Mechanistic Evaluation of the Halocyclization of 4-Penten-1-ol by Some Bis(2-substituted pyridine) and Bis(2,6-disubstituted pyridine)bromonium Triflates
作者:Xi-Lin Cui、R. S. Brown
DOI:10.1021/jo000449a
日期:2000.9.1
sensitive to the nature of the pyridine, the limiting values being 3-7 except in the case of bis(2(-)-menthylpyridine)bromonium triflate where the k(-)(d)/k(2) ratio is approximately 80. The reaction of 4-penten-1-ol and its OD isotopomer with bis(lutidine)bromonium triflate was investigated to determine the deuterium kinetic isotope effect (dkie) on the bromocyclization reaction. The (k(-)(d)/k(2))(H/D)
研究了由各种双(2-取代吡啶)和(2,6-二取代吡啶)溴三氟甲磺酸(P(2)Br(+)OTf(-))介导的4-戊烯-1-醇的卤化反应取代基对反应机理的影响。在所有情况下,反应均通过两步过程进行,其中起始P(2)Br(+)可逆地解离为反应性单取代PBr(+),然后被4-戊烯-1-醇捕获以形成卤代环化产物(2-溴甲基四氢呋喃)。P(2)Br(+)(k(d))的解离速率常数对2位和6位空间位阻敏感,对于2,6-二环己基吡啶或2,6-二环戊基吡啶,P(2)Br(+)种类太不稳定,无法分离。反应性中间体(PBr(+))在反转和产物形成之间的分配比(k(-)(d)/ k(2))对吡啶的性质不是特别敏感,极限值为3-7三氟甲磺酸双(2(-)-薄荷基吡啶)溴化铵的情况除外,其中k(-)(d)/ k(2)的比率约为80。4-戊烯-1-醇及其OD异位异构体与研究了三氟甲磺酸双(吡啶)溴化铵,以确定氘对溴环化反