How Do Analogous α-Chloroenamides and α-Iodoenamides Give Different Product Distributions in 5-<i>Endo</i> Radical Cyclizations?
作者:Dennis P. Curran、David B. Guthrie、Steven J. Geib
DOI:10.1021/ja8012962
日期:2008.7.1
reaction by which the precursor is reductively deiodinated with HI. This side reaction is not available to chlorides, thereby explaining why the chlorides are better precursors in such reactions. The ability of the iodides to provide cyclized products can be largely restored by adding base. The chlorides and iodides then become complementary precursors, with chlorides giving largely cyclized/reduced products
N-烯基氨基甲酰基甲基自由基的 5-内环化提供 γ-内酰胺自由基,根据试剂和反应条件,γ-内酰胺自由基又会演变为还原或非还原(烯烃)产物。几个小组已经做出令人惊讶的观察结果,即在这种环化中,氯化物是比碘化物更好的自由基前体。这里描述了锡和氢化硅介导的 N-benzyl-2-halo-N-cyclohex-1-enylacetamides 自由基环化的详细研究。直接还原、环化/还原和环化/非还原产物的比例不仅取决于反应条件和还原剂,还取决于前体。排除了基于酰胺旋转异构体效应的前体依赖性产物比率的先前解释。前驱依赖行为被进一步分解为两种不同的影响:(1) 环化/还原产物与环化/非还原产物的比例取决于自由基前体与产物γ-内酰胺自由基反应与氢化锡竞争的能力(碘化物可以竞争,氯化物不能),和( 2) 在碘化物的情况下,大量直接还原(非环化)产物的出现归因于竞争性离子链反应,通过该反应,前体被 HI