Solvent-Induced Reversal of Enantioselectivity in the Synthesis of Succinimides by the Addition of Aldehydes to Maleimides Catalysed by Carbamate-Monoprotected 1,2-Diamines

A simple change in the polarity of the solvent allows both enantiomers of substituted succinimides to be obtained in the enantioselective conjugate addition reaction of aldehydes, mainly α,α-disubstituted, to maleimides catalysed by chiral carbamate-monoprotected trans-cyclohexane-1,2-diamines. Using a single enantiomer of the organocatalyst, both enantiomers of the resulting Michael adducts are obtained in high yields by simply changing the reaction solvent from aqueous DMF (up to 84 % ee) to chloroform (up to 86 % ee). Theoretical calculations are used to explain this uncommon reversal of the enantioselectivity; two transition state orientations of different polarities are differently favoured in polar or nonpolar solvents.

The authors are grateful for the financial support from the Spanish Ministerio de Economía y Competitividad (MEC) (project number CTQ2011-24151), Fondos Europeos para el Desarrollo Regional (FEDER), the COST Action CM0905 “Organocatalysis”, the FP7 Marie Curie Action of the European Commission via the ITN ECHONET Network (FP7-MCITN-2012-316379), the University of Alicante and the University of the Basque Country.