Ruthenium-catalyzed one-pot synthesis of primary amides from aldehydes in water

The readily available arene-ruthenium(II) complex [RuCl2(eta(6)-C6Me6){P(NMe2)(3)}] (5 mol%) proved to be an efficient catalyst for the direct synthesis of primary amides from aldehydes and hydroxylamine hydrochloride (NH2OH.HCl) in water at 100 degrees C. The process, which requires the presence of NaHCO3 to catch the HCl released during the formation of the key aldoxime intermediates, was operative with both aromatic, heteroaromatic, alpha,beta-unsaturated and aliphatic aldehydes, and tolerated several functional groups. A greener approach using commercially available NH2OH solution (50 wt.% in water) is also presented.