Diastereoselective Episulfidation of Strained Cyclic Alkenes by a Thiophene Endoperoxide versus Epoxidation by Dimethyldioxirane

Abstract

Thiophene endoperoxide 2, which was prepared by photooxygenation of thiophene 1, transfers a sulfur atom (up to 92%) to strained cycloalkenes to form thiiranes when thermolyzed in their presence. The diastereomeric pair cis/trans-cyclooctene (5b) reacted stereoselectively, which speaks for a concerted process rather than open dipolar and/or diradical intermediates. The set of chiral cyclooctenols 5c-e was also investigated, and the relative configurations of the respective thiiranes were assigned by chemical correlation and NMR spectral and X-ray analysis. The first-order kinetics of the process clearly shows that the endoperoxide 2 itself is not the sulfur-transferring species, but it is thermally transformed to the intermediates I and II. Whereas intermediate II is responsible for the competitive formation of elemental sulfur, intermediate I, presumably an oxathiirane, is the active sulfur-transferring species. The episulfidation was compared with the epoxidation by the related dimethyldioxirane, and both show the same qualitative trends in the diastereoselectivity and the reactivity toward the alkenes 5a-e.

Generation, Reactivity and Uses of Sulfines in Organic Synthesis

“…Recently, sulfines have been studied theoretically using density functional theory. 2016, 1630-1650 www Further reports by Waldemar et al describe a sulfine acting as a dipole for a carbon-carbon double bond, [112] or a carboncarbon triple bond. [108] This reactivity of the sulfines acting as dipoles has also been established practically.…”

Episulfidation of Strained Cycloalkenes in the Thermolysis of 5-Aryloxy-1,2,3,4-thiatriazoles

“…trans ‐9‐Thiabicyclo[6.1.0]nonane ( trans ‐3b): 5b Yield 641 mg (80%); m.p. 57−58 °C (ref 5b. 57−58 °C).…”

Photochemical and Electrochemical Oxygenation of Thiophenes, Benzo[b]Thiophenes and Dibenzothiophenes; Photochemical and Electrochemical Behaviour of Their Oxygenated Intermediates and Products

“…20,21 In the presence of triphenylphosphine, the sulfur moiety is extruded giving triphenylphosphine sulfide, whilst the enetrione 15 cyclises to furan system 16 (Scheme 3). 20,21 In the presence of triphenylphosphine, the sulfur moiety is extruded giving triphenylphosphine sulfide, whilst the enetrione 15 cyclises to furan system 16 (Scheme 3).…”

“…In the case of cyclohexeno annelated thiophenes 13, the endoperoxides 14 formed upon reaction with singlet oxygen can also transfer the sulfur moiety to cycloalkenes transforming these to thiiranes, while themselves forming ene-triones 15. 20,21 In the presence of triphenylphosphine, the sulfur moiety is extruded giving triphenylphosphine sulfide, whilst the enetrione 15 cyclises to furan system 16 (Scheme 3). 22 An endoperoxide intermediate is also postulated in the methylene blue-sensitized photooxygenation of 2,3-dimethyl-4,5,6,7-tetr ahydrobenzo[b]thiophene 17 in methanol, which gives cyclic sulfoxide 18 (Scheme 3).…”