Catalytic Hydroacylation of Alkynes with Aldehydes by a Cp'Mo Catalyst.

Abstract

Transition-metal-catalyzed intermolecular hydroacylation of alkynes offers an atom-economical route to synthetically valuable enones, yet its widespread utility is often hampered by noble-metal reliance and competing decarbonylation side pathways. Herein, we report the first catalytic intermolecular hydroacylation of alkynes using non-noble molybdenum catalysts bearing a tetramethylcyclopentadienyl ligand. Under this molybdenum catalysis, the enone products were obtained in up to 97% yield with excellent E/Z selectivity. The methodology tolerates broad functional groups across aromatic, heteroaromatic, and unchelated aliphatic aldehydes alongside aryl, heterocyclic, and alkyl substituted alkynes and enables derivatization of pharmaceutically relevant molecular skeletons. The intramolecular substrate 4 exhibits catalyst-controlled divergent reactivity: the Cp'Mo complex promotes a hydroacylation process, while a Mo(CO)6/ortho-benzoquinone catalytic system switches reactivity toward carbonyl-alkyne metathesis. Preliminary mechanistic studies suggest a catalytic cycle proceeding via oxidative addition of the formyl C-H bond, alkyne migratory insertion, and reductive elimination. This work establishes low-valent Cp'Mo complexes as a distinct class of non-noble hydroacylation catalysts with unique selectivity and tunable reaction manifolds.