Herein, previously unreported Fischer's base reactants serving as useful 2C building blocks in (3+2) cycloaddition reactions to build a library of bispiro[Fischer's base-oxindole] hybrids are described. These structurally intriguing products containing three adjacent quaternary stereocentres were smoothly afforded in up to 82% yield and >20 : 1 dr under catalyst-free conditions. Notably, the present protocol firstly employs 3-isothiocyanato oxindole serving as an acceptor and then as a donor in the formal (3+2) cycloadditions, allowing practical, straightforward access to structurally diverse cycloadducts. This work expands the applicability scope of 3-isothiocyanato oxindoles, which have been limited to behaving as donor/acceptor-based synthons in cycloadditions in previous work.

中文翻译：

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Fischer 碱基触发的正式 (3+2) 环加成与 3-isothiocyanato oxindoles 作为受体-供体合成子

在此，描述了以前未报道的 Fischer 碱反应物作为 (3 + 2) 环加成反应中有用的 2C 构建单元，以构建双螺旋 [Fischer 碱-羟吲哚] 杂化物库。这些结构有趣的产品包含三个相邻的季立体中心，在无催化剂条件下以高达 82% 的收率和 >20:1 dr 顺利提供。值得注意的是，本协议首先使用 3-isothiocyanato oxindole 作为受体，然后在正式的 (3+2) 环加成中作为供体，允许实际、直接地访问结构多样的环加合物。这项工作扩大了 3-isothiocyanato oxindoles 的适用范围，在以前的工作中，它仅限于在环加成中充当基于供体/受体的合成子。