Methylene thietanes reactions

Flash vacuum pyrolysis (FVP) represents a special method for inducing decomposition of thietane compounds. Block et al. succeeded for the first time in the preparation of methylene sulfine in the gas phase, applying this method to thietane 1-oxide. The reaction starting at 600°C was followed by mass and microwave spectroscopy. 

Hydroxy-3,4-dihydro-2H-pyrido[2,l-b][l,3]thiazin-5-ium chloride was formed when 2-hydroxy-3-(2-pyridylthio)propyl chloride was stirred in methylene chloride overnight (92JOC6335). When the reaction was carried out in methanolic sodium methylate, 3-(2-oxo-l,2-dihydro-l-pyridyl) thietane was obtained in 58% yield. 

Intramolecular alkylation of the sulfur atom of thietanes also is invoked in reactions of a-haloalkylthietanes, for example, the formation of 75 in reactions of alcohol 74. The salt 75 has been isolated. The ion 76 is attacked at carbon by acetate ion, but at sulfur by hydride ion. The reactions of sulfur dichloride with 5-exo-methylene-2-norbornene to give 53 is believed to involve an intramolecularly S-alkylated thietane. ... 

Methylene derivatives of thietanes have been obtained by the Wittig reaction of 3-thietanones, as in the preparation of 365 and the phosphonium ylide 345 with p-nitrobenzaldehyde (to give 354). A Wittig reaction also has been applied to a 2-thietanone. ... 

The similarity in the reactivities of free ions and corresponding ion pairs derived from the same cyclic monomer is more intriguing. Whereas ion pair reactivities are about 10 times smaller than corresponding free ion values in the anionic polymerization of vinyl monomers [39], and probably of the same relative proportions in cationic systems, the difference in cationic ring opening polymerizations is considerably less. For polymerization of THF in methylene chloride the factor is only 7, and for polymerization of 3,3-dimethylthietan, 40 in methylene chloride and 1 in nitrobenzene. Because the overall reactivity in cyclic monomer reactions is lower than for olefinic polymerizations, it might be expected that difference between free ion and ion pair reactivities, within one system, would also be less. However, this does not seem to be the whole answer. Plesch [44] has pointed out that in the polymerization of cyclic ethers and thietans (and presumably, therefore, other cyclic monomers)... 

Higher conversions in thiirane polymerizations, however, proceed with chain scission transfer mechanism under the influence of BF3 (C2H5)20 [192]. This is indicated by a change in the molecular weight distribution, a bimodal character. When the reaction is complete there is a marked decrease in the average molecular weight of the polymer. When thietane polymerizes with triethyl-oxonium tetrafluoroborate initiation in methylene chloride, the reaction terminates after only limited conversion [193]. This results from reactions between the reactive chain ends (cyclic sulfonium salts) and the sulfur atoms on the polymer backbone. In propylene sulfide polymerization, however, terminations are mainly due to formations of 12-membered ring sulfonium salts from intramolecular reactions [193]. 

Thiobarbiturates (59) undergo (2-i-2)-cycloaddition with alkenes to give the thietanes (60) and the methylene derivatives (61) by secondary photolysis involving ehmination of either thioacetone or thio-formaldehyde (Scheme 8). > Dithiobarbiturate and trithiobarbiturate undergo analogous reactions. 

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