Synthesis and thermal transformation of stable monocyclic lambda(4)-thiabenzenes

The stable monocyclic lambda (4)-thiabenzenes 6a-e, which are stabilized wi th electron-withdrawing substituents such as benzoyl, cyano and alkoxycarbo nyl groups, are synthesized in high yields by proton abstraction from the c orresponding thiopyranium salts 5a-e with triethylamine in ethanol. The yli dic properties of the lambda (4)-thiabenzenes are established based on spec tral and chemical evidence. Thermal decomposition of the lambda (4)-thiaben zenes affords alkyl-rearranged products 7, 8, and 9, thienofuran derivative s 10 (from benzoyl-substituted lambda (4)-thiabenzenes), and thiophene deri vatives 11. A plausible mechanism for the formation of those products is al so discussed.