Synthetic routes to pure 1-phenylcyclohexa-2,5-diene-1-carboxylic acid and derived esters were developed. Esters containing appropriately unsaturated side chains generated the corresponding alkenyl radicals and hence gave good yields of 5-exo ring closure products in organotin-free reactions. Extrusion of phenyl radicals from the intermediate cyclohexadienyl type radicals was not observed, and this alternative β-scission did not compete under any conditions. Yields from alkylations of olefins in analogous intermolecular processes were, however, poor. As a spin-off from the research, it was found that 1-phenylcyclohexa-2,5-diene-1-carboxylic acid (6) was a useful source of hydroxyformyl (formate) radicals in organic solvents.
开发了纯
1-苯基环己-2,5-二烯-1-羧酸及其衍生酯的合成路线。含有适当不饱和侧链的
酯类可生成相应的烯基自由基,因此在无
有机锡反应中,5-外环闭合产物的产量很高。没有观察到苯基自由基从中间的环
己二烯型自由基中挤出,而且这种替代性的 β 分裂在任何条件下都不会产生竞争。不过,在类似的分子间过程中,烯烃烷基化的产量很低。研究的一个附带成果是发现
1-苯基环己-2,5-二烯-1-羧酸(6)是有机溶剂中羟基甲酰(
甲酸)自由基的有效来源。