Studies of ring-closing mode of 4-hydroxy-2-vinylidenebutanoates: 5-exo-trig versus 5-endo-dig

The ring-closing mode (5-exo-trig vs 5-endo-dig) of benzyl 4-hydroxy-2-vinylidenebutanoates could precisely be controlled in a highly selective manner by the proper choice of conditions (solvent and base).