Cyclic sulphones. Part XVI. Probes for conjugation of the sulphonyl group: thiopyranylidenedihydropyridine SS-dioxides

The thiopyran group in the title compounds (7)–(10), which have been synthesized, may represent a reasonable model for the thiopyran SS-dioxide anion. Dipolar forms contribute to the ground state of these compounds as shown by 1H n.m.r. correlations and from reactions with electrophiles. I.r. stretching vibrations of the sulphonyl group of these molecules show considerable bathochromic displacements relative to the standard values, indicating that the sulphonyl group encounters the most favourable conditions for case I conjugation.