Mechanism & stereochemistry of some reactions of iv- & v- co-ordinated phosphorus compounds.

A series of cyclic phosphoranes and spirophosphoranes have been prepared and reacted with diethyl phosphorochlor- idite, the phosphorane acting as a nucleophile, and the subsequent products reacted further with methyl iodide and chloral. Reactions have also been carried out in which a nucleophilic attack on the phosphorane occurs, the nucleophile employed being the anion of thio-phenol. It was hoped these reactions might provide a new pathway to the type of phosphorus compound which have been involved for a number of years in the control of pestsoniiosects and that an insight into the stereoelectronic requirements of reactions at phosphorus might be obtained. The mechanism of the Michaelis-Arbusov rearrangement is generally accepted as having a two stage pathway, the second stage usually considered as being an SN2 attack of a nucleophile on the a-carbon of an alkyl group. Arbusov and related reactions with unsymmetrical phosphites containing different alkyl groups have been carried out. The effect of varying the electrophile, nucleophile, temperature and solvent of the reactions has been studied. As a result of the above, the second stage of the generalised Arbusov reaction is found to have SNl character. The stereochemistry of nucleophilic substitution at phosphoryl centres has been studied extensively by a number of groups. However, it has not hitherto been possible to investigate the stereochemistry of hydrolyses since these lead to achiral acids. A general method, involving isotopic labelling, has been developed that allows the stereochemistry of such hydrolyses to be established. The stereochemistry of the alkaline hydrolyses of Sp-methyl methylphenylphosphinate and methylphenylthiophosphinate have been established using the method referred to above.