Lewis base-catalyzed divergent isomerizations of 5-hydroxyl-2,3-dienoate

A divergent isomerization of 5-hydroxyl-2,3-dienoate 1 catalyzed by Lewis base has been developed, the phosphine catalyst leads to 5-oxohex-2(3)-enoates 2 while DABCO catalyst affords 3-ethoxy α,β-unsaturated lactone 3.