Prolines Brpnsted acid catalysts

S.C. PanandB. List s paper spans the whole field of current organocat-alysts discussing Lewis and Brpnsted basic and acidic catalysts. Starting from the development of proline-mediated enamine catalysis— the Hajos-Parrish-Eder-Sauer-Wiechert reaction is an intramolecular transformation involving enamine catalysis—into an intermolecular process with various electrophilic reaction partners as a means to access cY-functionalized aldehydes, they discuss a straightforward classification of organocatalysts and expands on Brpnsted acid-mediated transformations, and describe the development of asymmetric counteranion-directed catalysis (ACDC). 

Further extent of asymmetric Sjvl a-alkylation methodology to ketone motifs was disclosed by Cheng and co-workers [129] in 2010. They described the first asymmetric catalytic direct a-alkylation of cyclic ketones catalyzed by functionalized chiral ionic liquids, namely proline-derived catalyst containing benzoimida-zolium moiety (LXI, Figure 8.1), and Brpnsted acid (TFA or phthalic acid). Moreover, described catalytic system enables asymmetric desymmetiization of 3-and 4-substituted cyclohexanones to afford 2,4-trans- and 2,5-cis-substituted products, respectively, with up to 99% yield, greater than 99 1 dr and good enantioselectivities (up to 87% ee). 

More recently, it has been reported that primary amines derived from cinchona alkaloids [75] as well as proline derivatives [76], combined with achiral Brpnsted or Lewis acids, may also efficiently catalyze the enantioselective Biginelli reaction. Alternatively, a carbohydrate-based bifnnctional primary amine-thiourea catalyst was developed for this transformation, with similar enantiocontrol [77]. 

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