Labeling studies establish the following regiochemistry:
:RCDO  +  CH=CHR   →   RC(O)CHCHDR
In terms of the reaction mechanism, hydroacylation begins with oxidative addition of the aldehydic carbon-hydrogen bond. The resulting acyl hydride complex next binds the alkene. The sequence of oxidative addition and alkene coordination is often unclear. Via migratory insertion, the alkene inserts into either the metal-acyl or the metal-hydride bonds. In the final step, the resulting alkyl-acyl or beta-ketoalkyl-hydride complex undergoes reductive elimination. A competing side-reaction is decarbonylation of the aldehyde. This process also proceeds via the intermediacy of the acyl metal hydride:
:R"C(O)-ML-H   →   R"-M(CO)L-H
This step can be followed by reductive elimination of the alkane:
:R"-M(CO)L-H   →   R"-H  +  M(CO)L