The effects of C–S and C–Se bonds on torquoselectivity: stereoselective olefination of α-thio and α-selenoketones with ynolates

Highly Z-selective olefination of acyclic α-thio and α-selenoketones with ynolates has been achieved, and the theoretical calculations of the transition states in the ring-opening of the intermediates, the β-lactone enolates, revealed that the torquoselectivity was controlled by the secondary orbital interactions between the σ orbital of the C–S bond or a lone pair orbital on the S and σ∗ orbitals of the breaking C–O bond, and the σ orbital of the breaking C–O bond or a lone pair orbital on the O on the ring and the σ∗ orbitals of the C–S bond. The synthetic applications of the resulting olefins are also shown.