Catalyst-Directed Divergent Catalytic Approaches to Expand Structural and Functional Scaffold Diversity via Metallo-Enolcarbene Intermediates

Catalyst-directed access to divergent
products involving three
different metals that exclusively form three different products from
the same reactants is reported. Each catalyst directs an individual
metallo-enolcarbene pathway from enoldiazoacetates and alkenes to
a specific product. These include highly selective intermolecular
cyclopropanation catalyzed exclusively by dirhodium­(II) carboxylates,
providing spiro-substituted dihydrooxazoles with greater than 20:1
diastereoselectivity and up to 99% ee; vinylogous
addition with subsequent 1,6-proton transfer occurring independently
with either Au­(I) or Cu­(I) catalysis or [3 + 2]-cycloaddition with
a Cu­(II) catalyst; and direct cycloaddition with the CN bond
of methylenedihydrooxazoles followed by rearrangement forming multiply
substituted pyrroles in the presence of a silver catalyst. Allylic
aromatization via vinylogous addition selectively delivers aromatic
oxazole derivatives from methylenedihydrooxazoles, and when aromatization
does not occur by 1,6-proton transfer, [3 + 2]-cycloaddition is the
outcome. This catalyst-dependent formation of metallo-enolcarbene
intermediates with alkenes demonstrates the tremendous potential of
this approach to diversity-oriented-synthesis.