Competitive 1,2-C Atom Shifts in the Strained Carbene Spiro[3.3]hept-1-ylidene Explained by Distinct Ring-Puckered Conformers
作者:Murray G. Rosenberg、Theodor Schrievers、Udo H. Brinker
DOI:10.1021/acs.joc.6b02445
日期:2016.12.16
Spiro[3.3]hept-1-ylidene is a markedly strained carbene reaction intermediate that was generated by high-vacuum flash pyrolysis (HVFP) of the corresponding p-tosylhydrazone sodium salt. Five hydrocarbons were produced from the Bamford–Stevens reactant in 82% overall yield. The carbene undergoes two [1,2]-sigmatropic rearrangements via competing 1,2-C atom shifts. Ring-contraction yields cyclopropylidenecyclobutane
螺[3.3]庚-1-亚基是一种显着拉紧的卡宾反应中间体,由相应的对甲苯磺酰hydr钠盐的高真空闪速热解(HVFP)产生。班福德-史蒂文斯反应物生产了五种烃,总产率为82%。卡宾通过竞争性的1,2-C原子位移经历了两个[1,2]-σ重排。环收缩产生环亚丙基环丁烷,而环扩展产生双环[3.2.0]庚-1(5)-烯。尽管形成了一些1-亚甲基螺[2.3]己烷,但是环的收缩是区域特异性的。它不在HVFP条件下源自卡宾。相反,它来自化学活化的环亚丙基环丁烷的亚甲基环丙烷型重排。类似地,一些化学活化的双环[3.2.0]庚-1(5)-烯经由环的开环重排为1,2-二亚甲基环戊烷。考虑到初级产物向次级产物的转化,相对产率表明,卡宾内的环收缩比环扩展占优势6.7:1。计算化学被用来评估这些重排的结构,构象,能量,应变能,过渡态和活化能,目的是解释产物的选择性。预计双环卡宾将采用与过渡态选择有关的四个不同的几何构象