Metal-catalyzed rearrangements of allylic esters

It has been shown that Pd(CH3CN)2Cl2 catalyzes the rearrangement of allylic esters. Carbamates rearrange more rapidly than acetates which in turn rearrange more rapidly than carbonates. Allylic carbamates are more rapidly isomerized by Pd(CH3CN)2Cl2 than by Hg(OCOCF3)2. The rearrangement proceeds well except in cases where the central carbon of the allylic system is fully substituted.In contrast to the reported rearrangement of allylic carbamates by Hg2+ and previous reports of Pd2+-catalyzed rearrangements of allylic esters, this work showed the latter are extremely E specific; thus, E allylic acetates yield equilibrium mixtures free of Z allylic isomers, under conditions in which Z allylic acetates are unreactive. This E specificity is applied to stereospecific 1,3-diene synthesis from bis E,Z-allylic acetates.