The synthesis and reactions of some pentacoordinate phosphorus compounds.

The synthesis and reactions of phosphoranes are reviewed, and the mechanisms of ligand permutational isomerisms of phosphoranes are discussed in terms of Berry pseudorotations (B.P.Rs.) and Turnstile rotations (T.Rs.). The factors effecting the activation energies for these pseudorotations are discussed. The synthesis and thermal reactions of phosphoranes prepared from acyclic trivalent phosphorus compounds and from 3,4-dimethylphosphol-3-enes by using N-chlorodi-isopropylamine is described. A short investigation into the preparation of phosphoranes that contain seven-membered rings suggested that these compounds are inherently unstable. The synthesis of phosphoranes from cyclic and acyclic phosphine oxides and from phosphetan oxides by using trifluoromethanesulphonic anhydride, is described. Cis-trans isomerisations in 2,2,3,4,4-pentamethylphenylphosphetan ditriflate are discussed in terms of pseudorotations of intermediate phosphoranes. The dynamic n.m.r. spectra of certain phosphoranes were recorded and, in some cases, the difference in relative apicophilicities of phenyl, methyl and methoxyl groups were determined. The preparation of phosphoranes from alkoxyphosphetanium salts resulted in Arbuzov reactions whereas the preparation of phosphoranes from alkylthiophosphetanium salts is described and the stereospecific nature of this reaction is discussed in terms of the mechanisms of substitutions in pentacoordinate phosphorus compounds. The preparation and thermal rearrangement of 2,2,3,3-tetrakistrifluoro-methyl-5-phenyl-1,4,6-trioxa-5-phospha (5Pv) spiro [4,4] nonane, i.e. the first example of a spirophosphorane containing a 1,2-oxaphospholan ring, is described. Pseudorotations of this phosphorane are discussed. The preparation of cyclic phosphoranes, containing 1,2- -oxaphospholan rings, from epoxides and ylids is discussed and attempts to adapt this reaction to spirophosphorane synthesis is described. The preparation of chlorophosphoranes by the halogenation of allenylphosphonic dichlorides is discussed and attempts to adapt this reaction to allylphosphonates are described. In some cases this reaction lead to carbon-phosphorus bond fission. Condensation reactions using diethyl azodicarboxylate (D.A.D.) and triphenylphosphine are discussed and the use of these reagents to prepare heterocyclic compounds from diols and related compounds is described.