J. Org. C h e m . 1984,49, 203-205
Protecting Groups for the Pyrrole and Indole Nitrogen Atom. The [2-(Trimethy1silyl)ethoxylmet hyl Moiety. Lithiation of 1-[ [2-(Trimethylsilyl)ethoxy]methyl]pyrrole1~2
Table I. Synthesis and Cleavage of N - [ [ 2 4 Trimethylsily1)ethoxy]methyl ]pyrroles and Indole synthesis cleavage %
comud 3a
Joseph M. Muchowski* and Dennis R. Solas
(1)Contribution No. 648 from the Syntex Institute of Organic Chemistry. (2)Presented at the 66th Canadian Chemical Conference of the Chemical Institute of Canada, Calgary, Alberta, Canada, June 54,1983. (3) For a brief discussion of the pyrrole N-protecting groups now in use, see: Gonzalez, C.; Greenhouse, R.; Muchowski, J. M. Can.J . Chem. 1983,61,1697. (4)The (benzy1oxy)methylmoiety6 should also be utilizable in this context, but, to date, it has only been applied to the N-protection of acylated pyrroles. (5)Anderson, H.J.; Groves, J. K. Tetrahedron Lett. 1971, 3165. Groves, J. K.; Cundasawmy, N. E.; Anderson, H. J. Can.J. Chem. 1973, .51. - - , inm. - - -- . (6)Lipshutz, B. H.;Pegram, J. J. Tetrahedron Lett. 1980,21,3343. (7)After this work was completed, the synthesis and lithiation of SEM-protected pyrrole was described by: Edwards, M. P.; Ley, S. V.; Lister, S. G.; Palmer, B. D. J. Chem. SOC.,Chem. Commun.1983,630. (8) Purchased from Fluka Chemical Corp. (9)The cleavage of (trialkylsily1)oxygroups under these conditions has been described Kelly, D. R.; Roberts, S. M.; Newton, R. F. “Chemistry, Biochemistry and Pharmacological Activity of Prostanoids”;Roberts, S. M., Scheinmann, F., Eds.; Pergamon Press: Oxford, 1979;pp 365-9.
0022-3263/84/1949-0203$01.50/0
H CHO
3c 3d 3g 6
Received J u n e 28, 1983
yield 85 98
R
3b
S y n t e x Research, I n s t i t u t e of Organic Chemistry, P a l o Alto, California 94304
The protecting groups currently available for the pyrrole nitrogen atom are considerable in n ~ m b e r . Very ~ few of these, however, can be used for pyrroles not stabilized by electron-attracting substituents, because the conditions required for the removal of the N-protecting group are too vigorous to permit the survival of the pyrrole nucleus. The utilization of the 2-chloroethyl group for the protection of the pyrrole nitrogen atom was recently de~cribed.~ This N-blocking unit is not only inexpensive but, in addition, it can also be used to protect pyrroles which are not inductively ~tabilized.~Nevertheless, there are several disadvantages associated with the use thereof. First, the chloro group is inherently susceptible to strong bases, powerful nucleophiles, and catalytic reduction. Second, its removal must be effected in three steps, albeit simple ones which are carried out in one pot. Lipshutz and Pegrams have shown that the [2-(trimethylsilyl)ethoxy]methyl (SEM) group has considerable utility for the protection of primary, secondary, and tertiary alcohols. This publication demonstrates that the SEM moiety can also be used both for the N-protection of pyrroles, whether or not they carry stabilizing substituents, and for indole. Furthermore, lithiation of SEMsubstituted pyrrole may have promise as a source of 2alkyl pyrrole^.^ The [2-(trimethylsilyl)ethoxy]methyl unit was affixed, under mild conditions and with good efficiency, to the nitrogen atom of various pyrroles and indole (Table I), by reaction of SEM chloride* 2 with the sodium salts of the heterocycles in dimethylformamide (DMF) solution (Scheme I). Two processes were developed for the removal of the SEM moiety, the nature of which was dependent on the substituent present in the heterocyclic system. For the 2-acylpyrroles 3b-d, the addition of 4-5 equiv of boron trifluoride etherate to a dichloromethane solution of the protected compounds, at 0 O C , 9 resulted in the rapid generation of the labile N-hydroxy compounds 4b-d. These intermediates5 were not purified, but the presence thereof could be demonstrated by a low-field two-proton singlet (e.g., 6 5.50 for 4b) in the NMR spectra
203
COCH, COPh CH,Ph
methcompd oda lb lb IC Id le
91 91 75 96
Ib Ia Ia Ib I1 I1
5
7% yield 45-60 86 86 91 67 98
Methods: Ia, boron trifluoride etherate/Triton Bacetonitrile; Ib, boron trifluoride etherate/aqueous sodium acetate; 11, tetrabutylammonium fluorideiethylene diamine. a
Scheme I
1
R
[
Q
+
(CH3),S~CH,C~,0CH,CI
2
I I
H
/Le 1 R
m
.\H
R
JJ
Ct120H
3
CH,OCH,CH,SIICH,),
4
and a strong OH stretching band (3450 cm-’ for 4b) in the IR spectra of the crude products. The deprotection was completed by heating the crude products with Triton B (in acetonitrile solution, variation Ia) or with aqueous sodium acetate (variation Ib). Whereas the removal of the SEM group from the 2-benzoyl compound 3d was accomplished in high yield by method Ib, the cleavage of 3b and 3c was more efficiently effected with Triton B as the base. The cleavage of the 2-acylated SEM-protected pyrroles 3b-d could also be effected, in a single oberation, with tetra-n-butylammonium fluoride,1° but this process was inferior in terms of product yield and purity. Neither the 2-benzylpyrrole derivative 3g (see below) nor SEM-protected indole 6 could be cleaved under any of the above conditions because both of these compounds were quickly converted into highly colored insoluble materials. The scission of the protecting group could, however, be carried out with tetra-n-butylammonium fluoride (DMF/45 “C), provided that a primary amine was present in excess to trap the liberated formaldehyde. Optimization of this process (method 11) by using 6 established that ethylenediamine gave a much higher yield (98%) of indole 5 than either tert-butyl- or n-heptylamine (65% and 74% yields, respectively). The application of this technique to 3g gave 2-benzylpyrrole (le) in satisfactory yield. It would thus appear that the SEM group is particularly effective for the N-protection of pyrroles and indole. Its utility in this regard is further enhanced because it is unaffected by the following reagents (room temperature, 1 h): sodium borohydride, lithium aluminum hydride, acetic acid or trifluoroacetic acid in aqueous tetrahydrofuran, potassium fluoride in dimethyl sulfoxide, chromium trioxide-pyridine in dichloromethane, methanolic potassium carbonate and lithium tetrafluoroborate in aceto(10)Corey, E. J.; Snider, B. B. J. Am. Chem. SOC.1972,94, 2549. Corey, E. J.; Venkateswarlu, A. Zbid 1972,94, 6190.
0 1984 American Chemical Society
204
J. Org. Chem., Vol. 49, No. 1, 1984
Notes
nitrile." Both hydrogen fluoride in aqueous acetonitrile12 and boron trifluoride etherate in dichloromethane cause destruction of 6 within minutes. It was expected that combining the utility of the SEMmoiety as a protecting group with the known predominant lithiation of N-alkylpyrroles in the a-positiod3 might provide ready access to 2-alkyl-N-unsubstituted pyrroles.13J4 Furthermore, lithiation of 3a at C-2 might be expected to be even more favored than usual because of the stabilization of this species as the bicyclic chelate 7. Surprisingly, with n-butyllithium in THF-hexane at -78 to +25 "C, which are conditions known to be particularly favorable for the lithiation of N-methylpyrrole, compound 3a was inert. Similar results were obtained in the presence of tetramethylethylenediamine or when see-butyllithium was used. tert-Butyllithium at -10 "C to room temperature did, however, effect metalation within 0.5 h. Mass spectral analysis of the deuterated mixture, obtained on quenching the reaction with heavy water, indicated that a substantial percentage of the product was dideuterated (11% Do,65% D1, 23% DJ. This result did not augur well for the synthesis of pure mono-a-alkylpyrroles by this route. Indeed, the addition of 1equiv of methyl or n-butyl iodide to the lithiation solution gave 3:l and 2:l mixtures of mono- (3e-g) and 2,5-dialkylated (8a-c) products, respectively (eq l),as determined by gas-liquid partition
u
-
?
I i L S , M e 3
7
SiMe,
3a
QR
+
"",
SiMe3
3e-g
(1)
J--R J
I/RR
%Me3
8a-c
chromatography. In contrast, alkylation with benzyl bromide produced mainly the 2-benzyl compound 3g which could be isolated in 75% yield. The deblocking of this compound to 2-benzylpyrrole (le) was described above, and thus it would appear that this synthetic sequence may indeed have some promise as a source of 2-alkylpyrroles. In this regard, it was recently reported' that 3a could, in fact, be metalated with n-butyllithium at 0 "C when dimethoxyethane was used as the solvent. The lithium compound 7, on acylation with a bicyclic five-membered lactone, gave the 2-acylpyrrole derivative 9 in 62 % yield,
9
which was used in the synthesis of the ionophore antibiotic X-14547. No information was given concerning the oc(11) Lipshutz, B. H.; Pegram, J. J.; Morey, M. C. Tetrahedron Lett. 1981,22,4603. (12) Newton, R. F.; Reynolds, D. P.;Finch, M. A. W.; Kelly, D. R.; Roberts, S. M. Tetrahedron Lett. 1979, 3981. Cave, R. J.; Newton, R. F.; Reynolds, D. P. J. Chem. Soc., Perkin Trans. 1 1981, 646. (13) Brittain, J. M.; Jones, R. A.; Sepulveda Arques, J.; Aznar Saliente, T. Synth. Commun. 1982, 12, 231 and references therein. (14) Chen, J. C. Org. Prep. Proceed. Znt. 1976,8, 91.
currence of dilithiated species in this remarkably facile metalation reaction.15 The results described herein have a number of obvious synthetic implications which will be investigated in due course.
Experimental Section The melting points were determined on a Mel-Temp apparatus and are not corrected. The IR spectra were measured on a Sargent-Welch Model 3-200 IR spectrophotometer. The UV spectra were recorded with a Hewlett-Packard Model 8450 A UV/VIS spectrophotometer. The NMR spectra were obtained with a Varian EM-390 spectrometer or a Bruker WM-300 spectrometer, and the chemical shifta are recorded as parts per million (6) from internal tetramethylsilane. The low resolution mass spectra were measured on a Varian MAT CH-7 spectrometer. The high-resolution mas spectra were obtained with a Varian MAT 311A mass spectrometer. The centrifugally accelerated TLC separations were effected on a Model 7924 Chromatotron (Harrison Research, Palo Alto, CA). N-Protection of Pyrroles and Indole. Synthesis of 1[[2- (Trimethylsily1)ethoxy ]met hyllpyrrole (3a). The procedure described for 3a was used for the synthesis of all of the N-protected compounds. To a stirred suspension of sodium hydride (50% in mineral oil, 0.76 g, 15.6 mmol) in anhydrous DMF (35 mL) was added pyrrole (1mL, 14.4 mmol). When hydrogen evolution had ceased, [2-(trimethylsilyl)ethoxy]methylchloride (2;2.6 mL, 14.4 "01) was added dropwise at 0 "C. The reaction mixture was then left to come to room temperature and stirred for 1 h. The mixture was poured into ice cold 10% sodium bicarbonate solution, and the product was extracted into ether. The extract was dried over anhydrous magnesium sulfate and the solvent was removed in vacuo. The residual oil was evaporatively distilled (Kugelrohr) at 120 "C (11mm) to give 3a: 2.42 g (85%); UV (MeOH) 214 nm (c 6340); Nh4R (CDCl,) 6 0.03 (s,9 H, Me,%), 0.89 (t, 2 H, J = 8 Hz, CH2Si),3.45 (t,2 H, J = 8 Hz, OCHJ, 5.20 (s, 2 H, NCHzO),6.20 (t, 2 H, H-3,4), 6.79 (t,2 H, H-2,5). Anal. Calcd for C1,,H1dOSi: C, 60.87; H, 9.70; N, 7.10. Found C, 60.85; H, 9.71; N, 7.05. 1-[ [2-(Trimethylsilyl)ethoxy]methyl]pyrrole-2-carboxaldehyde (3b). This compound was obtained as an oil (98% yield) after purification by column chromatography on silica gel [hexane-ethyl acetate (80:20)]: UV (MeOH) 203 nm, 286 (t 15200, 14800): IR (neat) 1670 cm-'; NMR (CDC13)6 0.03 (s, 9 H, Me3Si), 0.90 (t, 2 H, J = 8 Hz, CHzSi),3.60 (t,2 H, J = 8 Hz, OCHJ, 5.80 (s,2 H, NCHZO), 6.40 (dd, 1 H, J 3 , 4 3.9 Hz, 5 4 3 = 2.8 Hz, H-4), 7.10 (dd, 1H, J4,5 = 2.8 Hz, J3,5 = 1.5 Hz, H-5), 7.20 (m, 1 H, H-3), 9.75 (s, 1 H, CHO). Anal. Calcd for Cl1Hl9NO2Si: C, 58.62; H, 8.50; N, 6.22. Found: C, 58.91; H, 8.52; N, 6.21. 1-[[2-(Trimethylsilyl)ethoxy]methyl]-2-acetylpyrrole (3c). This compound was also obtained as an oil (91%) after purification by column chromatography as described above: UV(Me0H) 284 nm (e 13700); IR (neat) 1660 cm-'; NMR (CDCl,) 6 0.03 (s,9 H, Me3Si),0.90 (t,2 H, J = 8 Hz, CH,Si), 2.50 (s, 3 H, COCH3),5.80 (9, 2 H, NCHZO), 6.30 (dd, 1 H, J3,4 = 3.5 Hz, J 4 , 5 = 2.6 Hz, H-4), 7.30 (m, 2 H, H-3,5). Anal. Calcd for Cl2Hz1NO2Si:C, 60.21; H, 8.84; N, 5.85. Found: C, 60.44; H, 8.89; N, 5.69. 1-[ [2-(Trimethylsilyl)ethoxy]methyl]-2-benzoylpyrrole (3d). This compound was also obtained as an oil (94%) after purification by column chromatography on silica gel with hexane-ethyl acetate (955) as the eluting solvent: UV (MeOH) 203 nm, 248,302 (t 18200,96 800,14 400); IR (neat) 1630 cm-'; NMR (CDCl,) 6 0.03 (s, 9 H, Me,Si), 0.90 (t,2 H, J = 8 Hz, CH2Si),3.70 (t, 2 H, J = 8 Hz, OCHZ), 5.90 ( 8 , 2 H, NCHZO), 6.30 (dd, 1 H, J 3 , 4 = 3.9 Hz, J 4 , 5 = 2.4 Hz, H-4), 6.80 (dd, 1 H, J 4 , 5 = 2.4 Hz, J 3 , 5 = 1.5 Hz, H-5), 7.30 (m, 1 H, H-3), 7.60 (m, 2 H, aryl H's), 7.85 (m, 3 H, aryl H's). Anal. Calcd for C17HZ3N02Si:C, 67.73; H, 7.69; N, 4.65. Found: C, 67.99; H, 7.80; N, 4.50. l-[[2-(Trimethylsilyl)ethoxy]methyl]indole (6). This compound too was obtained as an oil (96%) after column chromatography on silica gel with hexane-ethyl acetate (9010) as the (15) The SEM group waa removed by treatment with tetra-n-butylammonium fluoride in THF at C-20 "C. No other reactions of the lithiated species were reported.
J. Org. Chem. 1984,49, 205-207 eluting solvent: UV (MeOH) 218 nm, 266, 277, 289 (c 37500, 77 900,65 600,44 100); NMR (CDC1,) 6 0.03 (s,9 H, Me3Si),0.90 (t, 2 H, J = 8 Hz, CHzSi),3.65 (t, 2 H, J = 8 Hz, OCHz),5.65 (s, 2 H, NCHzO), 6.65 (d, 1 H, J = 3 Hz, H-3), 7.35 (m, 3 H), 7.65 (m, 2 H). Anal. Calcd for CI4Hz1NOSi:C, 67.96, H, 8.56; N, 5.66. Found C, 67.82; H, 8.39; N, 5.73. Deprotection of Pyrroles and Indole. Method Ia. Pyrrole-2-carboxaldehyde. To a stirred solution of the silyl compound 3b (1.00 g, 4.4 mmol) in dichloromethane (132 mL) cooled to 0 "C was added slowly boron trifluoride etherate (2.1 mL, 17.8 mmol). The solution was left to come to room temperature after which time stirring was continued for 1 h. Sodium bicarbonate solution (lo%, 20 mL) was added, and the organic phase was separated and evaporated in vacuo. Acetonitrile (132 mL) and Triton B (40% in methanol, 20 drops) were added, and the solution was stirred at reflux temperature for 6.5 h. The solution was poured into water and extracted with ether. The extract was washed with water, dried over magnesium sulfate, and evaporated in vacuo. The crude product was subjected to column chromatography on silica gel with hexane-ethyl acetate (80:20) as the eluting solvent to give pyrrole-2-carboxaldehyde:0.360 g (86%); mp 43 "C. 2-Acetylpyrrole. The procedure for method Ia was followed except that the reaction with boron trifluoride etherate was carried out for only 0.5 h at room temperature, and the reflux period with Triton B was shortened to 3 h. Method Ib. 2-Benzoylpyrrole. The procedure described in Ia was followed except that 5 equiv of boron trifluoride etherate was used, and the reaction mixture was stirred at room temperature for 0.25 h. The dichloromethane was not removed; instead, aqueous sodium acetate (10 equiv of a 5.5 M solution) was added, and the mixture was heated at reflux temperature for 1h. The organic phase was separated, dried, and then worked up as described above. Method 11. Indole. A mixture of 1-[[2-(trimethylsily1)ethoxy]methyl]indole (0.50 g, 2.0 mmol), tetra-n-butylammonium fluoride (1.59 g, 6.1 mmol), DMF (2.2 mL), and ethylenediamine (0.8 mL) was stirred at 45 "C for 48 h. The reaction mixture was poured into water and extracted with ether. The extract was washed successivelywith dilute hydrochloric acid and 10% sodium bicarbonate solution, and after the extract was dried, the ether was removed in vacuo. The residue was subjected to column chromatography on silica gel with hexane-ethyl acetate (41) as the eluting solvent. Indole (mp 50 "C) was thus obtained in 98% yield. 2-Benzylpyrrole ( l e ) . 1-[ [2-(Trimethylsilyl)ethoxy]methyl]-2-benzylpyrrole (3g) was deblocked in a manner identical with that described for 6. The chromatographically homogeneous oil, obtained in 67% yield, contained less than 7% 2,5-dibenzylpyrrole by mass spectral analysis while the IR and NMR spectral properties were identical with those of authentic 2benzylpyrrole.16 Lithiation and Alkylation of 1-[[2-(Trimethylsilyl)ethoxy]methyl]pyrrole. 1-[[2-(Trimethylsilyl)ethoxy]methyl]-2-methylpyrrole (3e) and 1-[[2-(Trimethylsilyl)ethoxy]methyl]-2,5-dimethylpyrrole(sa). To a solution of 3a (0.20 g, 1.015 mmol) in dry hexane (1 mL) was added 2.1 M tert-butyllithium in hexane (0.48 mL, 1.008 "01) at -10 "C. The solution was then left to stir a t room temperature for 0.5 h, and then it was cooled to -78 "C whereupon a solution of methyl iodide (0.6 mL, 9.2 "01) in anhydrous THF (1mL) was added. Stirring was continued at -78 "C for 1 h, at 0 "C for 2 h, and at room temperature for 18 h. The solution was diluted with water and extracted with ether, and the extract was washed with saturated salt solution and dried. The solvent was removed in vacuo, and the residual oil (0.175 g) was shown by gas-liquid partition chromatography (3% SE-30, 100 "C) to consist of a 3:l mixture of the 2-alkylated and 2,5-dialkylated pyrroles 3e and 8a: UV (MeOH) 214 nm (e 6070); NMR (CDCl,) 6 0.03 ( 8 , 9 H, Me3%), 0.90 (t, 2 H, J = 8 Hz, CH,Si), 2.20 (s, 3 H, CH,), 3.60 (t, 2 H, J = 8 Hz, OCH,), 5.30 (s, 2 H, N-CH,O), 5.90 (m, 1H, H-3), 6.15 (t, 1 H, H-4), 6.70 (dd, 1H, J 4 , 5 = 3.0 Hz, J3,5 = 1.8 Hz, H-5); MS, calcd for ClZH2,NOSi(molecular ion) m/e 211.1392, found m/e (16) Hobbs, C. F.; McMillin, C. K.; Papadopodas, E. P.; Van der Werf, C. A. J. Am. Chem. SOC.1962,84, 43.
0022-3263/84/1949-0205$01.50/0
205
211.1394. The presence of the dimethyl compound 8a in this mixture was supported by NMR resonances at 6 5.12 (s, N-CHzO) and 5.79 ( 8 , H-3,4) and a mass spectral molecular ion at mle 225. 1-[ [2-(Trimethylsilyl)ethoxy]methyl]-2-n-butylpyrrole -bu(3f) an4 1-[ [2-(Trimethylsilyl)ethoxy]methyl]-2,5-di-n tylpyrrole (8b). This mixture was obtained in exactly the same manner as described above. The components were separated by centrifugally accelerated TLC on silica gel using hexane-ethyl acetate (955) as the developing solvent. The mono-n-butyl compound 3f was obtained as an oil: 43% yield; UV (MeOH) 218 nm ( E 6840); NMR (CDC13) 6 0.03 (s, 9 H, Me3Si),0.89 (t, 2 H, J = 8 Hz, CHzSi),0.95 (t, 3 H, J = 7 Hz, CH3), 1.40 (m, 2 H, y-CH,), 1.65 (m, 2 H, j3-CH2),2.60 (t,2 H, J = 7 Hz, a-CHz),3.45 (t, 2 H, J = 8 Hz, OCHZ), 5.18 ( 8 , 2 H, NCHZO), 5.93 (M, 1 H, H-4), 6.09 (m, 1 H, H-3), 6.65 (m, 1 H, H-5). Anal. Calcd for C14H27NOSi:C, 66.34; H, 10.74; N, 5.53. Found: C, 66.48; H, 10.74; N, 5.50. The 2,5-di-n-butyl compound 8b was also obtained as an oil (22% yield); UV (MeOH) 225 nm (t 6700);NMR (CDCl,) 6 0.03 (s, 9 H, Me&), 0.92 (t, 2 H, J = 8 Hz, CHzSi),0.95 (t, 6 H, J = 7 Hz, CH3), 1.45 (m, 4 H, y-CH,), 1.65 (m, 4 H, D-CH,), 2.60 (t, 2 H, J = 7 Hz, (Y-CHZ),3.50 (t, 2 H, J = 8 Hz, OCHZ), 5.13 (9, 2 H, NCHzO),5.85 (s, 2 H, H-3,4). Anal. Calcd for C18H3,NOSi; C, 69.85; H, 11.39; N, 4.53. Found: C, 70.16; H, 11.18; N, 4.28. 1-[ [2-(Trimethylsilyl)ethoxy]methyl]-2-benzylpyrrole(3g). This compound was obtained as described above in 75% yield after purification by centrifugally accelerated TLC on silica gel. For analysis, a small quantity was distilled bp 60-65 "C (0.015 mm); UV (MeOH) 205 nm, 269 ( t 13 700; 426); NMR (CDC1,) 6 0.03 (s, 9 H, Me3&),0.85 (t, 2 H, J = 8 Hz, CHzSi),3.40 (t, 2 H, J = 8 Hz, CHZO), 4.05 (9, 2 H, CHZ), 5.10 (9, 2 H, NCHZO), 5.95 (m, 1 H, H-4), 6.12 (m, 1 H, H-3), 6.73 (m, 1 H, H-5), 7.30 (m, 5 H, C6H5). Anal. Calcd for C17Hz5NOSi:C, 71.08; H, 8.71; N, 4.88. Found: C, 71.27; H, 8.90; N, 4.70. Registry No. la, 109-97-7;lb, 1003-29-8; IC, 1072-83-9; Id, 7697-46-3; le, 33234-48-9; 2, 76513-69-4; 3a, 87954-20-9; 3b, 87954-21-0; 3c, 87954-22-1; 3d, 87954-23-2; 3e, 87954-24-3; 3f, 87954-25-4; 3g, 87954-26-5; 5, 120-72-9; 6, 87954-27-6; 8a, 87954-28-7; Sb, 87954-29-8.
Difluorodiiodometkane: Its Preparation, Properties, and Free-Radical Reactions Seth Elsheimer, William R. Dolbier, Jr.,* and Mark Murla Department of Chemistry, University of Florida, Gainesville, Florida 32611 Konrad Seppelt and Gerhard Paprott Freie Universitat Berlin Institut fur Anorganische und Analytische Chemie, 1000 Berlin 33, West Germany Received August 15, 1983
Contrary to what its simple formula would suggest, CFzIz has previously been available in only small amounts via difficult or low-yield procedures involving the addition of difluorocarbene to molecular iodine.' Clearly any routine use of CFzIzrequires a more practical source. We report the preparation of this potentially useful reagent in reasonable yields by fluorination of the readily available tetraiodomethane2with mercury(I1) fluoride3(eq 1). The C14 + HgF, CFz12+ HgI, (1)
-
(1) (a) Mahler, W. Znorg. Chem. 1963, 2, 230. (b) Mitach, R. A. J. Heterocycl. Chem. 1964,1,233. (c) Kesling, H. S.; Burton, D. J. Tetrahedron Lett. 1976,3358. (d) Wheaton, G. A.; Burton, D. J. J.Org. Chem. 1978,43, 2643. (2) (a) McArthur, R. E.; Simons, J. H. 'Inorganic Synthesis";Audrieth, L. F.; Ed., McGraw-Hill: New York, 1950; Vol. 3, p 37. (b! Soroos, H.; Hinkamp, J. B. J . Am. Chem. SOC.1945, 67, 1642. (3) An attempt to carry out this transformation by using a 9 1 molar ratio of KF/HgF gave unsatisfactory results.
0 1984 American Chemical Society
