) = 3.2 Hz, Cp-H), 4.33 (d, 1H, 3J(H,H) = 3.2 Hz, Cp-H), 4.58 (s, 5H, Cp′-H) ppm. 13C NMR (400.1 MHz, CDCl3, BB): δ 53.9 (CH3), 58.2 (CH3), 58.9 (Cp), 62.4 (Cp), 72.2 (Cp-S), 72.3 (Cp′), 114.9 (COCH3), 119.3 (COCH3), 119.4 (q, 1 J(C,F) = 325.5 Hz, CF3) ppm. HRMS (ESI, acetonitrile): calcd for C13H13F3FeO4S: 377.9836; found 377.9832. 1,2-Ferrocenediyl Diacetate (22). Cu2O (0.48 g, 3.4 mmol) and acetic acid (0.53 mL, 0.51 g, 8.4 mmol) was added to 1,2diiodoferrocene27 (21; 0.60 g, 1.4 mmol) in acetonitrile (50 mL), and the reaction mixture was heated at reflux for 3 h. After addition of water (50 mL) the mixture was extracted with ethyl acetate (3 × 50 mL). The collected organic layers were washed with water (3 × 20 mL) and dried over anhydrous MgSO4. After solvent removal at reduced pressure the crude product was purified by column chromatography (30 × 3 cm, SiO2, PE/TBME 3/7). 1,2-Ferrocenediyl acetate (22; 0.37 g, 1.2 mmol, 88%) was isolated as a red solid. 1 H NMR (400.1 MHz, CDCl3): δ 2.22 (s, 6H, CH3), 3.81 (t, 1H, 3 J(H,H) = 2.9 Hz, OCCHCH), 4.21 (s, 5H, Cp′-H), 4.34 (d, 2H, J(H,H) = 2.9 Hz, OCCH) ppm. 13C NMR (100 MHz, CDCl3, DEPT 90, BB): δ 21.2 (CH3), 57.4 (OCCH), 57.7 (OCCHCH), 70.8 (Cp′), 106.8 (OCCH), 168.9 (CO) ppm. IR: ν̃ 3074 (w), 1755 (s), 1480 (m), 1370 (m), 1203 (s), 1104 (m), 1029 (m), 1006 (m), 893 (m), 814 (m) cm−1. HRMS (ESI, acetonitrile): calcd for C14H14FeO4 302.0241; found 302.0232. Anal. Calcd for C14H14FeO4 (302.12): C, 55.66; H, 4.67. Found: C, 55.11; H, 4.69. 2-(Acetoxy)ferrocenyl Trifluoromethanesulfonate (23) and 1,2-Ferrocendiyl Bis(trifluoromethanesulfonate) (24). At −78 °C methyllithium in hexane (1.6 M, 0.4 mL, 0.6 mmol) was added to 1,2-ferrocenediyl diacetate (22; 0.19 g, 0.6 mmol) in diethyl ether (50 mL). The reaction mixture was stirred for 30 min. (F3CO2S)2O (0.2 mL, 0.8 mmol) was added to the stirred mixture. Stirring was continued for 30 min at −78 °C and then for 30 min at 25 °C. After addition of water (50 mL) the mixture was extracted with ethyl acetate (3 × 25 mL). The collected organic layers were washed with water (3 × 20 mL) and dried over anhydrous MgSO4. After solvent removal at reduced pressure, the crude product was purified by column chromatography (30 × 3 cm, SiO2, PE/CH2Cl2 8/2). (I) 2-(Acetoxy)ferrocenyl trifluoromethanesulfonate (23; 0.18 g, 0.46 mmol, 76%) was isolated as a light yellow oil. 1 H NMR (400.1 MHz, [D6]acetone): δ 2.24 (s, 3H, CH3), 4.02 (t, 1H, J(H,H) = 3.1 Hz, Cp-H), 4.26 (t, 1H, J(H,H) = 3.1 Hz, Cp-H), 5806


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with PE (3 × 25 mL). The collected organic layers were washed with water (3 × 20 mL) and dried over anhydrous MgSO4. After solvent removal at reduced pressure, the crude product was purified by column chromatography (30 × 3 cm, SiO2, PE). 1,2,3-Trimethylferrocene (30; 1.07 g, 4.7 mmol, 75%) was isolated as a yellow oil. 1 H NMR (400.1 MHz, CDCl3): δ 1.87 (s, 9H, 3 CH3), 3.94 (s, 7H, H3CCCH, Cp′-H) ppm. 13C NMR (100 MHz, CDCl3, DEPT 90, BB): δ 11.5 (1 CH3), 13.7 (2 CH3), 66.7 (H3CCCCCH3), 70.5 (Cp′), 82.9 (H3CCCCH), 83.1 (H3CCCCCH3) ppm. IR: ν̃ 3021 (w), 2920 (s, Cp-H), 2854 (Cp-H), 1465 (m), 1382 (m), 1105 (m), 1029 (m), 1025 (m), 893 (s) cm−1. MS (70 eV): m/z (%) 228 (100) [M+], 213 (8) [M+ − CH3], 163 (12) [M+ − Cp], 121 (18) [FeCp+], 56 (15) [Fe+]. HRMS: calcd for C13H16Fe: 228.0601; found 228.0599. Anal. Calcd for C13H16Fe (228.12): C, 68.45; H, 7.07. Found: C, 68.53; H, 7.10. 2,3,4-Trimethyl(chloromercury)ferrocene (31). Hg(OAc)2 (2.0 g, 6.3 mmol) in methanol (15 mL) was added to 1,2,3trimethylferrocene (30; 1.63 g, 6.3 mmol) in toluene (50 mL). The reaction mixture was stirred at 25 °C for 48 h. Then LiCl (0.3 g, 7.0 mmol) in ethanol/water (1/1, 10 mL) was added and the reaction mixture was stirred at 25 °C for 24 h. After addition of water (50 mL) the mixture was extracted with CH2Cl2 (3 × 25 mL). The collected organic layers were washed with water (3 × 20 mL) and dried over anhydrous MgSO4. After solvent removal at reduced pressure a mixture of the desired 2,3,4-trimethyl(chloromercurio)ferrocene (31) and higher mercurated compounds was isolated as a light yellow powder, which was used for the next reaction. The full characterization of 31 was not possible. A very small amount (5 mg) of 31 could be isolated as the remaining residue by washing of the crude mixture with PE (3 × 100 mL). After removal of PE at reduced pressure, 2,3,4trimethyl(chloromercury)ferrocene (31) was isolated as a yellow powder (mp 180 °C dec). 1 H NMR (400.1 MHz, CDCl3): δ 1.83 (s, 9H, 3 CH3), 4.04 (s, 5H, Cp′-H), 4.24 (s, 1H, CH) ppm. MS (70 eV): m/z (%) 464 (63) [M+], 227 (100) [M+ − HgCl], 121 (60) [FeCp+], 106 (41) [CpMe3+], 56 (40) [Fe+]. HRMS: calcd for C13H15ClFeHg: 463.9918; found 463.9914. Anal. Calcd for C13H15ClFeHg (463.15): C, 33.71; H, 3.26. Found: C, 33.76; H, 3.06. 1-Iodo-2,3,4-trimethylferrocene (32). Iodine (3.0 g, 11.8 mmol) was added to a mixture of 2,3,4-trimethyl(chloromercury)ferrocene (31) and higher mercurated compounds (vide supra) in CH2Cl2 (40 mL), and the reaction mixture was stirred for 1 h. Na2S2O3 (1.87 g, 12.0 mmol) in water (10 mL) was added, and the reaction mixture was stirred for 10 min. After addition of water (50 mL) the mixture was extracted with PE (3 × 50 mL). The collected organic layers were washed with water (3 × 20 mL) and dried over anhydrous MgSO4. After solvent removal at reduced pressure, the crude product was purified by column chromatography (30 × 3 cm, SiO2, PE). 1-Iodo2,3,4-trimethylferrocene (32; 0.33 g, 0.94 mmol, 15% over two steps from 30) was isolated as a yellow oil. 1 H NMR (400.1 MHz, [D6]acetone): δ 1.89 (s, 3H, CH3), 1.95 (s, 3H, CH3), 1.98 (s, 3H, CH3), 3.85 (s, 1H, CH), 3.91 (s, 5H, Cp′-H) ppm. 13C NMR (100 MHz, CDCl3, DEPT 90, BB): δ 9.3 (ICCHCCCH3), 10.9 (ICCCH3), 13.3 (ICCHCCH3), 45.2 (CI), 69.3 (Cp), 70.9 (ICCH), 72.6 (Cp′), 72.7 (Cp), 75.7 (Cp) ppm. IR: ν̃ 3086 (w), 2947 (s, Cp-H), 2908 (Cp-H), 1703 (m), 1464 (m), 1378 (m), 1340 (m), 1243 (m), 1102 (m), 1029 (s), 994 (s), 812 (s) cm−1. HRMS (ESI, acetonitrile): calcd for C13H15FeI 353.9568; found 353.9565. Anal. Calcd for C13H15FeI (354.01): C, 44.11; H, 4.27. Found: C, 43.53; H, 5.12. 2,3,4-Trimethylferrocenyl Acetate (33). Cu2O (0.16 g, 1.1 mmol) and acetic acid (0.16 mL, 0.17 g, 2.8 mmol) was added to 1iodo-2,3,4-trimethylferrocene (32; 0.33 g, 0.94 mmol) in acetonitrile (50 mL). The reaction mixture was heated at reflux for 3 h. After addition of water (50 mL) the mixture was extracted with ethyl acetate (3 × 50 mL). The collected organic layers were washed with water (3 × 20 mL) and dried over anhydrous MgSO4. After solvent removal at reduced pressure the crude product was purified by column chromatography (30 × 3 cm, SiO2, PE/TBME 7/3). 2,3,4-

Trimethylferrocenyl acetate (33; 0.24 g, 0.84 mmol, 89%) was isolated as a yellow oil. 1 H NMR (400.1 MHz, CDCl3): δ 1.88 (s, 3H, OCCHCCH3), 1.89 (s, 6H, OCCCH3, OCCCCH3), 2.19 (s, 3H, OCCH3), 3.95 (s, 5H, Cp′-H), 4.19 (s, 1H, OCCH) ppm. 13C NMR (100 MHz, CDCl3, DEPT 90, BB): δ 10.5 (OCCHCCH3), 11.2 (OCCCCH3), 13.0 (OCCCH3), 21.2 (OCCH3), 60.4 (OCCH), 71.4 (Cp′), 75.1 (Cp), 78.1 (Cp), 113.3 (O−C), 170.4 (CO) ppm (one of the Cp signals was not observed and is probably covered by another one). IR: ν̃ 2914 (m, Cp-H), 1753 (s), 1450 (m), 1368 (m), 1208 (s), 1029 (m), 937 (m) cm−1. MS (70 eV): m/z (%) 286 (49) [M+], 244 (100) [M+ − Ac], 121 (38) [FeCp+], 56 (10) [Fe+]. HRMS: calcd for C15H18FeO2 286.0656; found 286.0658. 2,3,4-Trimethylferrocenyl Triflate (34). At −78 °C methyllithium in hexane (1.6 M, 1.6 mL, 1.0 mmol) was added to a solution of 2,3,4-trimethylferrocenyl acetate (33; 0.24 g, 0.8 mmol) in Et2O (20 mL). The reaction mixture was stirred for 30 min at −78 °C. Then (trifluoromethyl)sulfonic acid anhydride (0.2 mL, 1.8 mmol) was added with stirring. The mixture was stirred for 30 min at −78 °C and then for 30 min at 25 °C. After addition of water (50 mL) the mixture was extracted with ethyl acetate (3 × 25 mL). The collected organic layers were washed with water (3 × 20 mL) and dried over anhydrous MgSO4. After solvent removal at reduced pressure, the crude product was purified by column chromatography (30 × 3 cm, SiO2, PE/ CH2Cl2 8/2). 2,3,4-Trimethylferrocenyl triflate (34; 0.31 g, 0.8 mmol, 99%) was isolated as a light yellow oil. 1 H NMR (400.1 MHz, CDCl3): δ 1.87 (s, 3H, OCCHCCH3), 1.89 (s, 3H, OCCCCH3), 2.04 (s, 3H, OCCCH3), 4.05 (s, 5H, Cp′-H), 4.38 (s, 1H, CH). 13C NMR (100 MHz, CDCl3, DEPT 90, BB): δ 10.4 (OCCHCCH3), 11.0 (OCCCCH3), 12.8 (OCCCH3), 59.9 (OCCH), 72.2 (Cp′), 75.3 (Cp), 77.4 (Cp), 78.9 (Cp), 118.0 (C−O), 118.6 (q, 1J(C,F) = 320.9 Hz, CF3) ppm. IR: ν̃ 2920 (m, Cp-H), 1418 (s), 1385 (m), 1368 (m), 1243 (m), 1203 (s), 1140 (s), 1106 (m), 1059 (m), 940 (s), cm−1. MS (70 eV): m/z (%) 376 (45) [M+], 244 (100) [M+ − SO2CF3], 121 (45) [FeCp+], 56 (14) [Fe+]. HRMS: calcd for C14H15F3FeO3S 376.0043; found 376.0041. Anal. Calcd for C14H15F3FeO3S (376.17): C, 44.70; H, 4.02. Found: C, 45.42; H, 4.29. 3,4,5-Trimethyl-2-((trifluoromethyl)sulfonyl)ferrocenol (35). At −78 °C lithium diisopropylamide in THF (prepared from 2.5 M butyllithium in hexane (0.16 mL, 0.4 mmol) and diisopropylamine (0.6 mL, 4.0 mmol) in THF (20 mL)) was added dropwise over 40 min to 2,3,4-trimethylferrocenyl triflate (34; 0.15 g, 0.4 mmol) in THF (10 mL). The color immediately changed from light yellow to deep red. After the temperature was raised to 0 °C and the mixture was acidified by addition of oxygen-free 10% aqueous HCl (until pH 6), CH2Cl2 (50 mL) was added, and the mixture was intensely stirred for 5 min. After phase separation the aqueous layer was extracted twice with CH2Cl2 (20 mL each). The collected organic layers were taken up with a syringe and filtered into a Schlenk flask through a P4 frit covered with a 5 cm thick layer of MgSO4. After solvent removal at reduced pressure 2,3,4-trimethyl-5-((trifluoromethyl)sulfonyl)ferrocenol (35) was obtained as an orange liquid (0.15 g, 0.4 mmol, 99%). 1 H NMR (500.1 MHz, CDCl3): δ 1.99 (s, 3H, HOCC(CH3)CCH3), 2.04 ([s, 3H, SCCCH3), 2.07 (s, 3H, HOCCCH3), 4.19 (s, 5H, Cp′-H), 5.24 (s, 1H, OH). 13C NMR (125 MHz, CDCl3, DEPT 90, BB): δ 9.9 (HOCCCH3), 10.6 (HOCC(CH3)CCH3), 11.2 (SCCCH3), 59.1 (Cp), 73.9 (Cp′), 75.9 (Cp), 79.7 (HOCCS), 82.6 (Cp), 119.6 (q, 1J(C,F) = 325.3 Hz, CF3), 121.2 (HOC) ppm. IR: ν̃ 3406 (br, OH), 2924 (m, Cp-H), 1493 (s), 1451 (s), 1401 (m), 1384 (m), 1257 (m), 1115 (s), 1021 (m), 1003 (s), 824 (m), 805 (m), 720 (m) cm−1. HRMS (ESI, acetonitrile): calcd for C14H15F3FeO3S 376.0043; found 376.0041. Anal. Calcd for C14H15F3FeO3S (376.17): C, 44.70; H, 4.02. Found: C, 44.83; H, 4.15. Ferrocenyl Imidazolylsulfonate (37). Water (40 mL) was added to ferrocenyl acetate (36,; 2.0 g, 8.2 mmol) in ethanol (60 mL), and the mixture was heated to 70 °C. Potassium hydroxide (2.3 g, 41.0 mmol) was added with stirring, and the mixture was stirred at 70 °C for 30 min. After the mixture was cooled to 25 °C, oxygen-free 37% aqueous HCl (ca. 6 mL) was added with pH control until pH 6. After 5807


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addition of CH2Cl2 (50 mL) the mixture was intensely stirred for 5 min. After phase separation the organic layer was collected with a syringe and filtered through a P4 frit covered with a 5 cm thick layer of MgSO4 into a Schlenk flask. After solvent removal at reduced pressure the remaining solid (ferrocenol) was dissolved in dry CH2Cl2 (50 mL), and after addition of NaH (0.4 g, 9.8 mmol (60% in mineral oil)) N,N′-sulfonyldiimidazole (2.0 g, 10.1 mmol) was added. The mixture was stirred at reflux for 18 h. After cooling and addition of water (50 mL) the mixture was extracted with ethyl acetate (3 × 50 mL). The collected organic layers were washed (3 × 20 mL) and dried over anhydrous MgSO4. After solvent removal at reduced pressure, the crude product was purified by column chromatography (30 × 3 cm, SiO2, petroleum ether/ethyl acetate 7/3). Ferrocenyl imidazolylsulfonate (37; 2.6 g, 7.8 mmol, 95%) was isolated as a light yellow solid (mp 145.3 °C). 1 H NMR (400.1 MHz, CDCl3): δ 3.96 (AA′BB′, 2H, ∑J(H,H) = 1.7 Hz, Cp-H), 4.15 (AA′BB′, 2H, Cp-H), 4.27 (s, 5H, Cp′-H), 7.12 (s, 1H, NCHCH), 7.20 (s, 1H, NCHCH), 7.70 (s, 1H, NCHN) ppm. 13 C NMR (100 MHz, CDCl3, DEPT 90, BB): δ 61.3 (Cp), 64.7 (Cp), 70.2 (Cp′), 117.3 (C−O), 118.5 (NCHCH), 131.2 (NCHCH), 137.8 (NCHN) ppm. IR: ν̃ 3132 (w), 3103 (m), 1525 (m), 1419 (s), 1401 (m), 1369 (w), 1259 (m), 1199 (s), 1158 (s), 1099 (m), 1064 (m), 1020 (m), 992(m), 922 (s), 844 (s), 827 (s), 721 (m), 644 (m), 628 (s) cm−1. MS (70 eV): m/z (%) 332 (91) [M+], 201 (77) [M+ − SO2Im], 186 (32) [Fe(Cp)2+], 147 (21) [OSO2Im+], 121 (100) [FeCp+], 56 (34) [Fe+]. HRMS: calcd for C13H12FeN2O3S 331.9918; found 331.9920. Treatment of 37 with Lithium Diisopropylamide in the Presence of 2,5-Dimethylfuran. At −78 °C LDA in THF (prepared from 2.5 M butyllithium (0.7 mL, 1.7 mmol) in hexane and diisopropylamine (0.3 mL, 1.8 mmol) in THF (20 mL)) was added dropwise over 40 min to ferrocenyl imidazolylsulfonate (37,;0.5 g, 1.5 mmol) in THF (20 mL) and 2,5-dimethylfuran (0.5 mL, 4.5 mmol). The mixture was stirred at −78 °C for 3 h and then at 5 °C for 12 h. Then the mixture was heated at reflux for 5 h. No reaction was observed; the starting material was quantitatively recovered. 2-(Trimethylsilyl)ferrocenyl Imidazolylsulfonate (38). Hydrochloric acid (3 M, 30 mL) was added to trimethyl(2-(tetrahydropyran2-yloxy)ferrocenyl)silane (10; 1.7 g, 4.6 mmol) in ethanol (30 mL). The mixture was stirred for 1 h and diluted with water (50 mL). After addition of CH2Cl2 (50 mL) the mixture was intensely stirred for 5 min. After phase separation the organic layer was collected with a syringe and filtered through a P4 frit covered with a 5 cm thick layer of MgSO4 into a Schlenk flask. After solvent removal at reduced pressure the remaining solid was dissolved in dry CH2Cl2 (50 mL), and after addition of NaH (0.3 g, 5.7 mmol (60% in mineral oil)) N,N′sulfonyldiimidazole (1.2 g, 5.7 mmol) was added. The mixture was stirred at reflux for 18 h. After addition of water (50 mL) the mixture was extracted with ethyl acetate (3 × 50 mL). The collected organic layers were washed with water (3 × 20 mL) and dried over anhydrous MgSO4. After solvent removal at reduced pressure, the crude product was purified by column chromatography (30 × 3 cm, SiO2, TBME/PE 1/1). 2-(Trimethylsilyl)ferrocenyl imidazolylsulfonate (38; 1.77 g, 4.4 mmol, 95%) was isolated as a light yellow oil. 1 H NMR (400.1 MHz, CDCl3): δ 0.33 (s, 9H, CH3), 3.8 (dd, 1H, J(H,H) = 1.6 Hz, Cp-H), 3.9 (dd, 1H, J(H,H) = 1.3 Hz, Cp-H), 4.07 (dd, 1H, J(H,H) = 2.6 Hz, Cp-H), 4.23 (s, 5H, Cp′-H), 7.16 (s, 1H, NCHCH), 7.26 (s, 1H, NCHCH), 7.79 (s, 1H, NCHN) ppm. 13C NMR (100 MHz, CDCl3, DEPT 90, BB): δ −0.1 (CH3), 62.7 (Cp), 65.7 (CSiMe3), 66.9 (Cp), 69.9 (Cp), 70.4 (Cp′), 118.5 (NCHCH), 122.2 (CCpO), 131.2 (NCHCH), 137.7 (NCHN) ppm. IR: ν̃ 3157 (w), 3090 (w), 2964 (w, Cp-H), 1524 (w), 1426 (s), 1394 (m), 1316 (m), 1249 (m), 1200 (s), 1154 (s), 1051 (m), 983 (m), 818 (s), 727 (m) cm−1. MS (70 eV): m/z (%) 404 (100) [M+], 273 (6) [M+ − SO2Im], 257 (19) [M+ − OSO2Im], 184 (16) [M+ − (TMS + OSO2Im)], 121 (42) [FeCp+], 73 (18) [SiMe3+], 56 (10) [Fe+]. HRMS: calcd for C16H20FeN2O3SSi 404.0313; found 404.0315. Diferrocenyl Sulfate (39). Method B. At 25 °C tetrabutylammonium fluoride (0.32 mL of a 1 M solution in THF, 0.33 mmol) was added to 2-(trimethylsilyl)ferrocenyl imidazolylsulfonate (38; 0.09 g,

0.22 mmol) and diphenylizobenzofuran (0.2 g, 0.74 mmol, added for trapping a ferrocyne intermediate) in acetonitrile. The mixture was stirred at 25 °C for 3 h. No reaction was observed. Then the mixture was heated at reflux for 10 h. After addition of water (50 mL) the mixture was extracted with ethyl acetate (3 × 50 mL). The collected organic layers were washed (3 × 20 mL) and dried over anhydrous MgSO4. After solvent removal at reduced pressure the crude product was purified by column chromatography (30 × 3 cm, SiO2, petroleum ether/ethyl acetate 7/3). Diferrocenyl sulfate (39; 0.05 g, 0.11 mmol, 97%) was isolated as a light yellow solid (mp 127.5 °C). Method B. At 25 °C cesium fluoride (0.05 g, 0.33 mmol) was added to 2-(trimethylsilyl)ferrocenyl imidazolylsulfonate (38; 0.09 g, 0.22 mmol) and diphenylizobenzofuran (0.2 g, 0.74 mmol, added to trap a ferrocyne intermediate) in acetonitrile. The mixture was stirred at 25 °C for 3 h. No reaction was observed. Then the mixture was heated at reflux for 10 h. After addition of water (50 mL) the mixture was extracted with ethyl acetate (3 × 50 mL). The collected organic layers were washed (3 × 20 mL) and dried over anhydrous MgSO4. After solvent removal at reduced pressure the crude product was purified by column chromatography (30 × 3 cm, SiO2, petroleum ether/ethyl acetate 7/3), giving diferrocenyl sulfate (39; 0.034 g, 0.07 mmol, 67%). Control Experiment. At 25 °C tetrabutylammonium fluoride (0.1 mL of a 1 M solution in THF, 0.1 mmol) was added to ferrocenyl imidazolylsulfonate (36; 0.05 g, 0.15 mmol) in THF. The mixture was stirred at 25 °C for 12 h. After addition of water (25 mL) the mixture was extracted with ethyl acetate (3 × 25 mL). The collected organic layers were washed with water (3 × 10 mL) and dried over anhydrous MgSO4, and the solvent was removed at reduced pressure. The crude 1 H NMR depicted a 1/1 ratio of the starting material ferrocenyl imidazolylsulfonate (37) and diferrocenyl sulfate (39). 1 H NMR (400.1 MHz, CDCl3): δ 4.02 (AA′BB′, 2H, ∑J(H,H) = 1.8 Hz, Cp-H), 4.29 (s, 5H, Cp′-H), 4.49 (AA′BB′, 2H, Cp-H) ppm. 13 C NMR (100 MHz, CDCl3, DEPT 90, BB): δ 61.0 (CCpH), 63.9 (CCpH), 70.2 (Cp′), 118.5 (CCpO) ppm. IR: ν̃ 3100 (w), 2923 (m, Cp-H), 1434 (s), 1413 (s), 1346 (m), 1214 (m), 1192 (s), 1104 (m), 1023 (m), 999 (m), 925 (s), 870 (s), 814 (s), 795 (s), 738 (m) cm−1. MS (70 eV): m/z (%) 466 (27) [M+], 322 (100) [SO(OFeCp)2+], 201 (47) [FcO+], 186 (17) [Fe(Cp)2+], 121 (79) [FeCp+], 95 (7) [SO4+], 79 (6) [SO3+], 56 (18) [Fe+]. HRMS: calcd for C20H18Fe2O4S 465.9625; found 465.9624.

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ASSOCIATED CONTENT

S Supporting Information *

Figures giving 1H and 13C NMR spectra of all new compounds. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail for H.B.: [email protected]. de. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Support of this work by the Deutsche Forschungsgemeinschaft (DFG grant BU 814/16-1) is gratefully acknowledged. REFERENCES

(1) Hoffmann, R. W. Dehydrobenzene and Cycloalkynes; Academic Press: New York, 1967. (2) Wenk, H. H.; Winkler, M.; Sander, W. Angew. Chem. 2003, 115, 518; Angew. Chem., Int. Ed. 2003, 42, 502−527. (3) Jiao, H.; Schleyer, P. v. R.; Beno, B. R.; Houk, K. H.; Warmuth, R. Angew. Chem. 1997, 109, 2929; Angew. Chem., Int. Ed. Engl. 1997, 36, 2761. 5808


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(4) Warmuth, R. Angew. Chem. 1997, 109, 1406; Angew. Chem., Int. Ed. Engl. 1997, 36, 1347. (5) Sanz, R. Org. Prep. Proced. Int. 2008, 40, 215. (6) Pellissier, H.; Santelli, M. Tetrahedron 2003, 59, 701. (7) Dyke, A. M.; Hester, A. J.; Lloyd-Jones, G. C. Synthesis 2006, 4093. (8) Matsumoto, T.; Hosoya, T.; Katsuki, M.; Suzuki, K. Tetrahedron Lett. 1991, 32, 6735. (9) Charmant, J. P. H.; Dyke, A. M.; Lloyd-Jones, G. C. Chem. Commun. 2003, 380. (10) Zhao, Z.; Messinger, J.; Schön, U.; Wartchow, R.; Butenschön, H. Chem. Commun. 2006, 3007. (11) Werner, G.; Butenschön, H. Eur. J. Org. Chem. 2012, 3132. (12) Jaouen, G.; Dabard, R. J. Organomet. Chem. 1974, 72, 377. (13) Xu, X.-H.; Wang, X.; Liu, G.-k.; Tokunaga, E.; Shibata, N. Org. Lett. 2012, 14, 2544. (14) Xu, X.-H.; Taniguchi, M.; Azuma, A.; Liu, G. K.; Tokunaga, E.; Shibata, N. Org. Lett. 2013, 15, 686. (15) Werner, G.; Lehmann, C. W.; Butenschön, H. Adv. Synth. Catal. 2010, 352, 1345. (16) Dyke, A. M.; Gill, D. M.; Harvey, J. N.; Hester, A. J.; LloydJones, G. C.; Munoz, M. P.; Shepperson, I. R. Angew. Chem. 2008, 120, 5145; Angew. Chem., Int. Ed. 2008, 47, 5067. (17) Epton, R.; Marr, G.; Rogers, G. K. J. Organomet. Chem. 1976, 110, C42. (18) Epton, R.; Marr, G.; Rogers, G. K. J. Organomet. Chem. 1978, 150, 93. (19) Mamane, V. Tetrahedron: Asymmetry 2010, 21, 1019. (20) Lin, W.; Sapountzis, I.; Knochel, P. Angew. Chem. 2005, 117, 4330; Angew. Chem., Int. Ed. 2005, 44, 4258. (21) Sapountzis, I.; Lin, W.; Fischer, M.; Knochel, P. Angew. Chem. 2004, 116, 4464; Angew. Chem., Int. Ed. 2004, 43, 4364. (22) Uchiyama, M.; Miyoshi, T.; Kajihara, Y.; Sakamoto, T.; Otani, Y.; Ohwada, T.; Kondo, Y. J. Am. Chem. Soc. 2002, 124, 8514. (23) Uchiyama, M.; Kobayashi, Y.; Furuyama, T.; Nakamura, S.; Kajihara, Y.; Miyoshi, T.; Sakamoto, T.; Kondo, Y.; Morokuma, K. J. Am. Chem. Soc. 2008, 130, 472. (24) Harada, T.; Chiba, M.; Oku, A. J. Org. Chem. 1999, 64, 8210. (25) Hamura, T.; Ibusuki, Y.; Uekusa, H.; Matsumoto, T.; Siegel, J. S.; Baldridge, K. K.; Suzuki, K. J. Am. Chem. Soc. 2006, 128, 10032. (26) Nesmeyanov, A. N.; Sazonova, V. A.; Drosd, V. N. Chem. Ber. 1960, 93, 2717. (27) Roling, P. V.; Rausch, M. D. J. Org. Chem. 1974, 39, 1420. (28) Breit, B.; Breuninger, D. Synthesis 2005, 2782. (29) Hauser, C. R.; Lindsay, J. K.; Lednicer, D.; Cain, C. E. J. Org. Chem. 1957, 22, 717. (30) Nguyen, T.-H.; Castanet, A.-S.; Mortier, J. Org. Lett. 2006, 8, 765. (31) Kluser, E. Dissertation, Leibniz Universität Hannover, 2011. (32) Kim, D.-H.; Ryu, E.-S.; Cho, C. S.; Shim, S. C.; Kim, H.-S.; Kim, T.-J. Organometallics 2000, 19, 5784. (33) Kovács, S.; Csincsi, Á . I.; Nagy, T. Z.; Boros, S.; Timári, G.; Novák, Z. Org. Lett. 2012, 14, 2022. (34) Werner, G. Dissertation, Leibniz Universität Hannover, 2011. (35) Mayers, D. F.; Kaiser, E. T. J. Am. Chem. Soc. 1968, 90, 6192. (36) Dabkowski, W.; Michalski, J.; Skrzypczynski, Z. Chem. Ber. 1985, 118, 1809. (37) Weinmayr, V. J. Am. Chem. Soc. 1955, 77, 3009. (38) Graham, P. J.; Lindsey, R. V.; Parshall, G. W.; Peterson, M. L.; Whitman, G. M. J. Am. Chem. Soc. 1957, 79, 3416. (39) Kamikawa, K.; Fukumoto, K.; Yoshihara, K.; Furusyo, M.; Uemura, M.; Takemoto, S.; Matsuzaka, H. Chem. Commun. 2009, 1201. (40) Slocum, D. W.; Stonemark, F. E. J. Org. Chem. 1973, 38, 1677.

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