Palladium Catalyzed Alkoxycarbonylation Reactions of 2-En Carbonates

Abstract

Homogeneous catalysis relaying on transition metal complexes has led to innovation in organic chemistry. Palladium complexes are the most versatile and used extensively in organic synthesis. One type of these reactions is the carbonylation reactions with palladium complexes in the presence of alcohol and carbon monoxide. Extensive studies have been carried out on palladium-catalyzed carbonylation reactions of allylic and propargylic compounds. Alkynes containing a leaving group in propargylic position undergo alkoxycarbonylation reactions through the involvement of an σ-allenylpalladium as an intermediate to produce allenic esters. On the other hand, allylic compounds usually leads to β,γ-unsaturated esters through the involvement of a π- allylpalladium complex, when subjected to alkoxycarbonylation processes. With the high reactivity of allyl carbonates and propargyl carbonates in mind toward P(0)-catalyzed reactions, we attemped the palladium catalyzed alkoxycarbonylation reaction of Z- or E-configured 2,4-enyne carbonates leading to vinylallene ester structures. The reactions involved 1,5-type substitution and proceeded through formation of σ-vinylallenylpalladium species.