Chiral Bronsted acid catalysts

Scheme 10 Plausible catalytic mechanism for alkyne-carbonyl coupling as supported by the effect of chiral Bronsted acid catalyst and deuterium-labeling...

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

The desirable features of phosphoric acids as chiral Bronsted acid catalysts are summarized as follows (Figure 3.1) ... 

Figure 3.1 Chiral phosphoric acids as 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. 

In general, a Lewis acid catalyzed 1,3 dipolar cycloaddition reaction of nitrones with vinyl ethers provides exo isomers predominantly. In fact, the MeAl BINOL catalyzed cycloaddition reaction of ethyl vinyl ether with diaryl nitrone furnished the corresponding product vhth high exo selectivity [121]. However, phosphoramide 6b as the chiral Bronsted acid catalyst exhibited high e-ndo selectivity in the same cycloaddition reaction (see Scheme 3.27). 

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 ... 

Some of the seminal studies of organocatalysts have been described, focusing on chiral Bronsted acid catalysts. Because this review is not comprehensive, there are a number of topics not covered in this chapter, such as carbene catalysts, bifunctional catalysts, and so on. 

Scheme 24.1b) for this reason these catalysts are often defined as hydrogen-bonding catalysts or chiral Bronsted-acid catalysts . ... 

A catalytic as5mmetric Pictet-Spengler reaction has been developed. This process furnishes enantioenriched tetrahydro-P-carbolines (88) from various tryptamines and both aromatic and aliphatic aldehydes if treated with chiral Bronsted acid catalyst (89) (Scheme 25). ... 

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... 

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. 

Ishihara and Yamamoto designed a Bronsted acid assisted chiral Bronsted acid catalyst (40), bearing a bis (trifly l)methyl group (Figure 2.31) [152]. The enantios-elective Mannich-type reaction of ketene silyl acetals with aldimines catalyzed by (40) in the presence of stoichiometric achiral proton source gave (S)-P-amino esters in high yields with good enantiomeric excesses. 

---