A series of bisethynyl compounds, IX and XII, were prepared by a modified ethynylation using N-methyl-2-pyrrolidone in good yields. Intramolecular oxidative coupling of the bisethynyl compounds has been achieved with high-dilution technique to give relatively good yields of highly strained or strainless [m.n]paracyclophadiynes I and cyclic diacetylenes XIII. From the comparison of the electronic spectra of these diacetylenic compounds, it is concluded that abnormal spectra of Ic and Id are attributed to the transannular π-electronic interaction between benzene nucleus and diacetylenic unit rather than the ring strain in the molecules. In addition, a marked down-field shift of aromatic protons in Ic compared with the other paracyclophadiynes is explained in terms of the transannular shielding effect of diacetylenic linkage.
一系列双
乙炔基化合物IX和XII通过改良的
乙炔化反应,使用N-甲基-
2-吡咯烷酮,以良好的产率制备得到。采用高度稀释技术实现了双
乙炔基化合物的分子内氧化偶联反应,得到了高张力或无张力的[m.n]型聚环对二炔I和环状二
乙炔XIII,产率相对较好。通过比较这些二
乙炔化合物的电子光谱,得出结论:Ic和Id的异常光谱归因于苯环核与二
乙炔单元之间的跨环π电子相互作用,而不是分子内的环张力。此外,与其他聚环对二炔相比,Ic中芳香质子的明显低场位移,可以用二
乙炔连接的跨环屏蔽效应来解释。