Synthesis of regioisomeric cyclopentanones 3-alkyloxy-2-oxabicyclo [3.3.0] octan-6-one (overall yield up to 34%) and 3-alkyloxy-2-oxabicyclo [3.3.0] octan-7-one (overall yield up to 18%) in four steps, starting from enantiomerically pure (-)-(1S, 5R)-2-oxabicyclo [3.3.0] oct-6-en-3-one is described.