Stereochemical control–-nitrones from oximes by 1,3-azaprotio cyclotransfer or 1,2-prototropy
作者:Colm O'Mahony、Frances Heaney
DOI:10.1039/cc9960000167
日期:——
Oximes 1a,b and 10 are configurationally stable at elevated temperatures, the (E)-oximes react exclusively via a concerted 1,3-azaprotio cyclotransfer reaction to give 6- and 7-membered cyclic dipoles, respectively, whilst their Z-isomers react via a 1,2-prototropy-cycloaddition sequence furnishing fused isoxazolidines.
Efficient, microwave-assisted intramolecular 1,3-dipolar cycloadditions of oximes and <i>N</i>-methylnitrones derived from <i>o</i>-alkenylmethoxy-acetophenones
stereoselective intramolecular 1,3-dipolar cycloadditions, both on microwave heating under solvent free conditions and refluxing in toluene, to afford novel cycloadducts (5a, 5b); the oxazepine-N-oxide (3a) reported to be formed in 98% yield was obtained only as a minor product (~10%). However, o-cinnamyloxy-acetophenone-oxime (2c) under similar conditions undergoes intramolecular N-alkylation to afford