Rapid and selective spiro-cyclisations of O-centred radicals onto aromatic acceptors
作者:Roy T. McBurney、Annika Eisenschmidt、Alexandra M. Z. Slawin、John C. Walton
DOI:10.1039/c3sc50500f
日期:——
spectroscopy showed they ring closed exclusively by spiro-cyclisation onto the ipso-C-atoms of the aromatic rings. β-Scission of the alkoxycarbonyloxyls to CO2 and benzyloxyl radicals increasingly competed and became dominant above 270 K. The first rate parameters for spiro-cyclisations of O-centred radicals onto aromatics were obtained by the steady-state kinetic EPR method. Pentafluoro-substitution of the ring
通过苄基肟碳酸酯的敏化光解产生取代的苄氧基羰基氧基。EPR光谱表明它们响仅通过关闭螺-cyclisation到本位芳环的-C-原子。在270 K以上,烷氧基羰基氧基与CO 2和苄氧基自由基的β断裂竞争越来越激烈,并逐渐占主导地位。通过稳态动力学EPR方法获得O中心自由基向芳族化合物的螺环化的第一速率参数。环的五氟取代大大降低了螺环化率。螺旋的激活壁垒DFT计算得出的环化数约为替代邻环化数的一半。对TS结构的考虑表明,螺环封闭期间,氧SOMO与芳族π系统更好的重叠导致螺环取代邻环化。