Covalent immobilization of chiral dienes in mesoporous solids for asymmetric heterogeneous catalysis is highly attractive. In order to study confinement effects in bimolecular vs monomolecular reactions, a series of pseudo-C2-symmetrical tetrahydropentalenes was synthesized and immobilized via click reaction on different mesoporous solids (silica, carbon, covalent organic frameworks) and compared with homogeneous conditions. Two types of Rh-catalyzed reactions were studied: (a) bimolecular nucleophilic 1,2-additions of phenylboroxine to N-tosylimine and (b) monomolecular isomerization of isoxazole to 2H-azirne. Polar support materials performed better than non-polar ones. Under confinement, bimolecular reactions showed decreased yields, whereas yields in monomolecular reactions were only little affected. Regarding enantioselectivity the opposite trend was observed, i.e. effective enantiocontrol for bimolecular reactions but only little control for monomolecular reactions was found.

中文翻译：

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限制下不对称铑二烯催化：介孔固体中的异恶唑环收缩


将手性二烯共价固定在介孔固体中用于不对称多相催化非常有吸引力。为了研究双分子与单分子反应中的限制效应，合成了一系列假C2对称四氢戊二烯，并通过点击反应固定在不同的介孔固体（二氧化硅、碳、共价有机骨架）上，并与均相条件进行比较。研究了两种类型的 Rh 催化反应：(a) 苯基环硼氧烷与 N-甲苯磺酰亚胺的双分子亲核 1,2-加成反应和 (b) 异恶唑单分子异构化为 2H-氮丙啶。极性支撑材料的性能优于非极性支撑材料。在限制下，双分子反应的产率下降，而单分子反应的产率几乎没有受到影响。关于对映选择性，观察到相反的趋势，即对双分子反应有效的对映控制，但对单分子反应仅发现很少的控制。