Efficient SN2 Fluorination of Primary and Secondary Alkyl Bromides by

Oct 18, 2013 - General Experimental Procedure and Reagent Availability .... by column chromatography on silica gel with pentane/AcOEt, 4:1 (v/v). ...
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Efficient SN2 Fluorination of Primary and Secondary Alkyl Bromides by Copper(I) Fluoride Complexes Yanpin Liu,† Chaohuang Chen,† Huaifeng Li,‡ Kuo-Wei Huang,*,‡ Jianwei Tan,† and Zhiqiang Weng*,† †

Department of Chemistry, Fuzhou University, Fujian 350108, China Division of Physical Sciences and Engineering and KAUST Catalysis Center, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia

‡

S Supporting Information *

ABSTRACT: Copper(I) fluoride complexes ligated by phenanthroline derivatives have been synthesized and structurally characterized by X-ray crystallography. These complexes adopt as either ionic or neutral forms in the solid state, depending on the steric bulkiness of the substituent groups on the phenanthroline ligands. These complexes react with primary and secondary alkyl bromides to produce the corresponding alkyl fluorides in modest to good yields. This new method is compatible with a variety of important functional groups such as ether, thioether, amide, nitrile, methoxyl, hydroxyl, ketone, ester, and heterocycle moieties.

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INTRODUCTION A large number of known biologically active molecules, including pharmaceuticals, agrochemicals, and positron-emission tomography (PET) imaging agents contain fluorine atoms.1−5 Conventionally, protocols for the incorporation of the fluorine atom into organic molecules include fluorination of aryl diazonium salts with HBF4 (Balz−Schiemann reaction),6 the direct fluorination of aromatic compounds, and the Halex exchange reaction of activated aryl halides with metal fluorides.7 More recently, the transition-metal-mediated C−F bond construction has emerged as an area of extensive research.8−10 Although a number of remarkable examples of such transformations incorporating Pd,11−19 Ni,20 Cu,21−23 and Ag24,25 as catalysts or mediators have been developed for the formation of aromatic C(sp2)−F bonds, the methods for general and site-specific formation of C(sp3)−F bonds still remain rather limited.26,27 Current efforts mainly focused on developing transitionmetal-catalyzed allylic fluorination28−31 and on the ringopening of epoxides.32 The existing methods for the synthesis of alkyl fluorides involve nucleophilic33,34 or electrophilic35 substitution reactions or radical fluorination.27,36,37 However, there are drawbacks with the use of fluoride ions with weak nucleophilicity such as KF or CsF for C(sp3)−F bond formation through direct nucleophilic substitution reactions. Relatively few examples have been reported involving metalmediated nucleophilic fluorination of benzyl and alkyl halides. Togni and co-workers reported the nucleophilic fluorination of benzylic and tert-butyl alkyl halides catalyzed by a ruthenium(II) complex using thallium fluoride.38 Sanford and co-workers reported a Pd-catalyzed method for the formation of aromatic and benzylic C−F bonds using electrophilic39 and then nucleophilic fluorinating reagents.40 The same group also reported the first example of highly selective C(sp3)−F bond © XXXX American Chemical Society

formation reductive elimination from palladium(IV) complexes.41 Lectka and co-workers published a polycomponent copper-catalyzed fluorination of aliphatic, benzylic, and allylic substrates with Selectfluor, the putative radical precursor Nhydroxyphthalimide (NHPI), and an anionic phase-transfer catalyst (KB(C6F5)4).42 Kim and co-workers demonstrated facile nucleophilic fluorination of some halo- and mesylalkanes to the corresponding fluoroalkanes using alkali metal fluorides in the presence of an ionic liquid and water or tert-alcohol.43−47 Most recently, Li and co-workers reported an efficient silvercatalyzed decarboxylative fluorination of aliphatic carboxylic acids with Selectfluor in aqueous solution.48 Groves and coworkers reported oxidative aliphatic and benzylic C−H fluorination with fluoride ion catalyzed by manganese.49 Even though the development of fluorination reactions has been greatly advanced, these approaches still suffer from limited substrate scopes and reaction conditions. The direct and convenient synthetic route for the fluorination of alkyl halides, especially secondary alkyl halides or mesylate,43,45 which could easily be eliminated to the corresponding alkene, is still challenging. Our continued efforts in the synthesis of a copper reagent for trifluoromethylation51−55 and trifluoromethylthiolation56−59 prompted us to develop a convenient and general method that would allow the preparation of alkyl fluorides from a common starting material. Herein, we report the synthesis of copper(I) fluoride complexes for efficient fluorination of primary and secondary alkyl bromides. Received: September 6, 2013

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RESULTS AND DISCUSSION

Synthesis of Copper(I) Fluoride Complexes. Formation of copper(I) complexes was achieved by the reaction of CuOtBu with the phenanthroline ligand in THF at rt, followed by the addition of (HF)3·NEt3, i.e., (Me2phen)2Cu(FHF) (1) and (tBu2Phen)Cu(F) (2) (Me2phen = neocuproine, t-Bu2Phen = 2,9-di-tert-butyl-1,10-phenanthroline), in 92% and 38% yields based on Cu, respectively. Scheme 1. Synthesis of Cu(l) Fluoride Complexes

Figure 2. ORTEP drawing of 2 showing 40% probability thermal ellipsoids. The (HF)3·NEt3 and hydrogen atoms are omitted for clarity.

adopts a trigonal planar geometry with one bidentate sp2 phen ligand and one fluoride coordinated to the copper(I) center. Notably, the two Cu−N bonds are not symmetrical, the bond distance of Cu(1)−N(1) (2.071(4) Å) being slightly longer than that of Cu(1)−N(2) (2.014(4) Å). In addition, the angle of N−Cu−N in 2 (84.1°) is larger than that found in 1. The Cu−F bond length (1.870(8) Å) in 2 is comparable to that of the (IPr)CuFHF (1.872 Å),60 but is slightly longer than that of (IMes)CuF (1.820 Å)63 and significantly shorter than that of (PPh3)3CuF (2.062(6) Å).62

These complexes exist as either ionic or neutral forms in the solid state, depending on the steric bulkiness of the substituent groups of the phenanthroline, similar to the observations by Leyssens and Riant et al. in (NHC)-copper(I) bifluoride complexes.60 Complex 1 was obtained as an orange-red solid, which is stable in air for several hours. Complex 2 was isolated as an orange, air- and moisture-sensitive solid. X-ray Structures of Complexes 1 and 2. The structures of 1 and 2 have been determined by single-crystal X-ray diffraction analysis. Their molecular structures are shown in Figures 1 and 2. The solid-state structure shows that 1 contains

Table 1. Selected Bond Lengths and Angles of Complex 1 Bond Lengths (Å) Cu(1)−N(1) Cu(1)−N(1A)

2.0418(7) Cu(1)−N(2) 2.0418(7) Cu(1)-N(2A) Bond Angles (deg)

N(1)−Cu(1)−N(2) N(1)−Cu(1)−N(1A) N(1)−Cu(1)−N(2A)

82.12(3) 122.69(4) 133.23(3)

N(1A)−Cu(1)−N(2A) N(2)−Cu(1)−N(2A) N(2)−Cu(1)−N(1A)

2.0565(6) 2.0564(6) 82.12(3) 110.33(3) 133.23(3)

Table 2. Selected Bond Lengths and Angles of Complex 2 Bond Lengths (Å) Cu(1)−F(1) Cu(1)−N(2)

1.870(8) Cu(1)−N(1) 2.014(4) Bond Angles (deg)

N(1)−Cu(1)−N(2) N(2)−Cu(1)−F(1) Cu(1)−N(2)−C(11) Cu(1)−N(2)−C(10)

Figure 1. ORTEP drawing of 1 showing 40% probability thermal ellipsoids. The hydrogen atoms are omitted for clarity.

84.07(16) 139.8(9) 109.4(3) 130.6(3)

N(1)−Cu(1)−F(1) Cu(1)−N(1)−C(12) Cu(1)−N(1)−C(1)

2.071(4)

135.8(9) 108.0(3) 131.6(4)

Reactivity of Complexes 1 and 2 with Alkyl Halides. Having established these solid-state structures, we sought to examine the reactivity of copper(I) complexes with alkyl bromides toward C(sp3)−F bond formation. Gratifyingly, treatment of 1 with 5 equiv of 3-phenylpropyl bromide (3a) in CH3CN at 110 °C for 15 h afforded (3-fluoropropyl)benzene (4a) in 92% yield (19F NMR, Table 3, entry 1) and allylbenzene as major side products. To our surprise, the neutral form of complex 2 led to poorer results in fluorination (Table 3, entry 2). Five control experiments were further carried out for the comparison of reactivity. KF alone showed very little activity (Table 3, entry 3), and alkyl bromide 3a was fully recovered when only (HF)3·

one cationic tetrahedral copper center ligated by two of the dative neocuproine ligands and one anionic [HF2]−, with the anion that carries the fluorine atoms not directly bonded with the Cu(I) center. Crystals of 2 (cocrystallizes with adventitious (HF)3·NEt3) suitable for X-ray diffraction were grown by recrystallization from its toluene solution layered with n-hexane. Complex 2 belongs to the rare examples of Cu(I) fluoride compounds containing a Cu−F bond,61 with the claim of the synthesis of several copper(I) fluoride being denied several times over the past hundred years.62 The solid-state structure of 2 shows a three-coordinate neutral [(phen)CuF] species. The complex B

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Table 3. Optimization of Fluorination of 4aa

Table 4. Substrate Scope of the Fluorination of Alkyl Bromidesa

entry

[F−] source

solvent

temp (°C)

time (h)

yield (%)b

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

1 2 KF (HF)3·NEt3 TBAF KF+(HF)3·NEt3 TBAF+(HF)3·NEt3 1 1 1 1 1 1 1 1

CH3CN CH3CN CH3CN CH3CN CH3CN CH3CN CH3CN THF diglyme DMF DMSO toluene CH2Cl2 MeOH CH3CN

110 110 110 110 110 110 110 110 110 110 110 110 40 80 110

15 15 15 15 15 15 15 15 15 15 15 15 15 15 8

92 21 6 0 27 1 25 9 33 46 5 trace 1 0.5 76

a

Reaction conditions: 1 (0.375 mmol), alkyl bromides 3 (0.250 mmol), 15 h, N2, 110 °C. Yields shown are of isolated products.

Conditions: [F−] sources (0.025 mmol), 3a (0.125 mmol), solvent (1.0 mL), under N2 atmosphere. bYields were determined by 19F NMR spectroscopy with PhOCF3 as internal standard. a

Table 5. Fluorination of Secondary Alkyl Bromidesa

NEt3 was used (Table 3, entry 4). On the other hand, tetrabutylammonium fluoride (TBAF) was found to mediate the fluorination but in low yield (Table 3, entry 5). Using a mixture of KF or TBAF with (HF)3·NEt3 did not improve the reaction yields (Table 3, entries 6, 7). The results are consistent with previous observations made by Chi and co-workers for fluorinations of mesylate with metal fluoride in polar aprotic solvents.44 It is important to note that changing the solvent has a profound effect on the reaction outcome. CH3CN was identified to be the most efficient. Replacement of CH3CN with THF, diglyme, or DMF led to lower conversions, as did the use of DMSO (Table 3, entries 8−11). The use of toluene, CH2Cl2, and MeOH suppresses the fluorination (Table 3, entries 12− 14). When the reaction time was shortened from 15 h to 8 h, a lower yield (76%) of 4a was observed (Table 3, entry 15). The substrate scope of this fluorination was then expanded with a series of examples (Table 4). Under the above optimized reaction conditions, the yields of the desired, isolated alkyl fluorides were obtained in a range of 50% to 90%, and many potentially reactive functional groups, such as phenoxide (4b), benzyl ether (4c), thioether (4d), amide (4e), nitrile (4h), hydroxyl (4i), and ester (4j, 4k), were well tolerated. The cases of 4i−4k were particularly noteworthy, as these results suggest that the base-sensitive groups do not influence the bromide substitution reaction. Unfunctionalized alkyl bromides also served as suitable substrates in this protocol (4f and 4g). Moreover, this method is compatible with more reactive electrophiles such as benzyl bromides, which can be readily fluorinated in good yields (4l−4o). Subsequently, we explored the reaction with the unactivated secondary alkyl bromides (Table 5). Under similar conditions, the reactions also proceeded successfully and gave the products in good to excellent yields (with alkenes as major byproducts; see Supporting Information). Fluorination of a secondary bromoalkane afforded the corresponding product in 74% yield (6a). This new protocol also provides good access to pharmaceutically important heterocycle-containing (e.g., indole

a

Reaction conditions: 1 (0.375 mmol), secondary alkyl bromides 5 (0.25 mmol), 15 h, N2, 110 °C. Yields shown are of isolated products.

and chromene) secondary alkyl bromides, which could be converted to the desired products (6b, 6c, and 6i) with synthetically useful yields (85%, 74%, and 89% yields, respectively). Notably, the fluorination is chemoselective. A variety of functional groups, including methoxyl (6d), ester (6e), ketone (6f), hydroxyl (6g), and amido groups (6h), were well tolerated to afford the desired products in 63−91% yields. It was worthwhile to note that sensitive functionalities such as a ketone (6f) or a hydroxyl (6g) group remained untouched under the same conditions, allowing further transformations. Of additional note, these moieties cannot survive in the presence of other fluorinating reagents, i.e., diethylaminosulfur trifluoride (DAST).64 To fully demonstrate the excellent chemoselectivity of our approach, substrates with aryl and alkyl sites were used for this reaction. Indeed, 5j smoothly underwent chemoselective fluorination with 1 at the C(sp3)−Br bond, leaving the C

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C(sp2)−Br bond available for further functionalization (Scheme 2).

Scheme 6. Inversion of Configuration

Scheme 2. Selective Fluorination of Alkyl over Aryl Bromides yield with the complete inversion of configuration.33 This finding strongly suggests that the fluorination proceeds through an SN2-type displacement of the bromide leaving group with the copper fluoride reagent.

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Having established the fluorination procedure, we turned our attention to explore this application to a more complex substrate. The vitamin E derivative 7 underwent fluorination with 1 smoothly to give the desired fluorinated product 8 in 86% yield (Scheme 3).

CONCLUSION In conclusion, we have developed an efficient and effective methodology to prepare alkyl fluorides directly from corresponding primary and secondary alkyl bromides by a copper(I) fluoride complex ligated by neocuproine. This ionic form of Cu(I) fluoride can be readily prepared, and it shows superior reactivity to those of neutral Cu(I) fluoride complexes. The reaction condition is mild, and a variety of useful functional groups including those not compatible with other existing methods, such as thioether, amide, nitrile, hydroxyl, and ester, can all be well tolerated. Our reagent should provide a convenient access to various alkyl fluorides that may find important applications in pharmaceutical and agrochemical industries.

Scheme 3. Fluorination of Vitamin E Derivative by Complex 1

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EXPERIMENTAL SECTION

General Experimental Procedure and Reagent Availability. All manipulations were carried out using a nitrogen-filled glovebox or standard Schlenk techniques under an inert atmosphere of nitrogen (purity ≥99.99%). All glassware was dried immediately prior to use. Solvents were freshly dried and degassed according to the procedures in Purification of Laboratory Chemicals prior to use. Deuterated solvents were purchased from Cambridge Isotope Laboratories, Inc., and were stored over activated 4 Å molecular sieves. 2,9-Di-tert-butyl1,10-phenanthroline50 was synthesized by a literature procedure. Unless otherwise noted, all other reagents and starting materials were purchased from commercial sources and used without further purification. The 1H, 19F, and 13C NMR spectra were obtained at 293 K on a Bruker Avance 400 spectrometer, and chemical shifts were recorded relative to the solvent resonance. GC-MS measurements were conducted on a Shimadzu QP2010SE. Elemental analyses were performed at Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences. Synthesis of [Cu(2,9-Dimethyl-1,10-phenanthroline)2] +[HF2]− (1). A solution of NaOt-Bu (20 mg, 0.21 mmol) in 2 mL of THF was added to a suspension of CuCl (20 mg, 0.20 mmol) in 6 mL of THF, and the resulting mixture was stirred at room temperature for 1 h. The resulting light yellow mixture was filtered through a layer of Celite. To this filtrate was added a solution of 2,9-dimethyl-1,10phenanthroline (42 mg, 0.20 mmol) in 4 mL of THF. The resulting solution turned reddish-brown immediately and was stirred at room temperature for an additional 5 min. A THF solution (1 mL) of (HF)3·NEt3 (32 mg, 0.20 mmol) was added dropwise, and the mixture was further stirred at room temperature for 5 min. The solution was filtered, and the filtrate was dried under vacuum to yield an orange solid. The resulting orange solid was washed with 2 × 2 mL of hexanes and dried under vacuum to obtain 48 mg (0.092 mmol, 92%) of 1. 1H NMR (400 MHz, DMSO-d6): δ 13.59 (s, 1H), 8.77 (d, J = 7.1 Hz, 4H), 8.23 (s, 4H), 7.98 (d, J = 7.2 Hz, 4H), 2.40 (s, 12H). 19F NMR (376 MHz, DMSO-d6): δ −158.4. 13C NMR (101 MHz, DMSO-d6): δ 158.2, 142.8, 138.0, 127.7, 126.5, 126.2, 25.7. MS (ESI): m/z = 479.1 [63CuL2+], 481.1 [65CuL2+]. Anal. Calcd for C28H27CuF2N4O: C 62.62, H 5.07, N 10.43. Found: C 62.05, H 4.83, N 10.37. Synthesis of (2,9-Di-tert-butyl-1,10-phenanthroline)CuF· ((HF)3NEt3) (2). A solution of NaOt-Bu (20 mg, 0.21 mmol) in 2

Additional experiments were conducted in an effort to gain insights for the plausible mechanism. To test the possibility that the fluorination may proceed via radical intermediates, the reaction of 1 and 3i was carried out in the presence of cyclohexa-1,4-diene (CHD), a radical scavenger. It was found that the addition of CHD did not have any pronounced effect on the reaction, and 4i was formed in the same yield both in the absence and in the presence (65%) of CHD (Scheme 4). Scheme 4. Radical Scavenger Experiments

When 1 reacted with 6-bromo-1-hexene in CD3CN at 110 °C for 15 h, 6-fluoro-1-hexene 9 was the only product in 99% yield detected by 19F NMR spectroscopy (Scheme 5). No cyclization Scheme 5. Fluorination of 6-Bromo-1-hexene

product, (fluoromethyl)cyclopentane 10, was observed. This absence of product 10 and the lack of any influence on the reactivity with the addition of a radical scavenger suggest that a radical mechanism is unlikely. Finally, the stereochemistry of the reaction with an enantiopure secondary tosylate (Scheme 6) was studied to probe the nature of the reaction mechanism. The reaction of 1 with 12, prepared from the corresponding chiral secondary alcohol 11, furnished the corresponding product 13 in 85% D

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to a dried 100 mL test tube with Teflon screw cap equipped with magnetic stir bar. The tube was sealed, and the solution was placed into a preheated 110 °C oil bath for 15 h. The tube was removed from the oil bath and allowed to cool. The reaction mixture was filtered through Celite to remove metal salts. Water (50 mL) was added to the mixture at 0 °C. The resulting mixture was extracted with CH2Cl2 (3 × 10 mL). The combined organic layers were washed with H2O (20 mL) and brine (20 mL) and dried over magnesium sulfate. The solvent was removed by rotary evaporation, and the resulting crude product was purified by column chromatography on silica gel with pentane/AcOEt, 4:1 (v/v). Crystal Structure Analyses. Suitable crystal of 1 and 2 were mounted on quartz fibers, and X-ray data collected on a Bruker AXS APEX diffractometer, equipped with a CCD detector at −50 °C, using Mo Kα radiation (λ 0.71073 Å). The data were corrected for Lorentz and polarization effects with the SMART suite of programs65 and for absorption effects with SADABS.66 Structure solution and refinement were carried out with the SHELXTL suite of programs.67 The structure was solved by direct methods to locate the heavy atoms, followed by difference maps for the light non-hydrogen atoms. In crystal 1, the asymmetric unit contains half a molecule of the cation C28H24N4Cu and one-half of the anion and solvent pair of HF2 and H2O. HF2 and H2O are disordered around the 2-fold axis. For the disordered HF2 and H2O, the H atoms were put at calculated positions, and restraints in anisotropic thermal parameters of the O were applied. In crystal 2, the asymmetric unit contains one molecule of C20H26N2CuF and one (HF)3·(NEt3). H atoms of the F were not located. One of the F atoms was disordered into two positions with an occupancy ratio of 80:20. In crystal 2′, CuHF2 was disordered into two positions with an occupancy ratio of 58:42.

mL of THF was added to a suspension of CuCl (20 mg, 0.20 mmol) in 6 mL of THF, and the resulting mixture was stirred at room temperature for 1 h. The resulting light yellow mixture was filtered through a layer of Celite. To this filtrate was added a solution of 2,9-ditert-butyl-1,10-phenanthroline (58 mg, 0.20 mmol) in 1 mL of THF. The resulting solution turned reddish-brown immediately and was stirred at room temperature for an additional 5 min. A THF solution (1 mL) of (HF)3·NEt3 (32 mg, 0.20 mmol) was added dropwise, and the mixture was further stirred at room temperature for 5 min. The solution was filtered, and the filtrate was dried under vacuum to yield an orange solid. The solid was dissolved in 5 mL of toluene, layered with 10 mL of hexanes. The resulting solution was then cooled at −10 °C for 48 h. The resulting orange crystals were separated from the supernatant, washed with 2 × 2 mL of hexanes, and dried under vacuum to obtain 29 mg (0.078 mmol, 38%) of 2. 1H NMR (400 MHz, DMSO-d6): δ 11.63 (s, 2H), 8.47 (s, 2H), 7.96 (s, 4H), 1.60 (s, 18H). 19F NMR (376 MHz, DMSO-d6): δ −148.2, −148.3. 13C NMR (101 MHz, DMSO-d6): δ 168.5, 129.3, 128.7, 127.1, 126.1, 119.9, 38.7, 30.6. MS (EI): m/z = 355 [M − F]. Anal. Calcd for C26H42CuF4N3: C 58.24, H 7.90, N 7.84. Found: C 58.65, H 7.56, N 7.75. General Procedure for Fluorination of Primary and Secondary Alkyl Bromides by Complex [Cu(2,9-dimethyl1,10-phenanthroline)2]+[HF2]− (1). Complex 1 (195 mg, 0.375 mmol), 0.25 mmol of primary or secondary alkyl bromides, and 10 mL of CH3CN were added to a dried 100 mL test tube with a Teflon screw cap equipped with magnetic stir bar. The tube was sealed, and the solution was placed into a preheated 110 °C oil bath for 15 h. The tube was removed from the oil bath and allowed to cool. The reaction mixture was filtered through Celite to remove metal salts. Water (20 mL) was added to the mixture at 0 °C. The resulting mixture was extracted with diethyl ether (3 × 10 mL). The combined organic layers were washed with H2O (1 × 20 mL) and brine (1 × 20 mL), and dried over magnesium sulfate. The solvent was removed by rotary evaporation in an ice bath, and the resulting crude product was purified by column chromatography on silica gel with pentane and diethyl ether. Procedure for the Reaction of 1 with 6-Bromohexan-1-ol (3i) without Cyclohexa-1,4-diene. 1 (13 mg, 0.025 mmol), 3i (22.6 mg, 0.125 mmol), and 1 mL of CH3CN were added to a dried 5 mL test tube with a Teflon screw cap equipped with a magnetic stir bar. The tube was sealed, and the solution was placed into a preheated 110 °C oil bath for 15 h. The tube was removed from the oil bath and allowed to cool; then 10 μL of (trifluoromethoxy)benzene was added as an internal standard. The resulting mixture was filtered through a layer of Celite, and the filtrate was analyzed by 19F NMR and GC-MS. The yield of 6-fluorohexan-1-ol (4i) was calculated to be 64%. Procedure for the Reaction of 1 with 6-Bromohexan-1-ol (3i) in the Presence of 1.0 equiv of CHD. 1 (13 mg, 0.025 mmol), 3i (22.6 mg, 0.125 mmol), CHD (2 mg, 0.025 mmol), and 1 mL of CH3CN were added to a dried 5 mL test tube with a Teflon screw cap equipped with a magnetic stir bar. The tube was sealed, and the solution was placed into a preheated 110 °C oil bath for 15 h. The tube was removed from the oil bath and allowed to cool; then 10 μL of (trifluoromethoxy)benzene was added as an internal standard. The resulting mixture was filtered through a layer of Celite, and the filtrate was analyzed by 19F NMR and GC-MS. The yield of 6-fluorohexan-1ol (4i) was calculated to be 65%. Procedure for Fluorination of 6-Bromo-1-hexene by 1. 1 (44 mg, 0.080 mmol), 6-bromohex-1-ene (8.2 mg, 0.050 mmol), and 1 mL of CD3CN were added to a dried 5 mL test tube with a Teflon screw cap equipped with a magnetic stir bar. The tube was sealed, and the solution was placed into a preheated 110 °C oil bath for 15 h. The tube was removed from the oil bath and allowed to cool. Then 10 μL (trifluoromethoxy)benzene was added as an internal standard. The resulting mixture was analyzed by 19F NMR and GC-MS. The yield of 6-fluorohex-1-ene (9) was calculated to be 99%. Formation of (fluoromethyl)cyclopentane product was not detected from 1H NMR. Procedure for Inversion of Configuration. 1 (390 mg, 0.75 mmol), 12 (200 mg, 0.50 mmol), and 25 mL of CH3CN were added

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ASSOCIATED CONTENT

S Supporting Information *

Spectra and crystallographic data (CIF). This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (Z.W.). *E-mail: [email protected] (K.-W.H.). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We acknowledge the financial support from National Natural Science Foundation of China (21072030), Research Fund for the Doctoral Program of Higher Education of China (No. 20123514110003), SRF for ROCS, SEM (J20121707), the Science Foundation of the Fujian Province, China (2013J01040), and Fuzhou University (022318, 022494) to Z.W. and King Abdullah University of Science and Technology to K.-W.H.

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REFERENCES

(1) Shimizu, M.; Hiyama, T. Angew. Chem., Int. Ed. 2005, 44, 214. (2) Kirk, K. L. Org. Process Res. Dev. 2008, 12, 305. (3) O’Hagan, D. Chem. Soc. Rev. 2008, 37, 308. (4) Purser, S.; Moore, P. R.; Swallow, S.; Gouverneur, V. Chem. Soc. Rev. 2008, 37, 320. (5) Littich, R.; Scott, P. J. H. Angew. Chem., Int. Ed. 2012, 51, 1106. (6) Balz, G.; Schiemann, G. Ber. Dtsch. Chem. Ges. 1927, 60, 1186. (7) Sun, H.; DiMagno, S. G. Angew. Chem., Int. Ed. 2006, 45, 2720. (8) Brown, J. M.; Gouverneur, V. Angew. Chem., Int. Ed. 2009, 48, 8610. (9) Grushin, V. V. Acc. Chem. Res. 2009, 43, 160. (10) Furuya, T.; Kamlet, A. S.; Ritter, T. Nature 2011, 473, 470.

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Organometallics

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dx.doi.org/10.1021/om4008967 | Organometallics XXXX, XXX, XXX−XXX