A new entry to carbocycles: synthesis of cyclopentene and cyclohexene derivatives through endo-mode ring closure of allenyl sulfones

Treatment of dimethyl 4-(phenylsulfonyl)-4,5-hexadiene-1,1-dicarboxylate with potassium tert-butoxide in tert-butanol at room temperature effected successive endo-mode ring closure at the sp-hybridized carbon center and demethoxycarbonylation of the resulting malonate derivative leading to the exclusive formation of methyl 2-methyl-3-(phenylsulfonyl)-1-cyclopentenecarboxylate. An additional seven allenyl sulfones having a 1,3-dicarbonyl functionality gave the corresponding cyclopentene or cyclohexene derivatives in high yields.