A new synthetic route to 3-oxo-4-amino-1,2,3-oxadiazole from the diazeniumdiolation of benzyl cyanide: stable sydnone iminium N-oxides

Abstract

Treating benzylcyanide with nitric oxide in basic methanol returns 3-oxo-4-phenyl-5-amino-1,2,3-oxadiazole (a 5-iminium-sydnone N-oxide), 5, in addition to the known 2-(hydroxyimino)-2-phenylacetonitrile, 6, and the bisdiazeniumdiolate imidate salt, 7. Conditions for the separation and purification of the new 1,2,3-oxadiazole 5 are described along with its theory, structure, spectroscopy, and reactivity which demonstrate the predominance of the amino tautomer over the N-hydroxide tautomer. New derivatives of 5 include a Schiff base, from the condensation with salicylaldehyde, 8, and a dimethylamino analogue of 5, from its reaction with methyliodide and NaH. As with other related 3-oxo-1,2,3-oxadiazoles 5 has pronounced acid/base stability. Theoretical calculations demonstrate that the only other prior sydnone N-oxides prepared were misformulated as the N-hydroxide imines and are better described as 3-oxo-5-amino-derivatives of 1,2,3-oxadiazoles.