We had reported that under thermolysis 2-benzoyl-2-halo-2H-azirine-3-carboxylates 1 undergo
ring expansion giving products in high yield which were identified
as being 4-haloisoxazoles 3 (Scheme 1).
The same products can also be obtained in high yield from the thermolysis
of haloazidoalkenes 2 via intermediate
2-benzoyl-2-halo-2H-azirines 1.
Scheme 1
Recently, new data have been disclosed allowing to demonstrate
that methyl 2-benzoyl-2-halo-2H-azirine-3-carboxylates
undergo thermal ring expansion to give 4-halo-5-phenyl-1,3-oxazole-2-carboxylates 4 and not the isomeric isoxazoles (Scheme
2).1 These 1,3-oxazoles can also be obtained in high yield from
haloazidoalkenes 2.
Scheme 2
Reference
(1) Lopes, S.; Nunes, C. M.; Fausto, R.; Pinho e Melo, T. M.
V. D. J. Mol. Struct. 2009, 919, 47.
