2,4-Dinitrophenol as an Effective Cocatalyst: Greatly Improving theActivities and Enantioselectivities of Primary AmineOrganocatalysts for Asymmetric Aldol Reactions

摘要

Seven primary amine organocatalysts la—g were readily prepared from natural primary amino acids viatwo steps and then were used to catalyze the direct asymmetric aldol reaction, but they showed verypoor enantioselectivities and activities. As an effective cocatalyst, 2,4-dinitrophenol (DNP) dramaticallyelevated the activities and enantioselectivities of these very inefficient primary amine organocatalysts.This remedial course to the very inefficient organocatalysts by selection and employment of the optimalcocatalyst was particularly cost-effective and environment-beneficial compared with de novo developmentof catalysts. The highest efficient organocatalytic system that was composed of if and DNP showed highenantioselectivities and good to high diastereoselectivities with a broad spectrum of seven ketones. Thelinear ketones and cyclopentanone got predominant syn products whereas cyclohexanone mainly gaveanti products.