The effect of non-bonded interactions on the regioselectivity of cyclization of the hex-5-enyl radical
作者:Athelstan L. J. Beckwith、Tony Lawrence
DOI:10.1039/p29790001535
日期:——
exo-modes of cyclization of the 2,2,5-trimethylhex-5-enyl radical (10a) to be determined. Comparison of the kinetic parameters with those for the 2,2-dimethylhex-5-enyl radical (10b) and related species indicates that interaction of the pseudo-axial 2-methyl substituent with the syn-proton at C-6 disfavours the formation from (10b) of the chair-like six-membered transition state (5). The effect is, however
用三丁基锡烷处理1-溴-2,2,5-三甲基己-5-烯(9a)得到2,5,5-三甲基己-1-烯(13a),1,1,3,3-四甲基环戊烷(12a)和1,1,4-三甲基环己烷(15a)。准确确定产率使得可以确定2,2,5-三甲基己-5-烯基(10a)的内-和外-环化模式的速率常数。与那些为2,2-二甲基己-5-烯基自由基(10B)及相关物种的动力学参数的比较指示伪轴向2-甲基取代基与该相互作用顺C-6处的-质子不利于从(10b)形成椅子状六元过渡态(5)。然而,该作用太小以至于不能解释母体六-5-烯基的闭环的高区域选择性。