Synthesis and structural characterization of l-prolinol derived chiral eutectic mixtures as sustainable solvents in asymmetric organocatalysis

Abstract

The present study focuses on the synthesis, characterization, and examination of the organocatalytic properties of a series of structurally novel L-Prolinol-based chiral solvents. Different L-Prolinol/TBAB and L-Prolinol/Glycolic acid (GA) mixtures have been characterized and evaluated for their structural characteristics using ATR-FTIR spectroscopy, differential scanning calorimetry (DSC), and NMR techniques including diffusion and NOESY NMR measurements. The structural characteristics of the L-Prolinol-based chiral solvents enabled these novel materials to display organocatalytic activities in the asymmetric conjugate addition of ketones to nitroolefins, showing the chiral liquid L-Prolinol/GA: 1/1 the highest yields and selectivities being similar or superior to those displayed by L-Prolinol in VOC or under neat conditions. Moreover, the new chiral liquid was successfully recovered and reused with minimal loss of performance over several cycles. Regarding the reaction mechanism, it has been detected a rapid formation of the oxazoline intermediate by NMR spectroscopy.