Chiral amines using ruthenium catalyst

Scheme 2.26 DKR of chiral amines using CALB and a ruthenium catalyst.

Another often used chiral ligand is l,F-binaphthyl-2,2 -diyl-bis(phosphine), or binap.It can be built into ruthenium catalysts, which display high activities and enantio-selectivities for the hydrogenation of alkenes, amines, allylalcohols, and unsaturated carbonyls. A directing effect is observed for an a-hydroxy group in these cases. 

Trichloromethyl ketones (154) undergo smooth transfer hydrogenation in up to 98% ee, using a chiral ruthenium catalyst, to give the corresponding alcohol (155) in up to 97% yield. " Subsequent Jocic-type reaction with amines, again under mild conditions, 0 gives chiral amino-amides (156). 

Asymmetric C-H amination has progressed through the apphcation of rathenium(II) porphyrin catalysts. Che has employed fluorinated ruthenium porphyrin complexes with added AI2O3 (in place of MgO) to catalyze suifamate ester insertion (Scheme 17.31) [98]. These systems show exceptional catalyst activity (>300 turnovers) and afford product yields that are comparable to rhodium tetracarboxylate-promoted reactions. Of perhaps greater significance is that the use of the chiral rathenium complex... 

Oxidative amination of carbamates, sulfamates, and sulfonamides has broad utility for the preparation of value-added heterocyclic structures. Both dimeric rhodium complexes and ruthenium porphyrins are effective catalysts for saturated C-H bond functionalization, affording products in high yields and with excellent chemo-, regio-, and diastereocontrol. Initial efforts to develop these methods into practical asymmetric processes give promise that such achievements will someday be realized. Alkene aziridina-tion using sulfamates and sulfonamides has witnessed dramatic improvement with the advent of protocols that obviate use of capricious iminoiodinanes. Complexes of rhodium, ruthenium, and copper all enjoy application in this context and will continue to evolve as both achiral and chiral catalysts for aziridine synthesis. The invention of new methods for the selective and efficient intermolecular amination of saturated C-H bonds still stands, however, as one of the great challenges. 

An excellent review describing asymmetric transfer hydrogenation has been published156. Many excellent results have been achieved in recent studies of acrylic acid reductions employing the same catalysts of ruthenium or rhodium with a chiral diphosphine as were used in the hydrogen gas process1331157. In this case, however, the most common hydrogen source is the combination of formic acid with an amine. The choice of amine is often critical in the reduction shown in Scheme 30, the use... 

The first enantioselective alkylation of l,3-diphenylprop-2-enyl ethylcarbonate 19 with sodio dimethyl malonate using a ruthenium-based catalyst has been reported [113]. As shown in Eq. 2, a planar-chiral cyclopentadienylruthenium complex 35 catalyses the addition in excellent yield and enantioselectivity. The complex also catalyzed the amination although in lower ee (74%). Other derivatives of the complex also gave excellent results. Interesting selectivity (90-95% ee) has been obtained with platinum complexes though the conversions are low (25-39%) [114,115]. 

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