Noncovalent Bifunctional Organocatalysis Mediated by β-Amino Alcohols

Abstract

Chiral compounds, bearing closely positioned Bronsted base and Bronsted acid groups, are usefully exploited as bifunctional organocatalysts in a wide array of asymmetric processes. These compounds operate via the generation of a more active nucleophilic species through general base catalysis, whereas the electrophile is activated via hydrogen bonding by the Bronsted acidic group. In this review, we illustrate the achievements appeared in the literature after 2001 up to early 2010, with a focus on reactions mediated by organocatalysts bearing the β-amino alcohol core as their catalitically active site. 1,2-Additions, ring-closure reactions, conjugate additions, α- functionalization of carbonyl compounds are efficiently accomplished by β-amino alcohols as catalysts. Most of the processes described are promoted by cinchona alkaloids, whereas some examples include the use of L-proline derivatives such as α,α-diaryl prolinols. The ready availability of β-amino alcohols from the chiral pool, makes them an appealing class of versatile promoters to exploit in modern organic synthesis. Keywords: β-amino alcohols, enantioselective organocatalysis, noncovalent catalysis, cinchona alkaloids, α,α-diaryl prolinols, carboncarbon bond forming reactions, carbon-heteroatom bond forming reactions, L-proline derivatives, phase transfer catalysis (PTC), amino alcohol portion, (CHP) cumyl hydroperoxide, (PEG) polyethylene glycol, MANNICH REACTIONS, FRIEDEL-CRAFTS REACTIONS, CONJUGATE ADDITIONS