Chiral Aminocarbamates Derived from trans-Cyclohexane-1,2-Diamines as Organocatalysts in Conjugate Addition Reactions

Abstract

The thesis has been divided in two chapters: Chapter I describes the preparation of primary-amine monocarbamates from enantiopure trans-cyclohexane-1,2-diamines and their use as chiral organocatalysts in the enantioselective Michael addition reaction of aldehydes and ketones to maleimides, to synthesize enantiomerically enriched substituted succinimides. In the conjugate addition reaction of aldehydes to maleimides in conventional volatile organic solvents, it has been found that these organocatalysts are able to generate both enantiomers of the corresponding succinimide using only one enantiomeric form of the catalyst, just by changing the polarity of the solvent. Theoretical calculations justify the mechanism through which this inversion of enantioinduction occurred. In addition, these organocatalysts were used in the enantioselective Michael addition reaction of aldehydes to maleimides, using Deep Eutectic Solvents (DES) as recyclable and environmentally sustainable reaction medium, yielding the corresponding succinimides with excellent yields and high enantioselectivities (up to 94%). The succinimides can be extracted from the DES, which retains the chiral organocatalyst, allowing to reuse both solvent and catalyst. Moreover, the conjugate addition of ketones to maleimides using conventional solvents, allows obtaining the corresponding succinimides with excellent yields but with moderate enantioselectivities (up to 66%). Chapter II shows the results obtained in the enantioselective Michael addition reaction of aldehydes and ketones to nitroalkenes, using the former trans-cyclohexane-1,2-diamine-derived aminocarbamates as chiral organocatalysts, obtaining enantioenriched γ-nitrocarbonyl compounds. In the conjugate addition of isobutyraldehyde to nitroalkenes, the corresponding γ-nitroaldehydes were obtained with enantioselectivities up to 84%. In addition, the enantioselective conjugate addition reaction of ketones to nitroalkenes allowed to obtain interesting γ-nitroketones with high enantioselectivities (up to 96%). Theoretical calculations justify the mechanism involved during this enantioselective process.