Synthesis of Oxadiazolines and Other Reduced Rings

The best method of synthesizing A2-oxadiazolines is the cycloaddition of aliphatic107-109 or aromatic110 nitrile oxides to Schiff bases 

Heterocyclic rings attached to the amidoxime function have been used to synthesize A2-oxadiazolines113 as exemplified by the synthesis shown below for compound 19. 

Barrans and co-workers14,85 86 used the ubiquitous benzamidoxime (Section II, A) as a starting point for the synthesis of A2- and A3-oxa-diazolines [Eq. (29)]. By displacement of the hydrogen on N-4 in the A2-oxadiazoline (19), the anion 20 was obtained. Alkylation of this anion 

One other synthesis of a A3-oxadiazoline was obtained unintentionally. Hull and Farrand114 refluxed cyanamide and phenylhydroxyl-amine in acetone expecting to obtain the disubstituted hydroxylamine (23). Instead, the solvent acetone had condensed with the hypothetical 

Grigat and Piitter115 succeeded in synthesizing a A4-oxadiazoline by cycloaddition of a nitrone to an arylcyanate43 [Eq. (30)]. 

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