Electrooxidative cyclization of N-acylhydrazones of aldehydes and ketones to .DELTA.3-1,3,4-oxadiazolines and 1,3,4-oxadiazoles
作者:Toshiro Chiba、Mitsuhiro Okimoto
DOI:10.1021/jo00031a014
日期:1992.2
The electrolytic oxidation of ketone N-acylhydrazones (1) in methanolic sodium acetate induced their intramolecular cyclization to the corresponding 2-methoxy-DELTA(3)-1,3,4-oxadiazolines 3. The thermal stability of a given oxadiazoline and what products were formed by its thermal decomposition was found to depend on the natures of the substituents at C-2. Thus, 2-methoxy-2-phenyloxadiazolines preferentially yielded oxiranes 5, whereas 2-alkyl-2-methoxyoxadiazolines preferentially gave enol ethers 6. 2,2-Dimethoxyoxadiazolines decomposed to the parent ketones and many unidentified products. The electrolytic oxidation of aldehyde N-acylhydrazones 2 gave 2,5-disubstituted 1,3,4-oxadiazoles 4. The oxidative cyclization of the N-benzoylhydrazones of aliphatic aldehydes gave especially high yields of the corresponding heterocycles.