Alkyl radical generation using cyclohexa-1,4-diene-3-carboxylates and 2,5-dihydrofuran-2-carboxylates
作者:Gavin Binmore、Liberato Cardellini、John C. Walton
DOI:10.1039/a606414k
日期:——
3-Methylcyclohexa-1,4-diene-3-carboxylic acid and
2-methyl-2,5-dihydrofuran-2-carboxylic acid were prepared by Birch
reduction and alkylation of benzoic and furoic acid respectively and
converted to alkyl esters. Cyclohexadienyl and 2,5-dihydrofuranyl
radicals were generated by hydrogen abstraction and characterised by EPR
spectroscopy. The esters decomposed thermally in the presence of a
radical initiator to generate alkyl radicals which could be trapped with
moderate efficiency by halogen donors or alkenes. Loss of methyl to
afford an alkyl benzoate was an important side reaction at higher
temperatures. From the thermal reaction of hex-5-enyl
3-methylcyclohexa-1,4-diene-3-carboxylate the rate constant for hydrogen
abstraction from the ester by hexenyl radicals was determined to be
0.82 × 105 dm3
mol-1 s-1 at 140 °C.
3-甲基环己-1,4-二烯-3-羧酸和2-甲基-2,5-二氢呋喃-2-羧酸通过Birch还原和分别对苯甲酸和糠酸的烷基化制备而成,并转化为烷基酯。环己二烯基和2,5-二氢呋喃基自由基通过氢抽提生成,并利用电子顺磁共振(EPR)光谱进行表征。在自由基引发剂存在下,酯类通过热分解生成烷基自由基,这些自由基可以被卤素供体或烯烃以中等效率捕获。在较高温度下,甲基的丢失以形成烷基苯甲酸酯是一个重要的副反应。从己-5-烯基3-甲基环己-1,4-二烯-3-羧酸酯的热反应中,测定了己烯自由基从酯中抽提氢的速率常数为0.82 × 105 dm3 mol-1 s-1,温度为140°C。