Tandem Henry/oxa-Michael route to the 1,3-disubstituted-1,3-dihydrobenzo[c]furan system

The reaction of ortho-formyl cinnamates and ortho-formyl-α-benzalketones with suitably substituted alkylnitro compounds in the presence of 1,1,3,3-tetramethylguanidine results in the formation of 1,3-disubstituted dihydroisobenzofurans. The reaction mechanism entails a base-mediated nitronate addition to the aryl formyl group followed by intramolecular alcoholate addition to the unsaturated component that then affords the isobenzofuran system.