Stereoselective Olefination of Unfunctionalized Ketones via Ynolates

摘要

Ynolates react with ketones at room temperature to afford α, β, β-trisubstituted acrylates (tetra-substituted olefins) with 2:1―8:1 geometrical selectivities. This can be regarded as a new olefination reaction of ketones giving tetrasubstituted olefins in good yield, even in the case of sterically hindered substrates. The reaction mechanism involves cycloaddition of ynolates with a carbonyl group and subsequent thermal electrocyclic ring-opening of the resulting β-lactone enolates. The stereoselec-tivity is determined in the ring-opening, which is regulated by torquoselectivity. In this paper, we describe the scope and limitations of olefination of ketones via ynolates and discuss the stereocontrol mechanism.