In recent years, organocatalysis has enhanced its importance as a tool for the synthesis of enantiomerically enriched compounds. Among the candidates for organocatalysis, the construction of asymmetric quaternary carbons is regarded as a challenging problem in organic synthesis. In particular, 3,3′-disubstituted oxindoles have one or more asymmetric quaternary carbon atoms and they represent a large family of bioactive compounds and synthetic derivatives that mimicry natural products. Therefore they are good targets for drug candidates and in the last two years many papers have appeared on organocatalytic methods for the synthesis of 3,3′-disubstituted oxindoles. Moreover, in the last few years 2-substituted and 2,2′-disubtituted 3-indolinones have also attracted the interest of chemists. This review aims to cover the literature on these topics from its origin to the end of 2011.
The desire for new synthetic methodologies for the rapid construction of enantiomerically pure substituted indole has been a fruitful driving force for chemical research in the last few years. This research line has produced a stunning array of enantioselective technologies either metal or organocatalyzed. This critical review documents the development of organocatalytic indole alkylation strategies, until the end of 2009 (127 references).
9 September 2009 in Angewandte Chemie International Edition
In spite of the many catalytic methodologies available for the asymmetric functionalization of carbonyl compounds at their α and β positions, little progress has been achieved in the enantioselective carbon–carbon bond formation γ to a carbonyl group. Here, we show that primary amine catalysis provides an efficient way to address this synthetic issue, promoting vinylogous nucleophilicity upon selective activation of unmodified cyclic α,β-unsaturated ketones. Specifically, we document the development of the unprecedented direct and vinylogous Michael addition of β-substituted cyclohexenone derivatives to nitroalkenes proceeding under dienamine catalysis. Besides enforcing high levels of diastereo- and enantioselectivity, chiral primary amine catalysts derived from natural cinchona alkaloids ensure complete γ-site selectivity: The resulting, highly functionalized vinylogous Michael adducts, having two stereocenters at the γ and δ positions, are synthesized with very high fidelity. Finally, we describe the extension of the dienamine catalysis-induced vinylogous nucleophilicity to the asymmetric γ-amination of cyclohexene carbaldehyde.