Pyrolysis oxadiazolines

A -1,3,4-Oxadiazolin-2-imine, N-phenyl-pyrolysis, 6, 437 A -1,3,4-Oxadiazolin-5-imines IR spectra, 6, 429 A -1,3,4-Oxadiazolin-2-imines hydrolysis, 6, 438... 

Warkentin and co-workers continued studies on gas-phase pyrolysis of oxadiazoline derivatives. DFT calculations and ab initio simulations of PE spectra were used in the interpretation of the experimental results <2006CJC546>. 

Muchall et al. (98CC238) have recently investigated the gas-phase thermolysis of 2,5-dihydro-2,2-dimethoxy-2,5,5-trimethyl-l//-l,2,4-oxadiazole (75) by PE spectroscopy. Decomposition of 75 was induced by means of a continuous wave (CW) C02 laser as directed heat source at 26 W, which corresponds to a temperature of 500 50°C. When the PE spectra of acetone, tetramethoxyethene, and dimethyl oxalate were subtracted from the pyrolysis spectrum, a sim-ple spectrum remained that could be identified as that of dimethoxycarbene. Thermolysis in solution (94JA1161) had shown formation of tetramethoxyethene, and FVP experiments (92JA8751) gave dimethyl oxalate, both of which arise from the common precursor, dimethoxycarbene. Thermolysis of oxadiazolines similar to 75 in solution affords dialkoxycarbenes via an intermediate carbonyl ylide (94JOC5071). 

Oxadiazole is thermally stable and this stability is increased on substitution, particularly by aryl and perfluoroalkyl groups. Oxadiazolin-5-ones and -5-thiones are somewhat less stable and undergo selective pyrolysis at high temperatures. 

Aminoethyl)-l,2,4-oxadiazoles (606 R = alkyl or aryl) readily isomerize to 3-acylamino-2-pyrazolines (607) on heating. Treatment of the salt (608) with triethylamine yields the transient ylide (609), which decomposes to methyl-phenylcarbodi-imide (610). 2,3-Diphenyl-l,2,4-oxadiazolin-5-one (611) rearranges photochemically to a mixture of the oxadiazolinones (612) and (613) pyrolysis gives 2-phenylbenzimidazole with extrusion of carbon dioxide. The oxadiazole (614) rearranges thermally to the indazole (615). ... 

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