Oxaazabicyclooctene Oxides, Another Type of Bridgehead Nitrones: Diastereoselective Assembly from Acetylene gas, Ketones and Hydroxyl Amine.

Unique bridgehead nitrones, 8-oxa-6-azabicyclo[3.2.1]oct-6-ene 6-oxides, have been diastereoselectively assembled via acetyldihydropyrans, products of one-pot self-organization of two molecules of ketones and two molecules of acetylene, which after oximation undergo acid-catalyzed ring-closure. The proposed mechanism includes the enol double bond protonation followed by intramolecular cyclization involving the interaction of the carbocation formed with nitrogen atom. A broad range of substrates tolerates this facile transformation, in which the bridgehead nitrones were isolated in high yields.