Reactivity of malonyl radicals. Synthesis of substituted dihydronaphthalenes by manganese(III) oxidation of diethyl .alpha.-benzylmalonate in the presence of alkynes
摘要:
Oxidation of diethyl alpha-benzylmalonate (1) by Mn(III) acetate in acetic acid at 70-degrees-C in the presence of alkynes 2a-j leads to dihydronaphthalene derivatives 3a-j in moderate to good yields. A homolytic mechanism, involving oxidation of 1 to the corresponding malonyl radical, its addition to a triple bond, and intramolecular homolytic aromatic substitution of the vinyl radical adducts, is suggested. Propargylic hydrogen abstraction and dimerization at the malonic position for less reactive alkynes are the main side reactions observed. Relative and absolute rates of addition of alpha-benzylmalonyl radicals to representative alkynes and alkenes, deduced from competitive experiments, indicate a lower reactivity toward alkynes than toward the corresponding substituted alkenes. Both SOMO-LUMO and SOMO-HOMO interactions in the transition state lower the activation energy of these homolytic additions with alkenes, but only the SOMO-HOMO interaction dominates with the examined alkynes. 2-Naphthoic acid derivatives can be efficiently obtained by oxidative decarboxylation of 3 with NaI and air.
Reactivity of malonyl radicals. Synthesis of substituted dihydronaphthalenes by manganese(III) oxidation of diethyl .alpha.-benzylmalonate in the presence of alkynes
Oxidation of diethyl alpha-benzylmalonate (1) by Mn(III) acetate in acetic acid at 70-degrees-C in the presence of alkynes 2a-j leads to dihydronaphthalene derivatives 3a-j in moderate to good yields. A homolytic mechanism, involving oxidation of 1 to the corresponding malonyl radical, its addition to a triple bond, and intramolecular homolytic aromatic substitution of the vinyl radical adducts, is suggested. Propargylic hydrogen abstraction and dimerization at the malonic position for less reactive alkynes are the main side reactions observed. Relative and absolute rates of addition of alpha-benzylmalonyl radicals to representative alkynes and alkenes, deduced from competitive experiments, indicate a lower reactivity toward alkynes than toward the corresponding substituted alkenes. Both SOMO-LUMO and SOMO-HOMO interactions in the transition state lower the activation energy of these homolytic additions with alkenes, but only the SOMO-HOMO interaction dominates with the examined alkynes. 2-Naphthoic acid derivatives can be efficiently obtained by oxidative decarboxylation of 3 with NaI and air.
Bergamini, Fabrizio; Gatti, Norberto; Santi, Roberto, Journal of Chemical Research, Miniprint, 1993, # 9, p. 2455 - 2466