(E)-2-boryl 1,3-dienes from the 10-TMS-9-BBDs: highly selective reagents for the asymmetric synthesis of anti-α,β-disubstituted β-allenylamines from the allylboration of aldimines

Abstract

The asymmetric allylboration of N-H aldimines with optically pure trans-4-substituted-2-boryl-1,3-dienes 6 is described. These organoboranes 6 serve as near-perfect asymmetric allylborating agents for N-H aldimines for the preparation of anti-1,2-disubstituted-3,4-pentadien-1-amines 11 as essentially single diastereomers in enantiomerically pure form (>98% de, ≥98% ee). Enantiomerically pure cis-2,3-disubstitued piperidines 12 and α,β-disubstituted-β-amino acids 17 are readily prepared through the standard protocols. A novel Ru-catalyzed hydroamination provides trans-4,5-disubstituted-1-pyrrolines 21 from 11.