Quasiphosphonium intermediates. Part 7. The preparation of trinorborn-1-yl phosphite and its reactions with halogeno compounds: stable intermediates of the Arbuzov and Perkow reactions and their structural characterization by X-ray diffraction, NMR spectroscopy, and fast atom bombardment mass spectrometry

Abstract

Trinorborn-1-yl phosphite has been prepared and has been shown to give highly stable phosphonium salts in its reactions with iodomethane and with a number of α-halogenoketones. Phenacyl bromide and p-bromophenacyl bromide underwent reaction at room temperature to give the corresponding ketophosphonium halides (Arbuzov intermediates) as the exclusive products, whilst p-nitrophenacyl chloride gave the corresponding vinyloxyphosphonium chloride (Perkow intermediate) as the first example of a stable intermediate of this type. The structures of these two types of intermediate in the solid state were confirmed by X-ray diffraction measurements which revealed distorted tetrahedral arrangements around phosphorus, with P⁺⋯ Br^– and P⁺⋯ Cl^– interionic distances of 4.58 and 4.71 Å for the phenacyl bromide and p-nitrophenacyl chloride adducts respectively. Phenacyl chloride, chloroacetone, and p-nitrophenacyl bromide gave mixed products, amongst which trinorborn-1-yl phosphate was always present. Possible reaction mechanisms are discussed. Thermal decomposition of the Arbuzov intermediates (149 °C) gave the expected phosphonates but the Perkow intermediate underwent elimination of alkyne under these conditions to give trinorborn-1-yl phosphate. ³¹P NMR and fast atom bombardment mass spectra of the quasiphosphonium salts are reported and discussed.