Samarium Iodide-Catalyzed Pinacol Coupling of Carbonyl Compounds

摘要

One of the most remarkable developments hi recent organic synthesis is the application of divalent samarium compounds as excellent reducing agents. Since the pioneering works by Kagan and Inanaga in the chemistry of samarium(II) iodide (SmI_2), a widevariety of novel types of election transfer reactions which are far superior to the traditional ones in both efficiency and selectivity have been reported. Unfortunately, almost all of the electron transfer reactions required more than a stoichiornetricamount of samarium complexes, except for few examples of hydride transfer reductions such as the Meerwein-Ponndorf- Verley (MPV) reduction and the Tishchenko reaction. This is simply because a catalytic cycle of them has not been established. This limitation strongly decreases the synthetic value of the reactions promoted by low-valent samarium complexes. In this work, we report our preliminary investigation of the establishment of a catalytic cycle of SmI_2 for the reduction of catbonyl compounds.