Photocatalyzed, Beta-Selective Hydrocarboxylation Of Alpha,Beta-Unsaturated Esters With Co2 Under Flow For Beta-Lactone Synthesis

A photocatalyzed, beta-selective hydrocarboxylation of alpha,beta-unsaturated esters employing CO2 radical anion generated under flow conditions was developed. A range of substrates bearing a variety of functional groups were tolerated, demonstrating chemoselectivity. A series of quaternary carboxylic acids were obtained from sterically demanding beta,beta-disubstituted alkenes including those derived from natural products. Mechanistic studies support a Giese-type CO2 radical anion conjugate addition followed by hydrogen atom transfer from (TMS)(3)SiH as the principal reaction pathway. Finally, a telescoped process involving the described beta-carboxylation followed by a alpha-bromination/beta-lactonization sequence provides a strategy for beta-lactone synthesis.