Asymmetric NaBH₄ 1,4‐Reduction of C3‐Disubstituted 2‐Propenoates Catalyzed by a Diamidine Cobalt Complex

Abstract

Abstract A new Co complex of a unique diamidine ligand catalyzes asymmetric NaBH 4 reduction of C3‐disubstituted ( E )‐ and ( Z )‐2‐propenoates, including C3‐oxygen‐ and nitrogen‐substituted substrates with high enantioselectivity. Analysis by X‐ray diffraction, 1 H NMR spectroscopy, ring‐opening radical‐clock and D‐labeling reactions, and the structure/selectivity relationship suggest that a mechanism of CoH‐involved non‐single‐electron transfer 1,4‐addition differentiates the C2 enantioface. Involvement of CoH species has been supported by quantitative isolation of a new type of CoH 2 (BH 3 ) 2 complex.