A synthetic protocol to access O - tert -propargylic oximes derived from tertiary propargylic alcohols was established via Nicholas reaction. Thus, BF 3·OEt 2-mediated reaction between the dicobalt hexacarbonyl complex of tert -propargylic alcohols and p -nitrobenzaldoxime followed by decomplexation with cerium(IV) ammonium nitrate afforded the corresponding O - tert -propargylic oximes in good to high yields. The obtained O - tert -propargylic oximes were effectively converted into heterocycles, such as four-membered cyclic nitrones, oxazepines, and isoxazolines, by using π-Lewis acidic catalysts.