Monocyclic thiabenzenes, 1-alkyl-2-aroyl- (or 1-alkyl-2-cyano-) 4,5-dimethylthiabenzenes () are successfully synthesized by deprotonation of the corresponding thiopyranium salts () with triethylamine in ethanol. The ylide structures of are elucidated by spectral and chemical evidence. Thermal reaction of in several solvents provides S-alkyl rearranged products and ring-contracted ones, depending upon