Cyclocondensation of alicyclic and heterocyclic α-hydroxy β-dicarbonyl compounds with dimethyl malonate gives bicyclic butenolide derivatives. The reaction sequence is catalyzed by 4-( N , N -dimethylamino)pyridine and consists of two processes: Knoevenagel condensation followed by transesterification. Depending on the chemical nature of the β-dicarbonyl moiety (oxoester, diketone or α-acetyl lactone