Ru(II)-Catalyzed C–H Activation/Alkylation of 3‑Formylbenzofurans with Conjugated Olefins: Product Divergence

Ru-catalyzed alkylation of 3-formylbenzofuran
with acrylates and acrylamides has been described. Branched selectivity
with unsubstituted or β-substituted acrylates/acrylamides and
linear selectivity with α-substituted acrylates have been observed.
However, in all of the cases, the intermediate alkylation products
seem to undergo further reactions, either cycloannulation or deformylation,
depending on the substrate employed. For example, with methyl acrylate,
the intermediate branched alkylation product underwent cycloannulation
with another molecule of methyl acrylate, resulting in a densely functionalized
cyclohexene ring formation. On the other hand, in the case of N-monosubstituted
acrylamides, the branched alkylation proceeded with intramolecular
aldehyde–amide condensation, leading to pyridin-2-one ring
annulation. However, with both methacrylate and crotonate, deformylation
of the initially formed alkylation products was observed.