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The Decomposition of Thiirane 1,l-Dioxides (Episulfones) F. G. Bordwell, Joel M. Williams, Jr.,' Earle B. Hoyt, Jr., and Bruce B. Jarvis Contribution from the Department of Chemistry, Northwestern University, Evanston, Illinois 60201. Received May 19, 1967 Abstract: The first-order rates of decomposition of the episulfones, 2-phenylthiirane 1,l-dioxide (l), trans-2,3diphenylthiirane 1 ,I-dioxide (2), and cis-2,3-diphenylthiirane 1,I-dioxide (3) (to alkene and sulfur dioxide), were
found to correlate surprisingly well with the ionizing power of the medium. The rates were found to be accelerated by alkoxide ion and were first order in alkoxide ion when the concentration was sufficiently high. Solvolytic decomposition of 2 gave trans-stilbene stereospecificallyand 3 gave cis-stilbenestereospecifically,but trans-stilbenewas obtained from 3, as well as from 2, when alkoxide ion was present. Deuterium exchange experiments showed that in the presence of methoxide ion 3 underwent exchange, with retention of configuration, at a rate considerably faster than its rate of epimerization to 2. The solvolytic decompositions of 1-3 are represented as occurring by way of diradical intermediates; a diradical anion intermediate is assumed for the alkoxide ion promoted reactions, The latter reaction is believed to involve addition of methoxide ion to the sulfone grouping.
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-20° ethods are now available for the preparation of PhCHNz SO2 both symmetrical and unsymmetrical thiirane in ether liquid 1,l -dioxides (episulfones). Staudinger and Pfenninger found that diphenyldiazomethane and sulfur diPh, ,Ph oxide gave tetraphenylthiirane 1, l-dioxide;2 this method has since been applied to prepare the parent h e t e r o c y ~ l e , and ~ ~ its 2,3-diaryl-2,3-dieth~I,~~ 2,3-dimeth~l,~and 2,3-dipheny15v6 derivatives. Re2 (55%) 3 (45%) cently Opitz and Fischer have shown that a variety of The composition of the mixture is based on the unsymmetrical thiirane dioxides can be obtained from proportions of trans- and cis-stilbenes obtained on the reaction of sulfenes and dia~ornethane.~ thermal decomposition. The cis isomer 3 was obMost thiirane 1,l-dioxides decompose near room tained in a purity of about 9 5 % by warming a methytemperature to give alkenes and sulfur dioxide. 2-7 lene chloride solution containing 2 and 3 for about 10 For cis- and trans-2,3-dimethylthiirane 1,l-dioxides min, which caused most of the 2 present to decompose, and cis-2,3-diphenylthiirane 1,l-dioxide the decomfollowed by precipitation of 3 with pentane. The 3 positions occur stereospecifically with retention of obtained in this way decomposed stereospecifically configuration of the alkene.4-6 The present study was to cis-stilbene in agreement with previous reports.j.638 initiated to determine the effect of base on the rate and First-Order Decompositions. At 0" the rate of stereochemistry of episulfone decompositions. This decomposition of 2 was faster than that of 3 by an has been accomplished and, in addition, information amount sufficient to allow spectrophotometric deterpertinent to the mechanism of these decompositions mination of the individual rates using a mixture of has been obtained. isomers. At 25 O the decomposition of 3 interfered with Phenylthiirane 1,1-dioxide (1) was prepared by the the determination of the infinity absorbance for 2, method of Opitz and F i ~ c h e r . ~ but the rate for 2 could be obtained by the GuggenPhCHzSOzCl Et,N CHzN, -C heim method. The rates varied appreciably with solvent, as is brought out in Table I. PhCH-CHZ Examination of Table I shows that the rate of de\s/ Et3NH+C1N2 composition of the three episulfones (to alkene and o4 \o sulfur dioxide) increases markedly (over 1000-fold) 1 with increasing ionizing power of the medium. A plot of log k/ko for 1 against Grunwald-Winstein Y Application of Staudinger's method2 t o phenyldivalues for the solvolysis of t-butyl chlorideg gave a azomethane using a temperature below -20" gave a surprisingly good line for the aqueous dioxane runs low yield of a mixture consisting of about 5 5 % trans[Figure 1; slope (m) E 0.51. The rate in water, oband 45 % cis-2,3-diphenylthiirane 1,l-dioxides (2 and 3, tained by extrapolation, was 1.4 sec-'. Plots of log respectively). k for 1 us. volume per cent water for aqueous dioxane, (1) National Institutes of Health Predoctoral Fellow, 1964-1966. acetonitrile, and dimethyl sulfoxide solutions gave a (2) H. Staudinger and F. Pfenninger, Eer., 49, 1941 (1916). series of curves which converged with increasing water (3) (a) G. Hess, E. Reichold, and S. Majumdar, ibid., 90,2106 (1957); content. The rate in pure water, obtained by extrap(b) L. V. Vargha and E. Kovacs, ibid., 75, 794 (1942). (4) (a) N. P. Neureiter and F. G. Bordwell, J . Am. Chem. Soc., 85, olation, was about 1 sec-'.
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1209 (1963); (b) N. P. Neureiter, ibid., 88, 558 (1966). ( 5 ) L. A. Carpino and L. V. McAdams, 111, ibid., 87, 5804 (1965). (6) N. Tokura, T. Nagai, and S. Matsurnura, J . Org. Chem., 31, 349 (1966). (7) G. Opitz and H. Fischer, Angew. Chem. Intern. Ed. Engl., 4, 70 (1965).
(8) The relative instability of 2 ( f 1 / 2 = 2.8 min in chloroform at 25" as compared to 89 min for 3) no doubt accounts for its presence going undetected previously. (9) E. Grunwald and S. Winstein, J . Am. Chem. Soc., 70, 846 (1948); A. H. Fainberg and S. Winstein, ibid., 78, 2770 (1956).
Bordwell, Williams, Hoyt, Jaruis
Decomposition of Thiirane I,I-Dioxides
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