A Comparison of 4-Oxazoline and 2-Acylaziridine Routes to Azomethine Ylides

Article abstract of DOI:10.1021/jo00244a009

Pyrolysis of aziridines 6 or 7 affords azomethine ylides, which can also be generated from 3-methyl-2,5-diphenyl-4-oxazoline (1a) at room temperature.Attempts to trap the thermally generated ylide with dimethyl acetylenedicarboxylate afford increasing amounts of the unusual enamine product 9 as the temperature decreases.The aziridine-derived dipoles (2a or 3a vs 4a or 5a) cannot be trapped prior to equilibration.Similar results are obtained from the aziridines 16/17, but in this case, dipole isomers can be intercepted by N-phenylmaleimide in xylene solution.The 2,3-dimethyl-5-methoxy-4-oxazoline derived dipole 2b probably does not equilibrate, but its 2 + 3 cycloadducts correspond to the major products formed by aziridine pyrolysis under equilibrating conditions.