Green chemistry approach for stereoselective aldol condensation catalyzed by amino acids under microflow conditions

Abstract

Over the recent years, the pharmaceutical field has been under significant pressure to adapt to the principles of green chemistry. The industry is facing the challenge of environmental protection and securing people's health while sustaining its fundamental goals of efficiency and selectivity optimization. In this work, the reaction processes optimization has been acheived through the microfluidic approach to the widely used aldol condensation reaction. In accordance with the green chemistry principles, we have found that the best conditions include aqueous ethanol solvent and easily available amino acids used as catalysts. Asymmetric aldol condensation of para-nitrobenzaldehyde with cyclohexanone catalyzed by L-tert-Leu under microfluidic conditions provided the product with high yield and diastereoselectivity (anti/syn = 28:1) and 98% enantiomeric excess. The microfluidic reactor process, compared to the classical batch method (in a flask), provides comparable product yield, while the reaction time was reduced by an order of magnitude. It should be noted that this approach allows to carry out the reactions at low (below zero) temperatures with greater enantioselectivity.