Thietanes ring-cleavage

Fused thiete ring systems produce the thietane cation by ring cleavage. The fragmentation pattern of these products has been established by Dittmer et... 

Treatment of 3-hydroxythietanes 21b-g with aqueous sodium hydroxide led to retro-aldol ring cleavage to produce the carbonyl derivatives 23b-g (Table 1) <1997J(P2)425>. It was proven that the rate of the reaction was determined by the nature of the substituent at the 3-position and by the oxidation state of sulfur. 3-Phenylthietane-3-ol 21b underwent retro-aldol reaction to give sulfide ketone 23b. Thietane-l-oxide-3-ol 21c-e or thietane-l,l-dioxide-3-ol 2 If and 21g derivatives underwent retro-aldol reaction to produce carbonyl sulfoxides 23c-e and carbonyl sulfones 23f and 23g (Table 1) <1997J(P2)425>. 

The proposed mechanism, which is based on the double carbonylation of styrene oxide, is shown in Scheme 6.2. The generation of an acylcobalt carbonyl complex from the reaction of cobalt tetracarbonyl anion with an alkyl halide is followed by reaction with a thiirane. This species can undergo carbonylation, the thioester function can undergo hydrolysis to reveal a sulfido nucleophile, and intramolecular cydization then produces thietan-2-one. The thietan-2-one can undergo ring cleavage and the mercapto acid results by protonahon. 

Spectra for most thietanes contain a strong parent ion peak. The four-membered ring is usually fractured into the four possible halves. For example, the cleavage of thietane derivative (43) produces peaks at mje 240, 230, 84, and 74. The parent ion peak is absent at 35°. Similarly, spirothietane 44 splits to give fragments with m/e 162 (77%), 152 (12%), 84 (100%), and 74 (0.6%). Decomposition of the thietane nucleus is also characterized by desulfurization and retro 2-1-2 cycloaddition fragments. 

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