The first immobilization of a MacMillan’s first generation organocatalyst onto dendritic support is described. A modified tyrosine-based imidazolidin-4-one was grafted to a soluble high-loading hyperbranched polyglycerol via a copper-catalyzed alkyne–azide cycloaddition (CuAAC) reaction and readily purified by dialysis. The efficiency of differently functionalized multivalent organocatalysts 4a–c was tested in the asymmetric Friedel–Crafts alkylation of N-methylpyrrole with α,β-unsaturated aldehydes. A variety of substituted enals was investigated to explore the activity of the catalytic system which was also compared with monovalent analogues. The catalyst 4b showed excellent turnover rates and no loss of activity due to immobilization, albeit moderate enantioselectivities were observed. Moreover, easy recovery by selective precipitation allowed the reuse of the catalyst for three cycles.
首次将MacMillan的第一代有机催化剂固定在树枝状载体上。一种改性的基于酪氨酸的咪唑啉-4-酮通过铜催化的炔烃-叠氮化物环加成反应(CuAAC)被嫁接到可溶的高负载超支化聚甘油上,并通过透析轻松纯化。测试了不同功能化的多价有机催化剂4a-c在N-甲基吡咯与α,β-不饱和醛的不对称Friedel–Crafts烷基化反应中的效率。研究了多种取代的烯醛,以探索催化系统的活性,并将其与单价类似物进行了比较。催化剂4b显示出优秀的转化率,并且由于固定化而未损失活性,尽管观察到适中的对映选择性。此外,通过选择性沉淀的简易回收使得催化剂可以循环使用三次。