Ruthenium-Catalyzed Conjugate Hydrogenation of alpha,beta-Enones by in situ Generated Dihydrogen from Paraformaldehyde and Water

Notwithstanding that the highly selective hydrogenation of alpha,beta-enones to allylic alcohols can be realized by using Noyori's Ru bifunctional system, the selective reduction of the C=C bonds in alpha,beta-enones without touching the C=O bonds still lacks a general, simple, and efficient procedure. Ruthenium-catalyzed conjugate hydrogenation of various alpha,beta-enones to saturated ketones with high selectivity was investigated. The most important feature of this procedure was that hydrogen in situ generated from paraformaldehyde (or formalin) and water was employed as the reductant.