Medium-sized cyclophanes. Part XV. 10,15-Dihydro-5H-tribenzo-[a,d,g]cyclononene and analogues

Abstract

The preparation of the title compounds based on a novel cycloalkylation reaction of benzene is described. ¹H and ¹³C N.m.r. spectra support the structures. A rigid crown conformation similar to that of cyclotriveratrylene is assigned to carbocycle (IIa) and the sulphur analogues (IId and e). On the other hand, the oxygen analogue (IIc) undergoes a ready inversion between two crown forms, which can be frozen at –90°. Ketone (IIb) is also a flexible molecule. The dependence of structural parameters on the conformational mobility is discussed. The mass spectrum of the sulphone (IIe) reveals ready extrusion of water on electron impact indicating a transannular proximity effect in the nine-membered ring.