Synthesis and Suzuki-Miyaura Cross-Coupling of Enantioenriched Secondary Potassium β-Trifluoroboratoamides: Catalytic, Asymmetric Conjugate Addition of Bisboronic Acid and Tetrakis(dimethylamino)diboron to α,β-Unsaturated Carbonyl Compounds.

Abstract

Enantioenriched potassium β-trifluoroboratoamides have been synthesized via an asymmetric, copper-catalyzed 1,4-addition of tetrahydroxydiboron (BBA) and tetrakis(dimethylamino)diboron to α,β-unsaturated amides. These dibora reagents provide access to the desired organotrifluoroborates using effective and atom economical sources of boron. The copper-catalyzed β-boration is extended to α,β-unsaturated ketones and esters. Desired potassium organotrifluoroborates are synthesized with yields up to 92% and enantiomeric ratios up to 98:2. The enantioenriched potassium β-trifluoroboratoamides are successfully cross-coupled with an array of aryl and heteroaryl chlorides in high yield with complete stereochemical fidelity as the transmetalation proceeds through an SE2 mechanism via an open transition state.