Formation of "methylene" nitrones in some nitrosoarene - olefin reactions

Abstract

On the basis of preliminary kinetic investigations, the mechanism of addition of nitrosobenzene to styrene and similar compounds was advanced as occurring by an initial 2 + 2 cycloaddition of styrene and nitrosobenzene followed by ring opening to a diradical species which reacts with additional nitrosobenzene to form isomeric 2,3,5-triphenyl-1,2,5-oxadiazolidine-N-oxides.

Unlike the reaction of styrene and nitrosobenzene, the reaction of trifluoronitrosomethane with styrene was found to undergo a multiple Diels-Alder addition to form 4,10-diaza-4,10-bis(trifluoromethyl)-3,9-dioxatricyclo[6.2.2.02,7]dodeca-6,11-diene. Although all isomeric structure for this product were not eliminated from consideration, the fact that two successive Diels-Alder cycloadditions had occurred was confirmed by thermolysis, hydrogenation, and elemental analysis. In a similar manner, 2-phenylpropene formed a multiple Diels-Alder adduct at low temperatures; at elevated temperature an "ene" product, N-(tri-fluoromethyl)-N-(2-phenyl-2-propenyl)hydroxylamine, was preferentially formed.

N-methylenephenylamine-N-oxide, N-methylene(4-methylphenyl)-amine-N-oxide, and N-methylenemethylamine-N-oxide were generated by thermolysis of the corresponding N, N'-dihydroxymethanediamines in the presence of various dipolarophiles. The resulting cycloadditions provided a convenient synthesis for some previously inaccessible isoxazolidines. The same method was used to synthesize stable N-methylene-amine-N-oxides, e.g., N-mesitylamine-N-oxide and N-methylene-tert-butylamine-N-oxide, which were previously prepared through the use of diazomethane.

The addition of nitrosobenzene to styrene and 1,1-diphenyl-ethylene has been shown to proceed through 1,2,5-oxadiazolidine-N-oxide intermediates which undergo subsequent thermal decomposition to N-methylenephenylamine-N-oxide and more highly substituted nitrones. Evidence for the presence of N-methylenephenylamine-N-oxide in reaction media was provided by isolation of its cycloadduct with N-phenylmaleimide, and as an adduct of aniline and nitrosobenzene. Similarly, N-ethylidine-phenylamine-N-oxide was isolated as a cycloadduct of N-phenylmaleimide from the reaction of nitrosobenzene with 1-(3,4-methylenedioxyphenyl)-propene.