Organocatalytic conjugate addition reactions
We have found a route that uses direct Michael reaction to synthesize various butenolide structures. Its feasibility is displayed from its tolerance to a wide range of different substituted alpha, beta-unsaturated lactones and maleimides. Chiral sulphonamide catalyst proved to be an efficient catalyst for base catalyzed conjugate addition between 2(3H)-furanones and maleimides. Aromatic furanones substrates proved to be better than alkyl furanones, giving higher yields and better ees. The best result is a decent ee of 70%. There is still room for improvements in increasing both the yield and the ee of the butenolide products. We have also developed an enantioselective Oxo-Michael reaction catalyzed by another base chiral bicyclic guanidine between hydroxycarbamates and maleimides. The feasibility of the reaction was shown by the high yields that were generally achieved although only modest enantioselectivities (of up to 60% ee) were obtained. Further improvements are still possible.
Organocatalytic, Michael, Guanidine, sulphonamide, Oxo-Michael, enantioselective
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