Reaction of dimethoxycarbene-DMAD zwitterion with 1,2-diones and anhydrides: A novel synthesis of highly substituted dihydrofurans and spirodihydrofurans

[GRAPHICS] The zwitterion formed by the reaction of dimethoxycarbene and DMAD adds efficiently to one of the carbonyl groups of 1,2-dicarbonyl compounds and anhydrides to generate dihydrofurans and spirodihydrofurans in good yields. In many cases, the carbene inserts into the C-C bond of the dione to yield masked vicinal tricarbonyl systems.