Prochiral unsaturated carboxylic acid

Prochiral unsaturated carboxylic acids present an anomaly, since some of the best examples of their asymmetric hydrogenation require monophosphine-derived catalysts. An early example using Morrison s neomenthyldiphenylphosphine, (35), is shown and in a wide-ranging study respectable optical yields were obtained. In reduction of (36) and... 

Prochiral organic acids were hydrogenated on clay-supported Rh-chiral phosphine complexes.205,206 Hectorite-supported chiral Rh(I)-phosphine complexes were used for the asymmetric hydrogenation of a,P-unsaturated carboxylic acids.207 It was found that the interaction between the a-ester group of itaconates and phenyl groups of phosphine can play an important role in the determination of the configuration of products. 

BINAP was first introduced by Noyori [80]. It has been particularly explored for reduction with ruthenium catalysts. BINAP is an atropisomeric ligand because rotation aroimd the central C-C bond is blocked. Accordingly BINAP exists in two enantiomers. Complexes of Ru(II) with BINAP are extremely powerful catalysts for enantioselective hydrogenations of prochiral a,p- and P,Y-unsaturated carboxylic acids, enamides, allylic and homoallylic alcohols, imines etc. [83]. In many cases, the hydrogenation is quantitative with enantiomeric excesses of over 95%. A wide variety of vitamins, terpenes, P-lactam antibiotics, etc. are accessible by the use of catalysts containing the BINAP stereogenic element. An example for 3-oxo carboxylic esters is shown in reaction (1) of Fig. 6.32. 

Among the carbon electrophiles, carbonyl compounds [113,114] were first applied in the reaction with lithiated ferrocenylalkyl amines (Sect. 4.S.3.3 and Fig. 4-18). Analogously, carboxylic acids are obtained from CO2 [153]. The reactivity pattern of palladated ferrocenylalkyl amines with carbon electrophiles is somewhat different. Carbon monoxide in alcohols leads to the formation of esters of substituted ferrocenecarboxylic acids [124]. With prochiral alcohols, a moderate asymmetric induction is observed [154]. a, -Unsaturated ketones react with palladated ferrocenylalkyl amines not with addition to the carbonyl group, but with substitution of a hydrogen at the carbon—carbon double bond, allowing the introduction of longer side chains at the ferrocene ring (Fig. 4-27c) [124, 152]. 

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