Journal of the American Chemical Society, Vol.136, No.52, 17966-17968, 2014
Highly Enantioselective, Intermolecular Hydroamination of Allenyl Esters Catalyzed by Bifunctional Phosphinothioureas
Bifunctional phosphinothiourea catalysts have been developed successfully for the highly regio- and enantioselective gamma-hydroamination of allenyl and propargyl esters with N-methoxy carbamate nucleophiles to yield alpha,beta-unsaturated gamma-amino acid ester products. In the case of propargyl ester substrates, the reaction proceeds through reversible phosphinothiourea-catalyzed isomerization to the corresponding allenyl ester. The high enantioselectivity of the process is attributed to a cooperative conjugate addition of a thiourea-bound carbamate anion to a vinyl phosphonium ion resulting from covalent activation of the allenyl ester substrate.