Asymmetric synthesis by metal BINAP catalysts

Abstract

This article covers catalytic asymmetric syntheses effected by BINAP ( R or S 2,2′-diphenylphosphino-1,1′-binaphthyl) ligand. The atropisomeric ligand is outstanding in its extremely high enantioselective recognition of hydrogen, when coordinated to rhodium or ruthenium metal. A unique chiral multiplication (asymmetric catalysis) derived from the isomerization of allylic amines to enamines by Rh-BINAP catalysis is reviewed from discovery to industrialization. The catalyst converted isoprenoid allylic amine to citronellal enamine in perfect selectivities (99% yield and 98% enantiomer excess) and activity (TON > 400 000) that promised the commercial manufacturing of enantiomerically pure terpene aldehydes. The industrial application of the highly sensitive and expensive Rh-BINAP catalyst for the production of 1500 t/y scale of chiral terpene compounds is introduced with some technical know how. A series of new ruthenium BINAP complexes was prepared and evaluated for asymmetric hydrogenation. Neutral Ru-BINAP dicarboxylato complexes catalyzed the hydrogenation of activated carbon-carbon double bonds enantioselectively. Prochiral unsaturated substrates including α-(acylamino)acrylic acids, allylic alcohols, α,β-unsaturated carboxylic acids and cyclic enamides were easily reduced to give saturated products in quantitative yields with 90–99% enantiomer excesses. Cationic Ru-BINAP complexes catalyzed the hydrogenation of functionalized ketones enantioselectively. Prochiral ketones bearing hetero atom-containing functional groups at α,β or γ position were smoothly reduced affording corresponding alcohols in quantitative yields with high enantiomeric excesses. Industrial applications of these methodologies for pharmaceuticals and new materials are summarized.