Department of Fine Chemistry, Seoul National University of Science & Technology, Seoul 139-743, Korea.
J Org Chem. 2012 Sep 7;77(17):7307-12. doi: 10.1021/jo3009963. Epub 2012 Aug 22.
A simple catalytic system that uses commercially available cobalt(II) perchlorate as the catalyst and 3-chloroperoxybenzoic acid as the oxidant was found to be very effective in the epoxidation of a variety of olefins with high product selectivity under mild experimental conditions. More challenging targets such as terminal aliphatic olefins were also efficiently and selectively oxidized to the corresponding epoxides. This catalytic system features a nearly nonradical-type and highly stereospecific epoxidation of aliphatic olefin, fast conversion, and high yields. Olefin epoxidation by this catalytic system is proposed to involve a new reactive Co(II)-OOC(O)R species, based on evidence from H(2)(18)O-exchange experiments, the use of peroxyphenylacetic acid as a mechanistic probe, reactivity and Hammett studies, EPR, and ESI-mass spectrometric investigation. However, the O-O bond of a Co(II)-acylperoxo intermediate (Co(II)-OOC(O)R) was found to be cleaved both heterolytically and homolytically if there is no substrate.
一个简单的催化体系，使用商业可得的高氯酸钴（II）作为催化剂和 3-氯过氧苯甲酸作为氧化剂，在温和的实验条件下，对于各种烯烃的环氧化反应非常有效，具有高产物选择性。更具挑战性的目标，如末端脂肪族烯烃，也可以有效地和选择性地氧化为相应的环氧化物。该催化体系具有近乎非自由基型和高度立体选择性的脂肪族烯烃环氧化、快速转化和高收率的特点。基于 H(2)(18)O 交换实验、过氧苯乙酸作为机理探针的使用、反应性和哈米特研究、EPR 和 ESI-质谱研究的证据，提出了烯烃环氧化由新型反应性 Co(II)-OOC(O)R 物种催化，但是，如果没有底物，Co(II)-酰基过氧中间体（Co(II)-OOC(O)R）的 O-O 键既可以异裂又可以均裂。
