Catalyst-Free Annulation of 2‑Pyridylacetates and Ynals with Molecular Oxygen: An Access to 3‑Acylated Indolizines

A catalyst
and additive-free annulation of 2-pyridylacetates and
ynals under molecular oxygen was the first developed, affording 3-acylated
indolizines in good to excellent yields. Molecular oxygen was used
as the source of the carbonyl oxygen atom in indolizines. This approach
was compatible with a wide range of functional groups, and especially
it has been successfully extended to unsaturated double bonds and
triple bonds, which were difficult to prepare by previous methods
in a single step.