BASE-INDUCED CYCLIZATION OF 2-OXIMINOPHOSPHONIUM SALTS . SYNTHESIS AND SPECTROSCOPIC PROPERTIES OF 1,2,5-OXAZAPHOSPH(V)OL-2-INES

Several 1,2,5-oxazaphosph(V)ol-2-ines (4) have been prepared in high yield by basic treatment of 2-oximinophosphonium salts (3). These salts were easily obtained either by reaction of α halo ketoximes with triphenylor tri-n-butylphosphine, by oximation of the corresponding 2-keto phosphonium salts, or finally by reaction of nitrile oxides with phosphonium ylides in dimethyl sulfoxide. The reaction of desyl bromide with triphenylphosphine in benzene gave a mixture of the keto (8) and enol phosphonium (8a) salts. Treatment of 8 with hydroxylamine gave the corresponding ylide (9) instead of the expected oxime. The ring of 1,2,5-oxazaphosph(V)ol-2-ines can be opened by treatment with acids in the cold, affording the corresponding 2-oximinophosphonium salts. Thermal decomposition of 3-(4-bromophenyl)-5,5,5-triphenyl-1,2,5-oxazaphosph(V)-ol-2-ine (4d) gave 2H-3-(4-bromophenyl)azirine (10) together with triphenylphosphine oxide. The comparison of the mass spectra of 1,2,5-oxazaphosph(V)ol-2-ines with the spectra of the corresponding phosphonium salts confirmed the cyclic structure of the former. nmr spectra of the title compounds and of the corresponding salts (3) were measured in several solvents and discussed. From the chemical-shift and coupling-constant values it can be deduced that the P-O bond in the cycles (4) has high covalent character. The effect of substituents on chemical shifts and coupling constants are discussed. © 1968, American Chemical Society. All rights reserved.