THERMAL AND INDUCED DECOMPOSITIONS OF N-ALKOXYCARBONYLDIHYDROPYRIDINES - END-PRODUCT ANALYSIS AND EPR-SPECTRA OF AZACYCLOHEXADIENYL RADICALS

Hydrogen abstraction from N-alkoxycarbonyldihydropyridines generated a zacyclohexadienyl radicals (pyridinyl radicals) which are characterise d by EPR spectroscopy. In the presence of peroxide initiators, N-aIkox ycarbonyl-1,2-dihydropyridines decomposed with production of pyridine, the corresponding alkyl formate, alkyl benzoate and alkanol being for med as the major products. Absence of cyclised products in experiments with substrates containing hex-5-enyl, pent-4-enyloxy etc. units demo nstrates that radical production must be minor and that N-alkoxycarbon ylazacyclohexadienyl radicals do not readily undergo beta-scission of the exocyclic N-C bond. The most probable mechanism is a direct 1,2-el imination of formate, The alcohols which accompanied the other product s are probably formed by hydrolysis of the formates and benzoates, Ana logous chemistry is displayed by N-alkoxycarbonyI-1,4-dihydropyridines at higher temperatures where 1,4-elimination of formate is too rapid for homolytic radical production to compete.