Cascade reactions: sequential homobimetallic catalysis leading to benzofurans and beta,gamma-unsaturated esters

The concatenation between a Pd(0)-promoted deallylation catalytic cycle and a Pd(II)-promoted heterocyclization catalytic cycle (an example of what we have named “sequential homobimetallic catalysis”) has been shown to occur starting from 1- (2-allyloxyphenyl)-2-yn-1-ols 1 to afford 2-benzofuran- 2-ylacetic esters 2 and b,g-unsaturated esters in high yields under carbonylative conditions. In view of the conceptual as well as the synthetic importance of the process, the mechanistic aspects and the synthetic scope of the reaction have been investigated in detail. All the experimental evidence is in agreement with the sequential homobimetallic mechanism, and the reaction has proven to be of general synthetic applicability.