Asymmetric [4 + 2] Annulation Reactions Catalyzed by a Robust, Immobilized Isothiourea
作者:Shoulei Wang、Javier Izquierdo、Carles Rodríguez-Escrich、Miquel A. Pericàs
DOI:10.1021/acscatal.7b00360
日期:2017.4.7
A polystyrene-supported isothiourea (1a) behaves as a highly efficient organocatalyst in a variety of formal [4 + 2] cycloaddition reactions. The catalytic system has proven to be highly versatile, leading to six-membered heterocycles and spiro-heterocycles bearing an oxindole moiety in high yields and very high enantioselectivities (32 examples, including the previously unreported oxindole spiropyranopyrazolones
在各种形式的[4 + 2]环加成反应中,聚苯乙烯负载的异硫脲(1a)表现为高效的有机催化剂。催化系统已被证明具有高度的通用性,可以以高收率和极高的对映选择性生成带有羟吲哚部分的六元杂环和螺杂环(32个实例,包括以前未报道的羟吲哚螺并吡喃并吡喃酮8 ;平均ee为97%)。在操作条件下1a的显着化学稳定性可实现高可回收性(11个循环,累积TON为76.8),并允许实施扩展操作的连续流工艺(18小时后收率或ee不会降低)。