Hydroxide displacement of the sulfone linkage in thioxanthen-9-one 10,10-dioxides to benzophenone-2'-hydroxy-2-sulfinic acids. Intramolecular cyclization to xanthones

Abstract

2-H, 2,6-diCOOH, 2-CH_3, 2-CH_3O, and 2-NO_2 thioxanthen-9-one 10,10-dioxides were synthesized and treated, at reflux, with 2% NaOH-65% dioxane-H_2O. For these systems, facile hydroxide displacement of the sulfone linkage was found to occur exclusively on the more electrophilic ring to give the novel benzophenone-2’-hydroxy-2-sulfinic acids. Further, in alkaline media, these sulfinic acids generally undergo unique intramolecular cyclization to xanthones. The structures of the sulfinic acids were established by replacement of the sulfinic acid group with a chloromercury group followed by replacement of the latter with hydrogen to afford 2-hydroxybenzophenones.