1.2.4- Oxadiazoline-3-carboxylic acids

The z1j-l,3,4-oxadiazoline-2-thiones which may be prepared from carboxylic acid hydrazides and carbon disulfide in basic medium are listed in Table 14-... 

The products of the reaction between carboxylic acid hydrazides and carbon disulfide cyclize very readily to Zl4-l,3,4-oxadiazoline-2-thiones (LXXXIII) (see Section II.7). The intermediates, the acyl- or benzoyl-dithiocarbazic acids may, however, also be isolated and reacted with alkyl halides to give S-alkyl dithiocarbazates (LXXXVIIIa) which also cyclize easily either to thiadiazoline or oxadiazoline rings according to the reaction circumstances (see Section II.7). 

Methylaziridine is shown to react with carbon dioxide in the presence of iodine to give 4-methyl-2-oxazolidone in 80% yield (Scheme 134). Acyl hydrazones gave 2-substituted 4-acyl-l,3,4-oxadiazolines when treated with carboxylic acid anhydrides in pyridine (Scheme 135), whereas, in a somewhat analogous reaction. 

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