133610-04-5Relevant articles and documents
Thermal Decomposition of 3,3,5-Trisubstituted-4,4-dimethyl-4,5-dihydro-5-hydroperoxy-3H-pyrazoles: Route to β,γ-Unsaturated Ketones
Baumstark, Alfons L.,Vasquez, Pedro C.
, p. 113 - 117 (2007/10/02)
The thermal decomposition of a series of cyclic α-azo hydroperoxides (3,3,5-R1, R2, R3-4,4-dimethyl-4,5-dihydro-5-hydroperoxy-3H-pyrazoles; 2a R1 = R2 = R3 = Ph; 2b R1= R3 = Ph, R2 = Me; 2c R1 = R3 = p-Anisyl, R2 = Me; 2d R1 = R2 = Me, R3 = Ph; 2e R1 = R3 = Me, R2 = Ph), synthesized by oxidation of the corresponding 3,4-dihydro-2H-pyrazoles, proceeded smoothly with evolution of nitrogen.The relative stability series was found to be 2a > 2c ca. 2b > 2d > 2e.For 2a, the products were 1,4,4-triphenyl-2,2-dimethylpropanone and 1,1-dimethyl-2,2-diphenylethylene.For 2b-e,m β,γ-unsaturated ketones were obtained as the major products in ca. 60percent yield from the thermolyses.The products are consistent with a free-radical mechanism involving initial homolysis of the O-O bond followed by loss of nitrogen to yield a free-radical beta to the carbonyl group.For 2a, β-scission and hydrogen-atom abstraction of the hydroperoxy proton by the β-keto radical (induced decomposition) are the major pathways leading to products.For 2b-c, abstraction of a γ-hydrogen atom of the β-keto radicals by hydroxy radical accounts for the formation of the β,γ-unsaturated compounds as the major product.
