Phosphine-Catalyzed Synthesis of Diquinanes

Significance

Fu and co-workers report the tri-n-butylphosphine-catalyzed cyclization of ynone enoates 1 to the corresponding diquinanes 2. The products were obtained in good to high yields and outstanding diastereoselectivities. A plausible mechanism involves the conjugate addition of the phosphine to 1, followed by tautomerization. The generated enolate undergoes a conjugate addition to the enoate, before a second Michael-type addition and subsequent elimination furnishes the desired product 2. Alternatively to this stepwise mechanism a [3+2]-dipolar cycloaddition can be considered, forming both rings and all new stereocenters at the same time. Besides the high functional group tolerance, further derivatizations of the products, the construction of 6,5-ring systems and a promising approach towards a catalytic asymmetric version of this reaction are additionally provided.