In this Minireview recent advances in the asymmetric reactions of meso and racemic epoxides promoted by organocatalysts is reviewed. Organic promoters, such as chiral phosphoric acids, amino- and peptidyl thioureas, and sulfinamides, have been successfully used for a variety of enantioselective transformations of epoxides under catalytic conditions, involving direct nucleophilic attack at the oxirane ring, base-catalysed β-eliminations and Brønsted acid catalysed 1,2-rearrangements. Accordingly, highly valuable enantioenriched 1,2-functionalised alcohols, carbonyl compounds and nitroepoxides are attainable. Dual activation of the reagents, provided by the organocatalysts, appears to be the most recurrent strategy, potentially suitable to face other unmet challenges in asymmetric ring-opening reactions of epoxides.

[reaction: see text] An operationally simple and mild protocol for the catalytic enantioselective epoxidation of alpha,beta-unsaturated ketones has been estabilished using commercially available alpha,alpha-diphenyl-l-prolinol as bifunctional organocatalyst and tert-butyl hydroperoxide (TBHP) as oxidant. The epoxides have been obtained in good yields and with up to 80% ee.

Readily accessible alpha,alpha-diarylprolinols have been recently exploited as useful organocatalysts in different asymmetric reactions. It has been proposed that they operate either via bifunctional activation of the reactive partners through non-covalent interactions or via formation of covalent enamine and iminium intermediates. This feature article describes the employment of alpha,alpha-diarylprolinols as catalysts in the epoxidation of alpha,beta-enones, aldol reaction, cycloaddition, and carbon-carbon and carbon-heteroatom bond forming reactions.

Bishomoallylic alcohols are converted in good yields and diastereoselectivity into tetrahydrofuranols and tetrahydropyranols by Cp 2 TiCl 2 /t-butyl hydroperoxide/activated 4Å molecular sieves system.

This feature article illustrates progress in asymmetric organocatalysis achieved by using readily available α,α-L-diaryl prolinols from 2009 up to middle 2012. This class of bifunctional organocatalysts has shown the ability to catalyze a variety of reactions such as epoxidation, cyclopropanation, α-sulfenylation of active methines, cross conjugate addition, direct aldol, cycloaddition and desymmetrization reactions. The most striking feature of these promoters is to enable either non-covalent or covalent activation of the reagents, thus distinguishing themselves as a rare example of organic promoters capable of encompassing alternative mechanistic pathways, namely enamine/iminium catalysis and Brønsted acid/base catalysis.