NHC‐Organocatalysed Hydroacylation of Unactivated or Weakly Activated C−C Multiple Bonds and Ketones

Abstract N‐Heterocyclic Carbenes (NHCs) are versatile organocatalysts owing to their umpolung capability – i. e. the catalytic transformation of electrophilic aldehydes into nucleophilic species. Profoundly, aldehyde umpolungs were exploited in Benzoin and Stetter reactions, whereas hydroacylation of unactivated carbon‐carbon multiple bonds (alkenes and alkynes) are challenging and highly desired. Normally, catalytic hydroacylation of alkenes was achieved by transition metal catalysts based on rhodium, cobalt, nickel, ruthenium, and iridium. However, the metal‐catalyzed strategy is accompanied by undesired side reactions, such as decarbonylation of aldehydes, and thus demands installation of directing group in the aldehydes. In contrast, NHCs overcome these downsides and utilize the umpolung strategy beyond the Benzoin and Stetter reactions to implement catalytic hydroacylation of unpolarised and unactivated carbon‐carbon multiple bonds (alkenes and alkynes) under mild reaction conditions with step‐ and atom‐economy. In addition, this unconventional transformation is extended to catalytic asymmetric catalysis. This highlight covers the progress and practicality of NHC‐catalyzed hydroacylation of alkenes, alkynes, arynes, and ketones to access biologically relevant organics. Both inter‐and intramolecular hydroacylation reactions in combination with Stetter were presented and key mechanistic pathways were discussed.