Cooperative Carbene Photocatalysis for β-Amino Ester Synthesis
Nao Tanaka, Joshua L. Zhu, Oniya L. Valencia, Cullen R. Schull, Karl A. Scheidt
Abstract
β-Amino acids are useful building blocks of bioactive molecules, including peptidomimetics and pharmaceutical compounds. The current limited accessibility to β 2,2 -type amino acids which bear an α-quaternary center has limited their use in chemical synthesis and biological investigations. Disclosed herein is the development of a new N-heterocyclic carbene/photocatalyzed aminocarboxylation of olefins, affording β 2,2 -amino esters with high regioselectivity. The generation of nitrogen-centered radicals derived from simple imides via a sequence of deprotonation and single-electron oxidation allows for the subsequent addition to geminal-disubstituted olefins regioselectively. The intermediate tertiary radicals then cross-couple with a stabilized azolium-based radical generated in situ to efficiently construct the quaternary centers. Mechanistic studies, including Stern–Volmer fluorescence quenching experiments, support the proposed catalytic cycle.