亚胺,酰氯,PR 3和碱的反应生成一类新的1,3-偶极子:phospha-Münchnones。这些1,3-偶极子可以与炔烃进行环加成反应,然后损失氧化膦形成吡咯。环加成反应性取决于所采用的PR 3,其中PhP(catechyl)(catechyl = o -O 2 C 6 H 4)提供最快的环加成反应和最佳的吡咯产率。1 H,13 C和311 H NMR分析和计算表明,贫电子的炔丙基取代的亚膦酸酯和亚磷酸酯倾向于环状的1,3-偶极结构,而更多的富电子膦则更倾向于价互变异构的无环基价。X射线晶体学研究证实了这一点。密度泛函理论计算支持由不同PR 3引起的多种P-O相互作用并指出最有效的协同1,3-偶极环加成反应是针对那些其基态几何形状最像过渡态几何形状的偶极子。计算这些偶极子与带有吸电子基团的单取代炔烃的反应是通过逐步机理进行的。磷单元的存在会在1,3偶极子上产生较大的电子偏压,从而允许使
A New Use of Wittig-Type Reagents as 1,3-Dipolar Cycloaddition Precursors and in Pyrrole Synthesis
作者:Daniel J. St. Cyr、Bruce A. Arndtsen
DOI:10.1021/ja074330w
日期:2007.10.1
generate a new class of phosphorus-based 1,3-dipolar cycloaddition reagent. These substrates, which are isomeric forms of classic Wittig reagents, undergo cycloaddition reactions in an analogous fashion to 1,3-oxazolium-5-oxides (Munchnones). However, these 1,3-dipoles can be generated in one pot, in a modular fashion, and directly from available reagents, suggesting their potential general utility in