Photochemical Synthesis of Phosphinolines from Phosphonium−Iodonium Ylides

We describe three different series of experiments which were undertaken to test our hypothesis that during irradiation of phosphonium−iodonium ylides (1a, 1b) an electrophilic carbene is generated. By opposing the assumed intermediate to monosubstituted alkynes, we observed in the case of electron-rich substituents at the triple bond a domination of a 1,3-dipolar cycloaddition of the intermediate with the triple bond to yield furans. In the case of electron poorer substituents, the formation of phosphinolines prevails. A second series of experiments was carried out with mixed ylides in which one phenyl ring at the triarylphosphonium group was replaced by a thienyl group. In this case, we observe only an intramolecular reaction with the thienyl ring to yield the phosphinolines 21−23. In a third test, we replaced in the mixed ylides 1a, 1b the COR group by a CN substituent. This modification leads to phosphinolines only and avoids a 1,3-dipolar cycloaddition.本研究设计了三组独立的实验系列，以验证我们提出的假说：鏻-碘鎓叶立德(phosphonium−iodonium ylides，1a、1b)受辐照时，会生成亲电卡宾(carbene)。将所推测的亲电卡宾中间体与单取代炔烃进行反应，我们观察到：当炔烃三键连有给电子取代基时，中间体与三键发生1,3-偶极环加成(1,3-dipolar cycloaddition)反应的路径占主导，最终生成呋喃类产物；而当取代基为吸电子取代基时，生成磷啉(phosphinolines)的反应路径占据优势。 第二组实验采用混合叶立德开展，该类叶立德的三芳基鏻基团上的一个苯环被噻吩基(thienyl group)取代。在此实验条件下，仅观察到中间体与噻吩环发生的分子内反应，最终生成磷啉(phosphinolines)21~23。 第三组实验中，我们在混合叶立德1a、1b中将COR基团替换为氰基(CN)取代基。该结构修饰仅会生成磷啉(phosphinolines)，且完全避免了1,3-偶极环加成(1,3-dipolar cycloaddition)反应的发生。