Susumu Akutagawa

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.

Enantioselective isomerization of allylamine to enamine: practical asymmetric synthesis of (–)-menthol by Rh–BINAP catalysts

Enantioselective isomerizations of allylamines to enamines are summarized from idea to industry. The Rh–BINAP catalyst reveals high selectivities, 99% yield and 98% enantiomer excess and high activity, TON > 400,000. Its industrial use for the production of a 1,500 t/y scale of (–)-menthol is introduced emphasizing technical development.