On the Influence of a Camphor-based 1,3-Diamine Fragment in a Proline-Based Organocatalyst

摘要

Multifunctional C 1-symmetric organocatalysts were prepared incorporating a camphor- and a proline-based moiety. The new catalysts were evaluated in an asymmetric aldol reaction of acetone and aromatic aldehydes. A significant increase in the catalytic activity was found for the new proline analogue with the camphor-based 1,3-diamine unit. This new organocatalyst has one free primary amine group next to the secondary amine group of the proline unit. High yields of up to 97% with good enantioselectivities (83% ee) were obtained in the aldol reaction between various aromatic aldehydes and acetone in a shorter reaction time compared with (S)-proline. A camphor-based prolineamide analogue with a thiourea group was an efficient multifunctional organocatalyst for the aldol reaction of p-nitrobenzaldehyde and cyclohexanone with 86% yield and up to 73% ee. Moreover, matched-mismatched studies with opposite stereocenters in the camphor-based 1,3-diamine fragment revealed a significant influence of this unit on the overall performance of the new organocatalyst.