Bicyclic β-Lactones via Intramolecular NCAL Reactions with Cinchona Alkaloids: Effect of the C9-Substituent on Enantioselectivity and Catalyst Conformation
摘要:
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。
Asymmetric Synthesis of Bicyclic β-Lactones via the Intramolecular, Nucleophile-Catalyzed Aldol Lactonization: Improved Efficiency and Expanded Scope
作者:Seong Ho Oh、Guillermo S. Cortez、Daniel Romo
DOI:10.1021/jo050024u
日期:2005.4.1
The intramolecular, nucleophile-catalyzed, aldol lactonization (NCAL) process merges catalytic, asymmetric carbocycle synthesis with β-lactone synthesis. The application of modified Mukaiyama reagents to this process led to greatly improved conversion and efficiency (70−82% yield) and shorter reaction times with no diminution of enantioselectivity (91−98% ee). The process was extended to several new
Double Diastereoselective, Nucleophile-Catalyzed Aldol Lactonizations (NCAL) Leading to β-Lactone Fused Carbocycles and Extensions to β-Lactone Fused Tetrahydrofurans
作者:Kay A. Morris、Kevin M. Arendt、Seong Ho Oh、Daniel Romo
DOI:10.1021/ol101388h
日期:2010.9.3
A double diastereoselective variant of the nucleophile-catalyzed aldol lactonization (NCAL) process is described. This strategy delivers beta-lactone-fused carbocycles with good to excellent diastereoselectivities using cinchona alkaloid catalysts with enantioenriched aldehyde acids, which gave low diastereoselectivity based on substrate control alone. beta-Lactone-fused tetrahydrofurans are also prepared for the first time via the NCAL process; however, diastereoselectivity was only modestly improved when applying double diastereodifferentiation to these systems.