J. Org. Chem. 1984,49,191-193 suspension was filtered under vacuum to remove triethylamine hydrobromide and selenium, and the filtrate was washed with water, quickly filtered through a layer (-4.0 g) of potassium carbonate, and dried over sodium sulfate. The dichloromethane was removed under reduced pressure on a rotary evaporatorbelow room temperature, and the residue was carefully pyrolyzed (50-75 "C) with a heat gun in a bulb-to-bulb distillation apparatus under reduced pressure, continually collecting the volatile selone in a dry ice/acetone-cooled receiver. Generally, the selone is pure by GLC and no further purification is necessary. 2,2,4,4-Tetramethylpentane-3-selone (7). Deep blue seione 7 was obtained from hydrazone'l in 65% yield by distillation at 0.1-5 torr. All physical constants and spectra were identical with those reported in the l i t e r a t ~ r e . ~ (-)-Selenofenchone(8). The deep blue selone 8, identical in all respecta with that previously reported: was obtained from the hydrazone'l in 76% yield, by distillation at 0.5-5 torr. 2,2,5,5-Tetramethyl-3-oxocyclopentaneselone 3-Ethylene Ketal (9). Deep blue selone 9 was prepared from the hydrazonels by a modification of the general procedure. Three equivalents of triethylamine were used, and the filtrate was washed with water instead of dilute hydrochloric acid. The selone was obtained in 80% yield by distillation at 0.5-5 torr; bp 70 "C (0.1 torr) (Kugelrohr oven temperature); 'H NMR (CC14)6 3.90 (s,4 H), 2.17 (9, 2 H), 1.32 ( 8 , 6 H), 1.16 (9, 6 H); 13C NMR (CDC13) 6 292.75 (C=Se), 117.48, 65.04, 60.16, 46.22, 31.67, 23.86; MS, m J e 262 (%3e) (M'); IR (neat) 1470,1450,1380,1360,1300,1220,1160, 1140,1070,1050,1020,980,950, 785, 760 cm-'. Anal. Calcd for CllH,s02Se: C, 50.58; H, 6.93. Found: C, 50.87; H, 6.82. Preparation of selone 9 via the phosphazine, mp 140-140.5 "C dec, according to the standard procedurela afforded this compound in 48% overall yield. 2,2,5,5-Tetramethyl-3-cyclopenteneselone (10). Deep blue selone 10 was prepared by a modification the general procedure using 6.3 mmol of hydrazone.l8 Since this selone is quite volatile, the solvent was removed by a stream of nitrogen at atmospheric pressure. Selone 10,identical with that previously reported,la was obtained in 70% yield by distillation at 16-20 torr. This reaction was also run on a 33-mmol scale, affording 10 in 60% yield. 2,2,5,5-Tetramethylcyclopentaneselone (1 1). Deep blue selone 11 was prepared from the hydrazone,19 according to the general procedure. The selone was isolated in 68% yield by distillation at 16-20 torr: mp 74-77 "C; 'H NMR (CDC13)6 1.21 (12 H, s), 1.93 (4 H, 8 ) ; 13CNMR (CDC13)6 297.8 (C=Se), 64.2, 37.4,29.3; MS, m / e 204 (M+) (%e); IR (film) 1461,1381,1361, 1220, 1056 cm-'. Anal. Calcd for C9H16Se: C, 53.20; H, 7.94. Found: C, 53.02; H, 7.86. 2,2,6,6-Tetramethylcyclohexaneselone(12). Deep blue selone 12 was prepared from the hydrazone, mp 46-47 OC, by the general procedure. The selone was obtained in 73% yield, by distillation at 0.1-5 torr: bp 28 "C (0.05 torr) (Kugelrohr oven temperature); 2WMHz 'H NMR (CDClJ 6 1.39 (12 H, s), 1.78-1.79 (6 H, br s); 13CNMR (CDClJ 6 294.7 ( M e ) , 58.9,38.4, 33.5, 18.3; MS, m / e 262 (M+) (%e); IR (neat) 1465,1450, 1380, 1360,1220,1065, 990,975,760 cm-'. Anal. Calcd for CloH16Se: C, 55.30; H, 8.35. Found C, 55.42; H, 8.46. Preparation of selone 12 via the phosphazine, mp 115-123 "C, according to the standard procedurela afforded this compound in 40% overall yield. 1,1,3,3-Tetramethylindan-2-selone (13). Deep blue selone 13 was prepared from the hydrazone, according to the general procedure. Selone 13,identical with that previously reported,1bp20 was obtained in 80% yield by distillation at 0.5-5 torr; IR (neat) 1590, 1485, 1455, 1375, 1358, 1310, 1050, 1020, 755 cm-'.
Acknowledgment. We thank the New Mexico State University Arts and Sciences Research Center for partial financial support of this research (Grant 1-3-43673) and (17)Barton, D.H. R.; Guziec, F. S., Jr.; Shahak, I. J. Chem. SOC. Perkm Trans. 1 1974, 1794. (18)Cullen, E. R.; Guziec, F. S., Jr., manuscript in preparation. (19)de Mayo, P.; Petrasiunas, G. L. R.; Weedon, A. C. Tetrahedron Lett. 1978, 4621. (20) Klages, C.-P.; Voss, J. Chem. Ber. 1980, 113,2255.
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Dr. E. R. Cullen for providing starting materials for the preparations of selone 9. Registry No. 7, 56956-23-1; 7 hydrazone, 33420-22-3; 8, 56956-24-2;8 hydrazone, 87900-48-9;9,87842-33-9;9 hydrazone, 87842-34-0; 9 phosphoranylidenehydrazone, 87842-35-1; 10, 79958-61-5; 10 hydrazone, 81396-37-4; 11, 87842-36-2; 11 hydrazone, 70302-22-6; 11 phosphoramylidenehydrazone, 70302-23-7; 12, 87842-37-3; 12 hydrazone, 87842-38-4; 12 phosphoranylidenehydrazone, 87842-39-5; 13, 74768-64-2; 13 hydrazone, 74768-84-6; Se02, 7446-08-4; Se2Br2,7789-52-8.
Aerosol Direct Fluorination. Indirect Syntheses of Perfluorocyclic Ketones James L. Adcock* and Mark L. Robin
Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37996-1600 Received June 21, 1983
The aerosol direct fluorination method provides a continuous process for the production of perfluorocarbons from hydrocarbons with efficient fluorine utilization and minimal fragmentation.' The application of this process to alkanes, ethers, cycloalkanes, ketals, and ketones has been dem~nstrated.'-~Whereas the aerosol direct fluorination of alicyclic ketones yields the corresponding perfluoro ketone as the majority product,2 aerosol fluorination of cyclic ketones has produced none of the perfluorinated analogues. In the case of cyclopentanone, the major product was F-pentanoyl fluoride, resulting from the opening of the cyclopentyl ring? aerosol direct fluorination of cyclohexanone produced only nonvolatile products; no evidence for the formation of F-cyclohexanone was However, on employment of a two-step process, perfluorocyclopentanone and perfluorocyclohexanone have been synthesized. Sulfuric acid hydrolysis of the appropriate perfluorinated ketal or ether, formed via aerosol fluorination of the corresponding ketal or ether, produced the corresponding perfluoro cyclic ketone in high yields. Previous preparations of F-cyclopentanone and Fcyclohexanone are relatively few in number; the only synthesis involving direct fluorination is that reported by Holub and Bigelow wherein F-cyclopentanone was formed in trace amounts from the direct fluorination of cyclopentanone.s F-Cyclopentanoneand F-cyclohexanonehave been prepared via the treatment of the corresponding 2,2-dichloroperfluoro cyclic ketones or 1,2-dichloroperfluorocycloalkene epoxides with potassium fluoride in tetramethylene sulfone6and by the contact of Lewis acids or bases with the appropriate perfluor olefin epoxides? In addition to the above methods, Tatlow et a1.* prepared (1)(a) Adcock, J. L.; Horita, K.; Renk, E. B. J.Am. Chem. SOC.1981, 103,6937. (b) Adcock, J. L.; Renk, E. B. US.Patent 4330475,May 1982. (2)Adcock, J. L.;Robin, M. L. J. Org. Chem. 1983, 48, 3128. (3)Adcock, J. L.;Robin, M. L. J. Org. Chem. 1983,48, 2437. (4)Robin, M.L.;unpublished results. (5)Holub, F. F.;Bigelow, L. A. J. Am. Chem. SOC.1960, 72, 4879. (6)(a) Anello, L. G.; Price, A. K.; Sweeney, R. F. J. Org. Chem. 1968, 33,2692. (b) Price, A. K.; Sweeney, R. F. (Allied). US.Patent 3350457, 1967. (c) Anello, L. G.; Sweeney, R. F. (Allied). Ibid. 3 379 765, 1968. (7)(a) Coe, P. L.; Sleigh, J. H.; Tatlow, J. C. J. Fluorine Chem. 1980, 15,339. (b) Moore, E. P.; Milan, S., Jr. (E. I. duPont de Nemours & Co.). Brit. Pat. 1019 788. 1966. IC) E.I. duPont de Nemours & Co. Fr. Pat. 1416013,1965.(d)'Moore, E.'P.; Milan, A. C. ( E L duPont de Nemours & Co.). US. Patent 3 321 515,1970. (8)Clayton, A. B.; Stephens, R.; Tatlow, J. C. J. Chem. SOC.1965, 7373.
0 1984 American Chemical Society
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J. Org. Chem., Vol. 49, No. 1, 1984
Notes
Scheme I
Ia, n = 1 b,n=2
IIa, n b,n
Scheme I1
IVa, n = 1 b,n=2
= 1 = 2
/
Va, n = 1 b,n=2
CFz-C=O I
\ C F~ CF~
IIIa, n = 1 b.n=2
IIIa, n = 1 b,n=2
F-cyclopentanone by the cleavage of methyl nonafluorocyclopentyl ether with sulfuric acid and F-cyclohexanone by the cleavage of methyl or fluoromethyl undecafluorocyclohexyl ether with sulfuric acid. Discussion The syntheses of F-cyclopentanoneand F-cyclohexanone were effected via two separate two-step reaction sequences. Scheme I outlines the syntheses of the perfluoro cyclic ketones in a two-step process from the corresponding methyl ethers. F-Methoxycyclopentane (IIa) and Fmethoxycyclohexane (IIb) obtained from the aerosol direct fluorination of the corresponding hydrocarbon ethers (Ia,b) in 22% and 32% yields, respectively, were converted to F-cyclopentanone (IIIa) and F-cyclohexanone (IIIb) by hydrolysis with 100% sulfuric acid at 340-360 OC in 89% and 82% yields, respectively. F-Methoxycyclopentaneand F-methoxycyclohexane comprised 57% and 90%, respectively, of the total products collected by weight from the aerosol reactor. Physical losses due to unfluorinated starting materials "freezing out" in the first reaction zone reduced overall yields to the value cited.g F-Methoxycyclopentane and F-methoxycyclohexane have been previously prepared by the photochemical reaction of trifluoromethyl hydrofluorite and the corresponding perfluorocycloalkene.lOJ1 The perfluoro ethers IIa and IIb are stable compounds: after 16 h at 200 "C in the presence of 100% sulfuric acid, F-methoxycyclopentane showed no signs of reaction. At 340-360 OC in the presence of 100% sulfuric acid both perfluoro ethers from their respective perfluoro ketones (IIIa,b) in high yields. In each case only the perfluoro ketone and unreacted perfluoro ether were found in the reaction mixture. Any other products were present only in trace amounts. Both perfluoro ketones are extremely hygroscopic and react readily with water to form the much less volatile monohydrates.Ba This suggests that in the aerosol direct fluorinations of cyclopentanone2 and cyclohexanone4any perfluoro ketone formed might have become hydrated due to reaction with residual water inside the reactor, explaining the fact that no perfluoro ketones could be isolated from those reactions. Scheme I1 outlines the syntheses of F-cyclopentanone and F-cyclohexanone in a two-step process from the appropriate ketals. Aerosol direct fluorinations of 1,4-diox(9) The aerosol system is dependent on the generation of a particulate aerosol which is ideally crystalline, of uniform size, and with little tendency to aggregate. If the conditions for producing the aerosol are ideal, percent yields based on throughputs and product percent distributions will differe by only a few percent; aa molecules deviate from this ideality, the percent yields based on throughput fall, due to physical losses within the aerosol generator and initial reaction stage (see ref 1). (10)Proter, R. S.; Cady, G. H. J . Am. Chem. SOC.1957, 79, 5625. (11) Toy, M. S.; Stringham, R. S. J . Fluorine Chem. 1975, 5 , 481.
aspiro[4.4]nonane (IVa) and 1,4-dioxaspiro[4.5]decane (IVb) produce the previously unknown F-1,4-dioxaspiro[4.4]nonane (Va) and F-l,Cdioxaspiro[4.51decane (Vb) (74% and 76%, respectively, of the total product collected by weight) in percent yields based on throughout of 14% and 12%, respectively. As previously mentioned, low yields are mostly due to physical losses in the r e a ~ t o r . ~ Both perfluoro ketals are extremely stble compounds: F-1,4-dioxaspiro[4.5]decane showed no signs of reaction after 26 h at 350 "C in the presence of 100% sulfuric acid, F-1,4-Dioxaspiro[4.4]nonane(Va) and F-l,4-dioxaspiro[4.5]decane (Vb) were, however, converted to F-cyclopentanone and F-cyclohexanone via hydrolysis with 100% sulfuric acid at 500 O C in 45% and in 100% yields, respectively. In the case of F-cyclopentanone, the lower yield is believed to be due to more extensive hydration of the perfluoro ketone at the higher temperature. F-Cyclopentanone is more affected because more ring strain would be relieved upon hydrate formation than in the case of F-cyclohexanone, and hence one would predict F-cyclopentanone to be more hygroscopic than F-cyclohexanone. Experimental Section The basic aerosol fluorinator design and a basic description of the process are presented elsewhere;' a modified aerosol generator was adapted to a flash evaporator fed by a syringe pump (Sage Model 341a) driving a 5.000-mL Precision Sampling Corp. "Preeaure-lok" syringe? The workup of products following removal of hydrogen fluoride consisted of vacuum line fractionation, infrared assay of fractions, gas chromatographic separation of components by using either a 7 m X in. 13% Fluorosilicone QF-1 (Analabs) stationary phase on 60-80-mesh, acid-washed Chromosorb B conditioned at 225 "C (12 h) or a 4 m X 3/8 10% SE-52 phenyl-methyl silicone rubber on acid washed 60-80-mesh Chromosorb P column conditioned at 250 "C (12 hours). Following gas chromatographic separation (Bendix Model 2300, subambient multicontroller) all products of significance were collected, transferred to the vacuum line, assayed, and characterized by vapor-phase infrared spectrophotometry (Perkin-Elmer 1330), electron-impact (70 eV) and chemical-ionization (CH, plasma) mass spectrometry (Hewlett-Packard GC/MS system: 5710A GC,5980A MS, 5934A computer), and '?F nuclear magnetic resonance (JEOL FXSOQ, omniprobe) in CDC13with 1% CFCl, as an internal standard. Elemental analyses were performed by Schwarzkopf Microanalytical Laboratory, Woodside, NY. The above characterizations and detailed aerosol reaction parameters are available as supplementary material. Aerosol Fluorination of Methoxycyclopentane. Methoxycyclopentane was prepared by the method of Vogel from cyclopentanol'2 A pump speed corresponding to 3.7 mmol/h was established and 2.40 mL (2.05 g, 20.5 mmol) of methoxycyclopentane was delivered over a 5.5-h period. Details of the aerosol parameters are available as supplementary material. For the photochemically finished reaction 2.42 g of crude product was isolated; separation on the QF-1 column (temperature program: 20 OC, 10 min; 5 "C/min to 100 "C; 100 " C , 1 min; 50 OC/min to 180 OC) yielded 1.39 g (57%) of pure F-methoxycyclopentane, corresponding to a yield of 22% based on total methoxycyclopentane injected. The 19F NMR spectrum of F-methoxycyclo-
J. Org. Chem. 1984,49, 193-195 pentane agreed with that appearing in the literature." Hydrolysis of F-Methoxycyclopentane. F-Methoxycyclopentane (0.321 g) was condensed onto an approximately equal volume of fuming sulfuric acid (30% SO3) which had been degassed and vacuum stripped to remove the SO,; the reaction tube was then sealed under vacuum and heated in a tube furnace at 360 "C for 24 h. The tube was then opened on the vacuum line and the reaction mixture fractionated through -131 and -196 "C cold traps, most of the material being collected in the -131 "C trap. Products from the -131 "C fraction were separated on the SE-52 column (temperature program: -10 "C, 5 min, 0.5 "C/min to 20 "C) and identified as F-cyclopentanone" (0.140 g) and unreacted F-methoxycyclopentane (0.103 9). The percent yield of F-cyclopentanonebased on F-methoxycylopentanereacted was thus 89%, and the percent conversion for the reaction was 61%. Aerosol Fluorination of Methoxycyclohexane. Methoxycyclohexane was prepared by the method of Vogel from cyclohexanol.12 A pump speed corresponding to 3.8 mmol/h was established, and 3.30 mL (2.89 g, 25.3 mmol) of methoxycyclohexane was delivered over a 6.75-h period. From the 3.32 g of crude product collected 2.99 g (90%) of pure F-methoxycyclohexane was isolated (QF-1 program: 35 "C, 10 min; 4 "C/min to 100 "C, 100 "C/min; 50 "C/min to 180 "C) which correspond to a yield of 32% based on total methoxycyclohexane injected. The lsF NMR spectrum of F-methoxycyclohexane was in agreement with the appearing in the literature." Hydrolysis of F-Methoxycyclohexane. F-Methoxycyclohexane (0.308 g) was treated with 100% sulfuric acid as described above and heated for 14 h at 340 "C. After a workup of the reaction mixture as for F-methoxycyclopentane, separation on the SE-52 column (0 "C, 10 min; 1 "C/min to 100 "C) yielded F-cyclohexanone" (0.066 g) and unreacted F-methoxycyclohexane (0.202 9). The percent yield of F-cyclohexanone based on the amount of F-methoxycyclohexane reacted was 82%, and the percent conversion to product for the reaction was 28%. Aerosol Fluorination of 1,4-Dioxaspiro[4.4]nonane. 1,4Dioxaspiro[4.4]nonane was prepared by the method of Daignault A pump speed corresponding and Eliel from cy~lopentanone.~~ to 4.2 mmol/h was established, and 3.0 mL (3.21 g, 25.1 mmol) of 1,4-dioxaspiro[4.4]nonanewas delivered over a 6-h period. Details of the aerosol fluorination parameters are available as supplementary materials. The crude product (1.65 g) was separated on the QF-1 column (30 "C, 5 min; 5 "C/min to 100 "C; 100 "C, 1min; 50 "C/min to 180 "C) and yielded 1.22 g (74%) corresponding to a 14% yield of pure F-1,4-dioxaspiro[4.4]nonane, based on total 1,4-dioxaspiro[4.4]nonaneinjected. The 'ONMR consists of three singlets of equal intensity a t cp -85.32, -130.36, and -131.69. Anal. Calcd for C7FI2O2: ._ C, 24.44, F, 66.26. Found: C, 24.22; F, 66.25. Hydrolysis of F-1,4-Dioxaspiro[4.4]nonane. F-l,6Dioxaspiro[4.4]nonane (0.156 g) was treated with 100% sulfuric acid (as prepared previously) and was heated for 24 h at 450 "C. Separation of the products on the SE-52 column (-10 "C, 5 min; 0.5 "C/min to 50 "C) yielded 0.024 g of F-cyclopentanone (isolated as the monohydrate) and 0.07 g of unreacted F-1,4-dioxaspiro[4.4]nonane. The percent yield of F-cyclopentanone based on the amount of F-l,4-dioxaspiro[4.4]nonanereacted was 45%, and the percent conversion to product for the reaction was 23%. Aerosol Fluorination of 1,4-Dioxaspir0[4.5]decane. 1,4Dioxaspiro[4.5]decane was prepared by the method of Daignault and Eliel from cycl~hexanone.'~ A pump speed corresponding to 4.3 mmol/h was established and 3.0 mL (3.1 g, 21.5 mmol) of 1,4-dioxaspiro[4.5]decanewas delivered over a 5-h period. The crude products (1.28 g) were separated on the QF-1 column (50 "C, 5 min; 2 "C/min to 100 "C; 100 "C, 1min; 50 "C/min to 180 "C) and yielded 0.97 g (76%) pure F-1,4-doxaspiro[4.5]decane, corresponding to a percent yield of 12% based on total 1,4-dioxaspiro[4.5]decane injected. The F-1,4-dioxaspiro[4.5]decane '9 NMR consisted of a singlet at I#J -83.22 and a broad multiplet a t I#J -132.02 (4:lO relative intensity). Anal. Calcd for C8F1402: C, 24.38; F, 67.49. Found: C, 23.85; F, 66.78. Hydrolysis of F-1,4-Dioxaspiro[4.5]decane. F-1,4-Dioxaspiro[4.5]decane (0.198 g) was treated with 100% sulfuric acid ~
(12) Vogel, A. I. J. Chem. SOC.1948, 1809. (13) Daignault, R. A.; Eliel, E. L. Org. Synth. 1967, 47, 37.
193
(as prepared previously) and was heated for 18 at 500 "C. Separation of the products on the SE-52 column (0 "C, 10 min; 1 "C/min to 100 "C) yielded 0.050 g F-cyclohexanone and 0.127 g unreacted F-1,4-dioxaspiro[4.5]decane, both identified from their infrared spectra. The percent yield of F-:yclohexanone based reacted was loo%, and the percent on F-1,4dioxaspiro[4.5]decane conversion to products for the reaction was 36%.
Acknowledgment. This work was supported in part by the Office of Naval Research, whose support is gratefully acknowledged. Registry No. Ia, 5614-37-9; Ib, 931-56-6; IIa, 788-40-9; IIb, 4943-06-0; IIIa, 376-66-9; IIIb, 1898-91-5;IVa, 176-32-9;IVb, 177-10-6; Va, 87901-77-7; Vb, 87901-78-8.
Supplementary Material Available: Characterization data for the produds (IR,MS, ? F NMR,aermol parameters) (6 pages). Ordering information is given on any current masthead page.
Synthesis of 3-Nitro-5-acylpyridines by Condensation of Sodium Nitromalonaldehyde/Tosyl Chloride with 2-Amino-1-acyl Olefins. Evidence for the Intermediacy of 3-Chloro-2-nitroacrolein Jacob M. Hoffman,* Brian T. Phillips, and David W. Cochran
Merck Sharp & Dohme Research Laboratories, West Point, Pennsylvania 19486 Received August 12, 1983
A search for a convenient synthesis of 3-nitro-5acetylpyridine (la) led to an investigation of the method developed by Fanta.' Ethyl 2-methyl-5-nitronicotinate (la) was prepared in 35% yield by the condensation of sodium nitromalonaldehyde (2)2 with ethyl 3-aminocrotonate, which was assumed to be generated in situ at -10 "C from ethyl acetoacetate and ammonia. However, with 4-amino-3-buten-2-one3 or ethyl 3-aminocrotonate prepared by other methods: the reaction with sodium nitromalonaldehyde gave only traces (- 1%) of the respective nitropyridines l a and Id. Closer examination revealed that the solid intermediate formed in the Fanta procedure and assumed to be ethyl 3-aminocrotonate is, in fact, the ammonium salt of ethyl acetoacetate. When this solid is warmed to room temperature, ammonia gas is rapidly evolved, leaving a liquid residue identified as ethyl acetoacetate. Furthermore, when 1 equiv of ammonium hydroxide was added to a mixture of sodium nitromalonaldehyde and ethyl acetoacetate in water, the literature yield (34%) of Id wm reproduced. These results coupled with literature precedent6 would suggest that the formation of Id involved initial condensation of the anion of ethyl acetoacetate with sodium nitromalonaldehyde, amination of the dicarbonyl intermediate with ammonia, and subsequent ring closure. This approach was not ap(1) Fanta, P. E. J. Am. Chem. SOC.1963, 75, 737. (2) Fanta, P. E."Organic Synthesis";Wiley: New York, 1963; Collect. VOl. IV, p 844. (3) Micheel, F.; Dralle, H. Liebigs Ann. Chem. 1963, 670, 57. 1922, 121, 2216; prepared most conven(4) Hope, E.J. Chem. SOC. iently by the method in ref 5. (5) Zymalkowski, F.;Rimek, H. Arch. Pharm. (Weinheim, Ger.) 1961, 294, 759. (6) For a review, see: Fanta, P. E.; Stein, R. A. Chem. Rev. 1960,60, 261. For a more recent reference, see: Kvitko, S. M.; Maksimov, Y. V.; Paperno, T. Y.; Perekalin, V. V. J. Org. Chem. USSR (Engl. Traml.) 1973, 9,477 (2%. Org. Khim. 1973, 9, 471).
0022-3263/84/1949-0193$01.50/00 1984 American Chemical Society
