Layered Compounds. XVIII. Synthesis of a Paracyclophane Containing the 1,2,3,4,5-Hexapentaene Group and the Stereochemistry of Its Formation

Abstract

Abstract Novel cyclic 1,2,3,4,5-hexapentaene compounds were synthesized from cyclic diyne-diol IX via diallene-dibromide X in order to study transannular electronic interaction. A diallene-dibromide Xc-I obtained from a diyne-diol isomer IXc-I was debrominated with active zinc to give cyclic hexapentaene IIc, whereas the other diallene-dibromide Xc-II derived from the second diyne-diol isomer IXc-II was not. The X-ray crystallographic analysis of the dibromide Xc-I was then carried out, and the s-trans structure was assigned to the dibromide. On the basis of this result, the stereochemistry of the transformation from diyne-diol to the hexapentaene group was discussed. The electronic spectrum of a cyclophane IIa containing the hexapentaene group showed a transannular π-electronic interaction between the benzene ring and the hexapentaene group, unlike those of the other hexapentaene derivatives, IIc and XV.