A novel tandem reaction of 3-substituted coumarins with two equivalents of dimethylsulfoxonium ylide to 2-substituted cyclopenta[b]benzofuran-3-ol derivatives

When the coumarins () having an electron-withdrawing group at the 3 position were treated with 2.4 equiv. of dimethylsulfoxonium methylide at room temperature in DMF or DMSO, novel tricyclic 2-substituted cyclopenta[b]benzofuran-3-ols () were obtained in moderate to good yields. The intermediates, 1a-substituted benzo[b]cyclopropa[d]pyran-2(1aH)-ones (), of this tandem reaction were isolated and derived to the corresponding 2-substituted cyclopenta[b]benzofuran-3-ols () by treatment with 1.1 equiv. of dimethylsulfoxonium methylide.