4-(Dimethylamino)pyridine as a catalyst for the lactonization of 4-hydroxy-2-methylenebutanoate esters

The catalytic action of 4-(dimethylamino)pyridine (DMAP) in lactonizing 4-hydroxy-2-methylenebutanoate esters to 2-methylene-γ-butyrolactones is described. The use of DMAP, which functions as an excellent complement to the more traditional acid-catalyzed lactonization protocol, allows for the synthesis of 2-methylene-γ-butyrolactones containing acid-sensitive groups under essentially neutral conditions.