Simple proline derivatives as recoverable catalysts for the large-scale stoichiometric aldol reactions

Abstract

Simple, inexpensive, highly active, recoverable and reusable proline-based organocatalysts have been developed to promote direct stoichiometric aldol reactions with excellent enantioselectivities. The proline-based organocatalyst 1c is highly efficient for the stoichiometric aldol reactions of a wide range of aromatic aldehydes with cyclic ketones, and the resulting aldol products could be obtained with up to 99 ∶ 1 anti/syn ratio and >99% ee. The proline-based organocatalyst 1c can be easily recovered and reused, and only a slight decrease in enantioselectivities was observed after seven cycles. The proline-based organocatalyst 1c can be efficiently applied to large-scale reactions with the enantioselectivities being maintained at the same level, which demonstrates potential application in industry.