Synthesis of highly decorated chiral 2-nitro-cyclohexane carboxylic esters through microwave-assisted organocatalyzed cascade reactions |
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Authors: | Elisabetta Massolo Maurizio BenagliaDavide Parravicini Davide BrennaRita Annunziata |
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Institution: | Dipartimento di Chimica, Università degli Studi di Milano, via Golgi 19, 20133 Milano, Italy |
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Abstract: | Starting from (E)-β-substituted-β-nitroacrylates and α,β-unsaturated ketones, a stereoselective organocatalyzed one-pot methodology allowed to synthesize highly decorated chiral 2-nitro-cyclohexane carboxylic esters. The reaction is promoted by Cinchona alkaloid-derived primary amines in the presence of an acidic co-catalyst and affords two diastereoisomers, in good yields and high enantiomeric excess (often higher than 90% ee). By replacing conventional heating with microwave irradiation, cleaner reactions in shortened times (from 48 h to 30 min) were obtained, with improved dr (80:20) and high ee (up to 94%). The application of microwave technology to this organocatalytic methodology allowed also employing C1 substituted enones, leading to cyclohexanones with four contiguous stereocenters in two isomers only, and up to 99% enantioselectivity. |
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Keywords: | Cyclohexane carboxylic esters Organocatalysis Stereoselective reactions Cinchona alkaloids Cascade reactions |
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