Some aspects of the chemistry of spirophosphoranes.

A review of phosphorane chemistry is presented. A number of spirophosphoranes were synthesised with a view to establishing the relative apicophilicity of sulphur containing ligands. From this work it was concluded that the relative apicophilicities of phenylthio- and phenoxy- were very similar. In order to obtain more information on strain factors in five-membered ring phosphoranes as the ring moves from an apical -equatorial position to a diequatorial position several spirophosphoranes wore prepared containing various heteroatoms adjacent to phosphorus in the five-membered ring. It was found that when an oxygen or nitrogen heteroatom was replaced by sulphur the strain in the five- membered ring was lowered by about 3.5 kcal. mol.-1 Two new methods for the preparation of spirophosphoranes were developed and used extensively for the ring strain work and also for a series of phosphoranes from which the relative apicophilicities of phenyl, methyl and benzyl were determined. From a second series of phosphoranes, the relative apicophilicity of the dimethylamino group was determined. From other spirophosphorenes prepared, information was obtained on the relative apicophilicity of hydrogen, chlorine and p-nitrophenoxy groups. A study was made on the structure of the 1:1 adduct between hexafluoroacetone azine and trimethyl phosphite, a compound recently described in the literature. Using data obtained by chemical and physical means, including 13C n.m.r. it is proposed that the adduct is an iminophosphorane and not the three-membered ring structure proposed by the authors of the original publication.