The reactivity of organophosphorus compounds. Part XXVIII. Fast, neighbouring group-induced rearrangement during alkaline hydrolysis of α-hydroxyimino-p-nitrobenzyl phosphates, phosphonates, and phosphinates

Abstract

A kinetic and product study of the fast, anchimerically assisted, alkaline hydrolysis of the 1 : 1 adducts of p-nitrobenzonitrile oxide and various phosphorus acids has been carried out. The adducts were alkyl α-hydroxyimino-p-nitrobenzyl alkylphosphonates (II; R¹= Me, R²= Me, Et. Pr, Prⁱ, Bu^tCH₂, or Bu^tCHMe) and (II; R¹= Et, Bu^t, or Ph, R²= Et), diethyl α-hydroxyimino-p-nitrobentyl phosphate (II; R¹= EtO, R²= Et), α-hydroxyiminop-nitrobenzyl diethyl- and dihexyl-phosphinate (II; R¹= R²O = Et, hexyl), and the α-hydroxyimino-p-nitrobenzyl esters of 1-hydroxy-2,2,3,4,4-pentamethyl- and -2,2,3-trimethylphosphacyclobutan-1-ones [(VII) and (VIII); X = C(:NOH)·C₆H₄NO₂(-p)]. and the corresponding esters of 1-hydroxy-3,4-dimethyl- and -3-rnethylphospholen oxides [(IX) and (X)]. In each case a t pH 7-9, it is suggested that hydrolysis proceeds via intramolecular attack by the oximinate function on phosphorus to give a pentacovalent intermediate and hence a phosphonylated benzohydroxamic acid, which via fission and a subsequent Lössen rearrangement gives p-nitroaniline and the parent phosphorus acid. These intramolecular reactions are noteworthy, not only in view of their rapidity, but also because they are not subject to steric hindrance at phosphorus, in marked contrast to bimolecular, intermolecular attack by nucleophiles. Corresponding reactions of ethyl α-hydroxyimino-p-chlorobenzylmethyl-phosphonate are also reported.