Enantioselective Borohydride Reduction of N-Diphenylphosphinyl Imines Using Optically Active Cobalt(II) Complex Catalysts

Abstract

The enantioselective borohydride reduction using optically active cobalt(II) complex catalysts was successfully applied to various aryl N-diphenylphosphinyl imines, and the corresponding reduced products were obtained in good yields with high enantiomeric excesses (up to 99% ee). The optically active primary amines were obtained by the successive hydrolysis under mild conditions.

Enantioselective Reduction of Ketones and Imines Catalyzed by (CN‐Box)ReV–Oxo Complexes

“…The phosphinyl group can easily be cleaved under acidic conditions to yield the chiral amine. [xxxii] …”

Studies on the Bisoxazoline‐ and (−)‐Sparteine‐Mediated Enantioselective Addition of Organolithium Reagents to Imines

“…Although excellent reviews are available, [2] seminal contributions from Mukaiyama (cobalt), [3] Burk (rhodium), [4] Buchwald (titanium), [5] Noyori (ruthenium),[6] Pfaltz (iridium), [7] Lipshutz (copper)8 Toste (rhenium) [9]should be noted.…”

Asymmetric Reduction of Ketones Under Mild Conditions Using NaBH4 and TarB‐NO2: An Efficient and Unusual Chiral Acyloxyborohydride Reducing System

“…(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) cently, Mukaiyama has developed a catalytic system utilizing alcohol-modified NaBH 4 combined with a catalytic amount of a chiral β-ketoiminato cobalt() complex to provide high ee values for the reduction of a number of prochiral ketones and imines at reduced temperatures. [13][14][15] Interestingly, while the use of NaBH 4 with achiral carboxylic acids is well established as an efficient achiral reducing system, the application of chiral carboxylic acids with NaBH 4 for the asymetric reduction of ketones has not been thoroughly investigated.…”