Thiiranes alkylidene

Alkylidene sulfenes (75), generally prepared by the dehydrohalogenation of alkylsulfonyl chlorides, add readily to electron-rich multiple bonds. For example, with enamines, the thietane dioxide (e.g., 76) is formed diazoalkanes yield thiirane dioxides (episulfones) and imines (Schiff bases) afford 1,2-thiazetidine 1,1-dioxides. There are available numerous reviews of sulfenes, including cycloaddition reactions.102... 

In the middle of the 1950s, Knott reported the synthesis of dyesmffs based on benzothiazole derivatives. Alkylation of Al-methylbenzo-l,3-thiazole-2-thione with a-bromoacetophenone and deprotonation of the resulting thiocarbonylium salt 5 yielded, after spontaneous desulfurization of the intermediate thiirane (7), the alkylidene derivative 8 (18) (Scheme 5.1). In order to rationalize the reaction, thiocarbonyl ylide 6 was proposed as the precursor of thiirane 7. To the best of our... 

Geng etal. used DFT to examine abstraction of sulfur from thiirane by alkylidene carbenes <2005HX1402>. The greater the electronegativity of the carbene substituents (XYC=C), the lower the activation energy for abstraction. Electronic factors were found to be much more important than steric factors. 

Rademacher and co-workers studied the gas-phase thermolysis of 4-substituted 3,3,5,5-tetramethyl-3,5-dihydo-477 pyrazoles by photoelectron spectroscopy <1996T1695>. Among the systems investigated was 76, which afforded 77 at 470 °C. The alkylidene thiirane rearranged at 640 °C to thiol 78. Thermolysis of 79 at 425 °C gave alkylidenethi-irane 3 -oxide 80, which lost SO at 700 °C to yield allene 81 (Scheme 13). 

Synthesis and reactions of 2-alkylidene thiiranes and thietanes 07S2755. 

Some interesting chemistry of the thione has been revealed. Cyclic additions of diazoethane to 36 gave the thiiran (128) via the initial thia-zoline adduct (129) (Bachi et al., 1978). Treatment of 128 with triphen-ylphosphine resulted in the alkylidene azetidinone (130) in high yield. Oxidation of the thione (36) with ozone gave the 2,4-azetidinedione (131) (Bachi et al., 1978). 

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