Diverging Effects of Steric Congestion on the Reaction of Tributylstannyl Radicals with Areneselenols and Aryl Bromides and Their Mechanistic Implications
作者:David Crich、Jae-Taeg Hwang、Stéphane Gastaldi、Francesco Recupero、Donald J. Wink
DOI:10.1021/jo982514a
日期:1999.4.1
by stannyl radicals from aryl bromides proceeds in a single step through a linear transition state whereas the abstraction of SeH from the selenols involves a T-shaped, hypervalent intermediate. Alternatively, it may be that both reactions are concerted with the bromine abstraction having a late transition state and the SeH abstraction an early one. Approximate second-order rate constants for the reaction
研究了庞大的邻位,邻位基团对芳基溴化物和十八烯醇与三丁基锡烷反应的影响。庞大的邻,邻'基团可促进溴化物与锡烷的反应,但会延迟硒醇的反应。另一方面,从头算和力场计算表明,将大量的邻位取代基引入硒醇中比相应的溴化物引起更大的应变增加。提出了两种不同反应模式的可能解释。一方面,由苯乙烯基自由基从芳基溴化物中提取溴有可能一步一步地通过线性过渡态进行,而从硒醇中提取SeH涉及一个T形超价中间体。或者,可能这两种反应都与过渡态较晚的溴萃取和早期的SeH萃取协同进行。三丁基锡烷与一系列受阻芳基溴化物反应的近似二阶速率常数来自竞争反应。2,4,6-三叔丁基苯硒固醇能够作为锡烷介导的乙烯基溴反应的适度催化剂。提出了双(2,4,6-三异丙基苯基)二硒化物的X射线晶体结构。6-三叔丁基苯硒固醇能够作为锡烷介导的乙烯基溴反应的适度催化剂。提出了双(2,4,6-三异丙基苯基)二硒化物的X射线晶体结构。6-三叔丁基苯