Enantioselective Bronsted acid catalysts

Examples of the Bronsted-acid catalysts and hydrogen-bond catalysts are shown in Figure 2.1. We have recently reported the Mannich-type reaction of ketene silyl acetals with aldimines derived from aromatic aldehyde catalyzed by chiral phosphoric acid 7 (Figure 2.2, Scheme 2.6) [12]. The corresponding [5-amino esters were obtained with high syn-diastereoselectivities and excellent enantioselectivities. 

Enantioselective Synthesis of Amines by Chiral Bronsted Acid Catalysts... 

In this chapter, we focus on recent achievements in the enantioselective synthesis of chiral amines using 1,1 bi 2 naphthol (BINOL) derived monophosphoric acid (1) or related phosphoric acids as chiral Bronsted acid catalysts 2, 3], The contents are arranged according to the type of bond forming reaction, including carbon carbon, carbon hydrogen, and carbon heteroatom bond forming reactions, followed by specific reaction types. 

Structural motif of chiral Bronsted acid catalysts. Further modification of the chiral diamine backbone or the substituents on the nitrogen atoms of the catalyst could lead to its becoming an efficient enantioselective catalyst. 

Phosphoric acids 32 and 35 have been successfully employed as chiral Bronsted acid catalysts for vinylogous Mannich reactions of acyclic silyl dienolates with imines (Table 5.5 and Scheme 5.10). Why does the exchange of a para methyl group for a tert butyl group on the 3,3 aryl groups within the BINOL backbone have such a pronounced effect on the enantioselectivity of the reaction although this position appears to be quite remote from the reaction center ... 

The catalyst (99) has also been used for the enantioselective transfer hydrogenation of a,P-unsaturated ketones (Scheme 32)7 Aldimines (100) undergo aza-Diels-Alder reactions with Brassard s diene (101) in the presence of a chiral cyclic phosphate pyridinium salt (102) as a Bronsted acid to give a,P-unsaturated 5-lactams (103, Ar = 2-(p-cresol)) with excellent enantioselectivity (Scheme 33)7 Highly reactive and acidic chiral Bronsted acid catalyst, chiral iV-triflyl... 

The new bidentate phosphoramide (106) derived from 2,2-bispyrrolidine provided the highest yield and enantioselectivity in the addition of various allylic trichlorosilyl species to aromatic and unsaturated aldehydes (Scheme 36). It has been shown that phosphorodiamidic acid is a novel structural motif of Bronsted acid catalysts (107)... 

Terada, M. Tanaka, H. Sorimachi, K. Enantioselective Direct Aldol-Type Reaction of Azlactone via Protonation of Vinyl Ethers by a Chiral Bronsted Acid Catalyst. /. Am. Chem. Soc. 2009,131,3430-3431. 

On the other hand, several groups have also recently developed asymmetric domino reactions through relay catalysis with combinations of organocatalysts with ruthenium catalysts. For example. You et al. demonstrated in 2009 that ruthenium catalyst could be compatible with Bronsted acid catalyst. They reported a practical and economical synthesis of chiral tetrahydropyrano[3,4-b]indols and tetrahydro-p-carbolines by the combination of ruthenium-catalysed olefin cross-metathesis and a chiral phosphoric acid-catalysed Friedel-Crafts alleviation reaction, as shown in Scheme 7.41. This domino reaction allowed the use of readily available materials to highly enantioselectively construct synthetically valuable polycyclic indole frameworks in enantioselectivity of up to 94% ee. 

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