Metal-Carbenoid-Mediated Selective Transformation: Experimental and DFT Studies of Ag, Pd, and Rh with Enaminones and Diazoesters

Transition-metal-catalyzed transfer of a carbene group
via in situ
generated carbenoid intermediates from α-diazocarbonyls is a
powerful method for initiating diverse cascade sequences that rapidly
lead to the generation of structural complexity. Despite significant
advancements in carbenoid-enabled catalytic pathways, such as insertions
and cyclopropane formation, there has been limited exploration of
the selective control of catalytic processes involving carbenoid chemistry.
In this study, we reported a metal-carbenoid-mediated cascade transformation
approach that allows for selective control by employing different
transition metals, including silver, palladium, and rhodium, assisted
by a comprehensive density functional theory (DFT) mechanism investigation.
Through detailed mechanistic studies, we demonstrate that silver-carbenoids
and rhodium-carbenoids yield distinct tandem cyclization products,
while palladium-carbenoids afford quaternary α-imine compounds
as the final product through direct proton transfer from the same
intermediate. Furthermore, the origin of the catalyst-dependent selectivity
is elucidated through DFT calculations.