The
NH4I-triggered formal [4 + 2] annulation of α,β-unsaturated
ketoxime acetates with N-acetyl enamides has been
developed. The current protocol employs electron-rich enamides as
C2 synthons and enables the efficient and straightforward construction
of polysubstituted pyridines in moderate to good yields based on metal-free
systems. The reaction tolerates a wide range of functional groups
and represents an alternate route toward the synthesis of pyridine
derivatives.
The copper-catalyzed
[4 + 2] annulation of α,β-unsaturated ketoxime acetates
with 1,3-dicarbonyl compounds for the synthesis of three classes of
structurally diverse pyridines has been developed. This method employs
1,3-dicarbonyl compounds as C2 synthons and enables the synthesis
of multifunctionalized pyridines with diverse electron-withdrawing
groups in moderate to good yields. The mechanistic investigation suggests
that the reactions proceed through an ionic pathway.
The
first example of divergent N-heterocycle syntheses
through a copper-catalyzed three-component reaction of α,β-unsaturated ketoximes, paraformaldehyde,
and amines has been documented. In particular, this divergent synthetic
strategy was achieved by controlling the reaction conditions to afford
the corresponding imidazoles and dihydroimidazoles in moderate to
good yields with a broad substrate scope and good functional group
compatibility.
An efficient copper-catalyzed annulation of ketoxime acetates with acetoacetanilide has been developed. This strategy provides an alternate route towards the synthesis of benzofuro- and benzothieno[2,3-c]pyridines with good functional group tolerance...
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