Synthesis and Structural Peculiarities of Homeomorphic Phosphorus Bridgehead Macrobicyclic Compounds and Novel Dioxaphospha[3.1.1.]p,m,p-cyclophanes

The double‐capping reaction of p,m,p‐trinuclear diphenol 4 with PCl3 affords the three homeomorphic isomers 5–7 of a phosphite macrobicyclic compound in low yields. X‐ray structures of out,out‐isomer 5 and in,in‐isomer 6 show very flat macrobicyclic structures with P–P distances of 4.9 Å and 4.5/5.3 Å (two conformers), respectively. The main product of the reaction, however, appears to be diphosphite 8, which contains two dioxaphospha[3.1.1.]p,m,p‐cyclophane subunits. The structural peculiarities of 8 were studied after subsequent oxidation to the corresponding phosphate 12. At room temperature the free rotation either of the para‐phenylene rings and the meta‐phenylene ring in the macrocyclic moieties are hindered as could be demonstrated by means of NOESY measurements. The latter occupies an angled position in respect to the macrocyclic plane. This leads to the existence of conformational isomers due to different relative positions of the meta‐phenylene ring to the P‐OR substituent (cis,trans). We could isolate the cis,cis‐isomer of 12 and establish its structure by X‐ray diffraction. The double‐capping reaction of a flexible 1,3‐phenylene diphenol with PCl3 affords the three homeomorphic isomers of a P‐bridgehead macrobicyclic compound, one example of which is shown here. However, the main product after subsequent oxidation is a novel diphosphate containing two slightly strained dioxaphospha[3.1.1.]p,m,p‐cyclophane subunits. In these heterocycles the rotation of both para‐ and the meta‐phenylene rings is hindered giving rise to the existence of relatively stable cis,trans‐conformers due to different relative positions of the central meta‐phenylene ring to the POR group.