Bicyclic β-Lactones via Intramolecular NCAL Reactions with Cinchona Alkaloids: Effect of the C9-Substituent on Enantioselectivity and Catalyst Conformation
作者:Guillermo S. Cortez、Seong Ho Oh、Daniel Romo
DOI:10.1055/s-2001-16746
日期:——
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.
C9-酰化金鸡纳生物碱可促进分子内亲核催化醛内酯化(NCAL)反应,从而生成具有光学活性的双环δ-内酯。本文提出了这一催化不对称过程的机理方案。在奎尼丁 C9 位置的各种酯、氨基甲酸酯和碳酸酯中,只观察到对映体选择性的微小变化。结合耦合常数(3 J H8、H9)和 nOe 数据,我们为这些衍生物确定了主要的溶液构象。有趣的是,一种硬度更高的奎尼丁衍生物在对映体选择的意义上出现了完全逆转。