Chiral primary-tertiary diamine-br?nsted acid salt catalyzed syn-selective cross-aldol reaction of aldehydes

摘要

(Figure presented) Highly syn-selective cross-aldol reaction of aldehydes has remained a challenging subject in the field of aminocatalysis. To achieve this end, chiral primary amines have been explored and the primary-tertiary diamine-Br?nsted acid salts are found to promote the cross-aldol reactions of aldehydes with high activity and syn selectivity. Among various vicinal diamines screened, l-phenylalanine derived 2a/TfOH conjugate is identified as the optimal catalyst, showing good catalytic activity (up to 97% yield) and high syn selectivities (syn/anti up to 24:1, 87% ee). The current catalysis works selectively with small aliphatic aldehydes donors such as propionaldehyde and isobutyraldehyde, but not with aliphatic aldehydes bearing larger β-substitute (>Me). In addition, the use of 2a/TfOH conjugate has also enabled the first syn-selective cross-aldol reactions of glycoaldehyde donors.