o-quinodimethanes from 3,6-dihydrobenzo[b]-1,2-oxathiin-2-oxides

A two step synthesis of 3,6-dihydrobenzob]-1,2-oxathiin-2-oxide 5a from o-tolual-dehyde via the photochemically produced 1-hydroxy-1,3-dihydrobenzob]thiophene-2,2-dioxide is described. Analogous syntheses of 3 and 6 substituted derivatives of the benzosultines 5 have also been carried out. The feasibility of using these benzosultines as o-quinodimethane precursors has been tested by thermalizing the phenyl sultine 5c in refluxing cyclohexane in the presence of dimethyl fumarate, dimethyl maleate and methyl crotonate to form cycloadducts, stereospecifically and in good yield. The stereochemistry of addition of maleate appears to be exclusively “exo” in conflict with earlier studies on Diels-Alder reactions of α-aryl-o-quino-dimethanes.