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)。