Selective Stobbe condensation under solvent-free conditions

Solvent-free condensation of cyclohexanone (1) and diethyl succinate (2) in the presence of (BuOK)-O-t at room temperature gives cyclohexylidenesuccinic acid (3), while heating a mixture of 1, 2 and (BuOK)-O-t at 80 degreesC gives only cyclohexenylsuccinic acid (4).