Intramolecular cyclisations of biphenyl-2-carboxyl radicals: evidence for a II-state aroyloxyl radical
作者:Stephen A. Glover、Stephen L. Golding、Andr� Goosen、Cedric W. McCleland
DOI:10.1039/p19810000842
日期:——
Biphenyl-2-carboxyl radicals generated by homolysis of acyl hypoiodites cyclise intramolecularly giving mainly δ-lactones through Ar2-6 cyclisation. 2′-Alkoxybiphenyl-2-carboxyl radicals do not give the expected Ar1-5 cyclisation product but undergo a homolytic ipso-substitution of the 2′-substituent. The phenanthrene-4-carboxyl radical gives 5H-phenanthro[4,5-bcd]pyran-5-one. Consideration of the
酰基次碘酸盐均相裂解产生的联苯-2-羧基自由基分子内环化,主要通过Ar 2 -6环化生成δ-内酯。2'-烷氧基联-2-羧基不产生预期的Ar 1个-5环化产物,但经历均裂本位的2'-取代的3'-取代。菲-4-羧基产生5 H-菲[4,5- bcd] pyran-5-one。考虑到所涉及的分子轨道表明,联苯-2-羧基处于π基态且具有较高的能量,因此比相应的酰胺基自由基具有更小的热可及性Σ态。建议容易脱羧的酰氧基具有∑基态或热可接近的激发∑态。