Abstract
An attractive, novel, convenient process for the preparation of 3,5-disubstituted-3H -[1,3,4]-oxadiazol-2-ones and -thiones from the reaction of various equivalent and non-equivalent N -tert -butyldiacylhydrazines with potassium tert -butoxide followed by treatment with phosgene or thiophosgene, respectively, has been discovered. The 3,5-disubstituted-3H -[1,3,4]-oxadiazol-2-ones and -thiones are confirmed both analytically and chemically. Various equivalent and non-equivalent N -tert -butyldiacylhydrazines are conveniently synthesized from the reaction of tert -butylhydrazine hydrochloride in the presence of i -Pr2 NEt, with acid chloride #1 followed by subsequent treatment with acid chloride #2. Both the syntheses of 3,5-disubstituted-3H -[1,3,4]-oxadiazol-2-ones and -thiones, as well as N -tert -butyldiacylhydrazines, are easily performed on multigram scales.
Key words
cyclization - heterocycles - regioselectivity - hydrazine - phosgene
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[2 2 7 with 4-ethylbenzoyl chloride afforded 5-(3,5-dimethylphenyl)-3-(4-ethylbenozyl)-3H -[1,3,4]-oxadiazol-2-one (4a ), which was identical in all respects to 4a synthesized via our phosgene/N -tert -butyldiacylhydrazine route.
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