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。
Oxidation with selenium dioxide: the first report of solvent-selective steroidal aromatization, efficient access to 4β,7α-dihydroxy steroids, and syntheses of natural diaromatic ergosterols
Seleniumdioxideoxidation of cholesterol reveals a solvent-dependent product selectivity and facile one-pot synthesis of three derivatives, including aromatic analogues of naturally occurring ergosterol. Efficient access to 4β,7α-dihydroxy cholesterol is described. Analogous chemistry of β-sitosterol and diosgenin is also reported. The protocol is found effective to synthesize two diaromatic ergosterol