Regioselective synthesis of functionally hindered α-methylstyrenes through ring transformation of 2H-pyran-2-ones with mesityl oxide

A regioselective synthesis of α-methylstyrenes with electron-withdrawing or -donating substituents is described and illustrated by carbanion-induced ring transformation of 2H-pyran-2-one with mesityl oxide in excellent yield. The potential of the reaction lies in the creation of an aromatic ring possessing an isopropenyl unit from six-membered lactones at room temperature under mild reaction conditions.