Synthesis of 3-alkylidene-2,2,4,4-tetramethylthietan 1,1-dioxides, possible precursors of 2-methylenetrimethylene
Abstract
The title compounds (Va–c) may be synthesised by the reaction of 2,2,4,4-tetramethylthietan-3-thione 1,1-dioxide (VIIb) with diazoalkanes and treatment of the resultant spirothiirans (Xa–c) with triphenylphosphine. Flash vacuum pyrolysis (770 °C) of the isopropylidene compound (Va) gives almost exclusively 3-isopropyl-2,4-dimethylpenta-1,3-diene (XI). This is consistent with the formation of an intermediate 2-methylenetrimethylene diradical (XIII), although other intermediates cannot be excluded.