FREE-RADICAL CYANATION - NOVEL FREE-RADICAL REACTION OF METHYL CYANOFORMATE OR CYANOGEN WITH 2,4-DIMETHYLPENTANE

The peroxide-initiated free-radical chain cyanation of several hydrocarbons with methyl cyanoformate has been observed. The reaction is proposed to proceed through the intermediacy of an iminyl radical formed from the addition of an alkyl radical to the carbon-nitrogen triple bond. The resulting iminyl radical undergoes β-scission to form the alkyl cyanide (>70%), carbon dioxide, and a methyl radical which subsequently carries the chain. Only traces of products possibly arising from carbonyl addition were observed. The peroxide promoted reaction of the reagent with 2, 4-dimethylpentane yielded only minor amounts of the three possible cyanides (20%), but gave as the major product in 55% yield the difunctionalized cyclic hydrocarbon, 2-carbomethoxy-3.3, 5, 5-tetramethylazacyclopent-l-ene. The reaction pathway for the formation of the cyclized product proceeds by addition of the first formed tertiary alkyl radical to the cyano triple bond to form the iminyl radical, the same radical used to rationalize the chain cyanation; internal hydrogen abstraction by the iminyl radical formed from this addition (six-membered ring transition state), followed by addition of the new tertiary radical to the nitrogen of the imine double bond (five-membered ring transition state) and disproportionation of the new radical to yield the difunctionalized cyclic product in a nonchain process. Consistent with this mechanism was the observation that a modest yield (22%) of difunctionalized cyclic product, 2-cyano-3, 3, 5, 5-tetramethylazacyclopent-l-ene, was formed by the nonchain reaction of cyanogen with 2, 4-dimethylpentane. © 1979, American Chemical Society. All rights reserved.