Addition of Bromine to Ketenes and Bisketenes: Electrophilic Attack at Carbonyl Carbon and Neighboring Group Participation
作者:R. S. Brown、Manfred Christl、Alan J. Lough、Jihai Ma、Eva-Maria Peters、Karl Peters、Frank Sammtleben、Henryka Slebocka-Tilk、Kuangsen Sung、Thomas T. Tidwell
DOI:10.1021/jo980684h
日期:1998.8.1
Addition of bromine to bisketene (Me(3)SiC=C=O)(2) (1) gave the fumaryl dibromide E-7, whose stereochemistry was proven by X-ray structure determination. Upon warming, E-7 rearranged to the furanone 8, and this process was faster in the more polar CD(3)CN compared to CDCl(3), consistent with an ionization pathway for the rearrangement. The bromination of 1 in CH(2)ClCH(2)Cl followed second-order kinetics
将溴添加到双烯酮中(Me(3)SiC = C = O)(2)(1)得到富马酰二溴化物E-7,其立体化学通过X射线结构测定得到证实。加热后,E-7重排至呋喃酮8,与CDCl(3)相比,极性更大的CD(3)CN中此过程更快,这与重排的电离途径一致。CH(2)ClCH(2)Cl中1的溴化反应遵循二级动力学,速率常数为(2.1 +/- 0.1)x 10(4)M(-)(1)s(-)(1) 25°C。向[Br(2)]上添加1的溴的一阶依赖性归因于分子内的亲核助剂,该分子是由第二个烯基部分在1和Br(2)的初始配合物中得到E-7形成的。从头算方法已经计算出该过程的过渡结构。相比之下,PhMe(2)SiCH = C = O 11和γ-氧杂环丁烯16通过三级动力学进行溴化,在[Br(2)]中为二级,表明在限速步骤中不存在相邻基团。双烯酮Me(2)Si(CH = C = O)(2)(13)通过混合动力学与[Br(2)]中的一阶和二阶项进行溴化。