Catalytic hydrogen-mediated cross-coupling of enones and carbonyl compounds: Aldol condensation by hydrogenation

Catalytic hydrogenation of enones and enals in the presence of aldehyde and ketone partners results in the formation of aldol products. A key feature of such hydrogen-mediated C-C bond formations relates to the heterolytic activation of elemental hydrogen by cationic rhodium(i) complexes, that enables monohydride-based catalytic cycles for which direct alkyl-hydrogen reductive elimination pathways are disabled. Here, a concise over-view of catalytic hydrogen-mediated aldol condensation is presented.