Manganese-catalyzed asymmetric transfer hydrogenation of quinolines in water using ammonia borane as a hydrogen source.

The first example of manganese-catalyzed asymmetric transfer hydrogenation of N-heteroaromatics in water is reported. This ATH reaction proceeds smoothly without the need for inert atmosphere protection in the presence of a water-stable manganese catalyst, which bears an easily available aminobenzimidazole ligand. Ammonia borane, regarded as a green, cheap and high atom economical hydrogen source, was applied. Various quinolines are transformed into the desired products in high yields and up to 99% enantiomeric excess (ee). The utility of the current protocol was demonstrated by applying it in the gram-scale total synthesis of the Hancock alkaloid (−)-cuspareine with 96% overall yield. [ABSTRACT FROM AUTHOR]