Automated reaction progress monitoring of heterogeneous reactions: crystallization-induced stereoselectivity in amine-catalyzed aldol reactions

A prototype automated system has been developed, which is capable of acquiring accurate kinetic reaction profiles from heterogeneous reactions. The device is capable of monitoring the composition and concentration of either the dissolved components (solution phase) or slurry (solid and solution phases) in parallel. This prototype was used to study the diastereo- and enantioselectivity of the aldol reaction between 4-tert-butyl cyclohexanone and p-nitrobenzaldehyde, catalyzed by either pyrrolidine or L-proline. With both catalysts, the observed high diastereoselectivity involves an interplay between solution phase reaction/epimerization and crystallization. These observations were possible due to the facile method of tandem solution and slurry analysis.