C9-Acylated cinchona alkaloids promote an intramolecular, nucleophile-catalyzed aldol-lactonization (NCAL) reaction leading to optically active bicyclic β-lactones. A mechanistic scheme is proposed for this catalytic, asymmetric process. Only small variations in enantioselectivity were observed for a variety of esters, a carbamate, and a carbonate at the C9 position of quinidine. A combination of coupling constants (3 J H8,H9) and nOe data was used to assign predominant solution conformations for these derivatives. Interestingly, a more rigid quinidine derivative gave a complete reversal in the sense of enantioselection.
No takes yet. Share an insight, caveat, or question.
Cortez et al. (2001) studied this question.