有机自由基通常是具有异常高反应性的短寿命中间体。从战略上讲,实现由有机自由基介导的合成有用的转化需要有效的引发和选择性终止事件。在这里,我们报告了一种新的催化策略,即双金属自由基氧化还原继电器,用于环氧化物向烯丙醇的区域和立体选择性重排。这种方法利用了 Ti 和 Co 配合物的丰富氧化还原化学,并将还原性环氧化物开环(引发)与氢原子转移(终止)相结合。至关重要的是,在影响关键的成键和断裂事件时,Ti 和 Co 催化剂彼此进行质子转移/电子转移以实现周转,从而构成真正协同的双催化系统。
The reaction of several stereoisomeric epoxy alcohols, obtained from R-(-)-carvone, and their corresponding formates, acetates, and benzoates, promoted by Cp2TiCl has been studied. The different outcomes of the reaction of epoxy derivatives are rationalized in terms of mechanistically biased processes. The radicals emerging from oxirane cleavage provide two types of reaction: dehydroxylation (deoxy-carbonylation) and dehydrogenation.The results offer considerable support for the radical elimination theory of hydroxyl, formyloxyl, and acetoxyl groups. The inability of tertiary radicals to be reduced by the Ti(III) complex is demonstrated unequivocally. (c) 2012 Elsevier Ltd. All rights reserved.