On the mechanism of DABCO-catalyzed isomerization of gamma-hydroxy-alpha,beta-alkynoates to gamma-oxo-alpha,beta-(E)-alkenoates.

[reaction: see text] Since the discovery of organic base-catalyzed isomerization of gamma-hydroxy-alpha,beta-acetylenic esters to gamma-oxo-alpha,beta-trans-alkenyl esters in 1949, the mechanism has not been elucidated. This study shows that the mechanism involves cumulene formation, protonation with the conjugate acid of the amine, and protonation of the resulting allenol with water.