Department Chemie and Catalysis Research Center (CRC), Technische Universität München, Lichtenbergstraße 4, 85747, Garching, Germany.
Department of Chemistry, University of Basel, St. Johanns-Ring 19, 4056, Basel, Switzerland.
Angew Chem Int Ed Engl. 2020 Jun 8;59(24):9659-9668. doi: 10.1002/anie.202001634. Epub 2020 Apr 1.
Chiral eniminium salts, prepared from α,β-unsaturated aldehydes and a chiral proline derived secondary amine, underwent, upon irradiation with visible light, a ruthenium-catalyzed (2.5 mol %) intermolecular [2+2] photocycloaddition to olefins, which after hydrolysis led to chiral cyclobutanecarbaldehydes (17 examples, 49-74 % yield), with high diastereo- and enantioselectivities. Ru(bpz) (PF ) was utilized as the ruthenium catalyst and laser flash photolysis studies show that the catalyst operates exclusively by triplet-energy transfer (sensitization). A catalytic system was devised with a chiral secondary amine co-catalyst. In the catalytic reactions, Ru(bpy) (PF ) was employed, and laser flash photolysis experiments suggest it undergoes both electron and energy transfer. However, experimental evidence supports the hypothesis that energy transfer is the only productive quenching mechanism. Control experiments using Ir(ppy) showed no catalysis for the intermolecular [2+2] photocycloaddition of an eniminium ion.
手性烯基脒盐由α,β-不饱和醛和手性脯氨酸衍生的二级胺制备，在可见光照射下，用钌催化剂（2.5 mol%）进行了分子间[2+2]光环加成反应，生成烯烃，然后水解得到手性环丁烷甲酰醛（17 个实例，49-74%收率），具有高的非对映选择性和对映选择性。Ru(bpz)(PF )被用作钌催化剂，激光闪光光解研究表明，该催化剂仅通过三重态能量转移（敏化）起作用。设计了一种带有手性仲胺共催化剂的催化体系。在催化反应中，使用了 Ru(bpy)(PF )，激光闪光光解实验表明它同时经历电子和能量转移。然而，实验证据支持能量转移是唯一的有效猝灭机制的假设。使用 Ir(ppy)的对照实验表明，烯基脒离子的分子间[2+2]光环加成没有催化作用。
