Ruthenium-catalysed asymmetric transfer hydrogenation of N-(tert-butanesulfinyl)imines

The ruthenium complex prepared from [RuCl2(p-cymene)]2 and (1S,2R)-1-amino-2-indanol is a very efficient catalyst for the asymmetric transfer hydrogenation of (R)-N-(tert-butanesulfinyl)ketimines in isopropanol. By carefully removing all possible moisture from the reaction medium, chiral primary amines with very high optical purities (up to >99% ee) can be easily prepared in excellent yields by the diastereoselective reduction of the imines followed by removal of the sulfinyl group under mild acidic conditions. Reaction times of 1–4 h were needed to complete the reduction reactions when they were performed at 40 °C.