Cyclic sulphones. Part XVIII. Probes for conjugation of the sulphonyl group: thiopyrano[3,2-b]quinoline 1,1-dioxides

Abstract

Three N-methyl-3-phenyl-5H-thiopyrano[3,2-b]quinoline 1,1-dioxides have been synthesized; the parent compound underwent bromination, nitration, azo-coupling, and Vilsmeier reaction in the thiopyran residue. Moderate bathochromic displacements of the sulphonyl stretching vibrations relative to normal values were observed. The results are discussed in the light of a preliminary X-ray report: it is concluded that in the title compounds ‘one-side’ conjugation of the sulphonyl group occurs without involvement of the sulphur–oxygen bonds. Structural analogies conferred on similar cyclic unsaturated frameworks by incorporation of sulphonyl and carbonyl groups are also discussed.