Synthesis and thermal Reactions of Cyano-Stabilized Cyclic Sulfur Ylides, 2-Alkyl-1-cyano-3, 4-dihydro-1H-2-thionianaphthalen-1-ides

1-Cyanoisothiochromans 4 were synthesized by the intramolecular Pummerer reaction of cyanomethyl phenethyl sulfoxides 3 with trifluoroacetic anhydride. Alkylation of the isothiochromans 4 afforded isothiochromanium salts 5 which consist of cis- and trans-isomers. 1-Cyano-2-methyl-3, 4-dihydro-1H-2-thionianaphthalen-1-ides 6 were prepared by deprotonation of 5 with triethylamine or sodium hydride. Thermal reaction of the ylide 6a in benzene or N, N-dimethylform-amide gave the 1, 2-rearranged product 7 accompanied with the dimers 8, whereas the reaction in acetonitrile gave the dimers E-8 (8-I) (31.6%) and Z-8 (8-II) (22.6%) as the major products. The geometrical structures of 8 were determined by infrared (IR) and Raman spectroscopy. The dimers 8 were formed at room temperature by treatment with tetracyanoethylene or 7, 7, 8, 8-tetracyano-quinodimethane. Unexpected products, 1-benzylated isothiochromans 10, were obtained upon heating 6a in toluene and its derivatives. A reaction mechanism involving the benzyl radicals was postulated for this novel solvent-uptake reaction.