Pd 催化的苯酚烯丙基碳酸酯的不对称烯丙基烷基化 (AAA) 是构建烯丙基 CO 键的有效策略,允许获得高达 98% ee 的手性色满。详细探讨了 pH 值的影响和烯烃几何结构的影响,以及取代模式对 ee 和手性色满的绝对构型的影响。这些观察结果表明一种机制涉及反应性更强的 pi-烯丙基钯非对映体中间体的环化作为对映体区分步骤(Curtin-Hammett 条件)。这种方法导致了维生素 E 核心的对映选择性合成,首次对 (+)-clusifoliol 和 (-)-siccanin 进行了对映选择性全合成,以及合成了 (+)-红花紫杉酸 A 的高级中间体。
A new approach to fused furan ring systems and benzofurans: intramolecular cyclization reactions of unsaturated acyloxy sulfone derivatives
作者:Yuan Liu、Hollie K. Jacobs、Aravamudan S. Gopalan
DOI:10.1016/j.tetlet.2011.03.120
日期:2011.6
Unsaturated acyloxy sulfones 3 undergo intramolecular cyclization upon deprotonation with LHMDS in THF. Dehydration and double bond isomerization of the products upon exposure to acid, gave the fused ring furans, 4, in good yields. This strategy could be readily adapted to prepare substituted benzofurans 12 from the cyclization reactions of acyloxy sulfones 11 prepared from phenols. Finally, this approach
Dibenzyloydihydrobenzoxathiin 1, which resisted debenzylation with SiCl4/LiI, was effectively debenzylated with SiCl4/ LiI in the presence of a catalytic amount of BF3. The HCI salt of the bis-debenzylated product 2 was isolated in 90%, yield and 99% purity. This enhanced dealkylation activity has also been observed with other substrates. (C) 2004 Published by Elsevier Ltd.