Iodine-Catalyzed Oxidative Coupling To Construct C–O Bonds for the Synthesis of 2,3-Dihydrooxepines

The iodine-catalyzed
catalytic formal [3 + 3 + 1] cycloaddition
for the preparation of a seven-membered O-heterocyclic ring is presented,
which is an achievement of methyl and carbonyl group reactivity of
3-methyl-5-pyrazolones to forge the Csp3–O bond.
This novel protocol provides a straightforward and efficient access
to structurally diverse fused O-heterocycles through an iodine-catalyzed
iodination/Kornblum oxidation/oxidative coupling/C–O bond formation
cascade reaction. This approach demonstrates the unprecedented concurrent
realization of the unique reactivity among the methyl, methylene,
and carbonyl groups in 3-methyl-5-pyrazolones for the construction
of 2,3-dihydrooxepine rings. Moreover, a broad substrate scope displays
a graceful diversity-oriented synthetic approach.