Heterocycles by cycloaddition. Part 5. Preparation of 7,9-diheteratricyclo[4.2.1.02,5]non-3-en-8-one derivatives from mesoionic compounds

Abstract

Cycloaddition of a mesoionic dithiolone or thiazolone (1) with dimethyl tricyclo[4.2.2.02,5]deca-3,7,9-triene-7,8-dicarboxylate (2) occurred at the cyclobutene ring. Thermal fragmentation of the adducts (3) or the corresponding S-oxides (6) gave dimethyl phthalate and the title diheteratricyclononenone derivatives (4) or their S-oxides (7).