Nucleophilic Substitution Induced by Electron Transfer at the Bridgehead of Polycyclic Alkanes: Competition between Polar and Radical Pathways
作者:William Adcock、Christopher I. Clark、Neil A. Trout
DOI:10.1021/jo001638w
日期:2001.5.1
triptycenes react predominantly by a polar mechanism initiated by the formation of a carbanion. In the case of the halo ketones (6, Y = O, X = Br and I), a mechanistic divergence of the reaction was unexpectedly encountered. Whereas the bromo ketone provides the substitution product (6, Y = O, X = SnMe(3)) in good yield (ca. 75%), apparently by a radical pathway, the iodo ketone yields a fragmentation
一系列2,5(或1,4)-二氢金刚烷胺(4和5,X = Y =卤素)和9,10-二卤代三烯(7,X = Y =卤素)以及两个5-卤代(X)在不存在和存在叔丁胺(TBA)和二环己基膦(DCHP)的情况下,用THF中的Me(3)SnLi处理了金刚烷-2-酮(6,Y = O,X = Br和I)。这些反应的产物分布已通过(13)C和(119)Sn NMR光谱,气相色谱分析和GC / MS建立。前一种化合物(4和5)似乎仅通过自由基链反应(S(RN)1机理)反应生成锡取代产物。相比之下,三联体主要通过形成碳负离子引发的极性机制反应。在卤代酮(6,Y = O,X = Br和I)的情况下,意外地遇到了反应的机理分歧。溴代酮显然可以通过自由基途径以高收率(约75%)提供取代产物(6,Y = O,X = SnMe(3)),而碘代酮则可以产生碎片化产物(约95%)。产量)。这种机械转换突显了离去基团的电负性以