Catalytic Asymmetric Cascade Vinylogous Mukaiyama 1,6-Michael/Michael Addition of 2‑Silyloxyfurans with Azoalkenes: Direct Approach to Fused Butyrolactones

An
unprecedented cascade vinylogous Mukaiyama 1,6-MA/MA of 2-silyloxyfurans
and azoalkenes was realized with a Cu­(II)/tBu-Box complex. An array of fused butyrolactones containing multiple
stereocenters was generally obtained in good yield (up to 90% yield)
with exclusive diastereoselectivity (>20:1 dr) and excellent enantioselectivity
(up to 99% ee). Carbon isotope effects measured by 13C
NMR revealed a stepwise mechanism for this annulation process.

本研究成功实现了以铜(II)/叔丁基Box配体络合物（Cu(II)/tBu-Box complex）为催化体系的前所未有的2-硅氧基呋喃与偶氮烯烃的插烯型Mukaiyama级联1,6-迈克尔加成/环化（vinylogous Mukaiyama 1,6-MA/MA）反应。该反应可生成一系列含有多个手性中心的稠合丁内酯产物，通常能取得良好收率（最高可达90%），并展现出专一无杂的非对映选择性（>20:1 dr）与优异的对映选择性（最高达99% ee）。通过碳-13核磁共振光谱（13C NMR）测定的碳同位素效应，揭示了该环化过程的分步反应机理。