Annulation of quinone methides with 2-benzylidene dithiolanes: synthesis of spirochroman dithiolanes.

An expeditious and regioselective approach towards the construction of a spiro-chroman motif is described. Quinone methides underwent a PTSA catalyzed annulation with 2-benzylidene dithiolanes to afford spiro-chroman dithiolanes in high yields. The synthetic versatility of the dithiolane motif was demonstrated by converting the adduct to coumarin, 3,4-dihydrocoumarin and chroman derivatives.