Addition/ring-opening reaction of organoboronic acids to cyclobutanones catalyzed by rhodium(I)/P(t-Bu)3 complex

An addition/ring-opening reaction of aryl- and alkenylboronic acids to cyclobutanones took place in 1.4-dioxane at 100 degrees C in the presence of a rhodium(I) catalyst bearing tri-t-butylphosphine, affording ring-opened ketones, Mechanistically, the reaction proceeded through the addition of an organorhodium species to the carbonyl group of a cyclobutanone and a subsequent ring-opening of the resulting rhodium cyclobutanolate through carbon elimination. A deuterium-labeling experiment revealed that an alkylrhodium species generated by the beta-carbon elimination underwent successive beta-hydride elimination/re-addition processes to form the eta(3)-oxaallylrhodium intermediate, which was readily protonated to afford the product.