Aminophosphine oxides in a pyridine series. Studies on the cleavage of pyridine-2- and pyridine-4-yl-(N-benzylamino)-methyldiphenylphosphine oxides in acidic solutions

The synthesis and reactions of 1-(N-benzylamino)-1-(2-pyridyl)- and 1-(N-benzylamino)-1-(4-pyridyl)-methyldiphenylphosphine oxides are described. It was found that these compounds were exceptionally easy to cleave in aqueous sulfuric acid solutions to form diphenylphosphinic acid and the corresponding N-(pyridylmethyl)-benzylamines. The structure of a single diastereoisomer, that is, the (R)-(+)-1-N-(α-methylbenzylamino)]-1-(4-pyridyl)-(S)-methyldiphenylphosphine oxide was determined by X-ray crystallography. The acidic alcoholysis of the selected model chiral pyridine aminophosphine oxides was investigated by means of ³¹P NMR spectroscopy. The cleavage kinetics were also studied. On the basis of the obtained results, a mechanism of the cleavage was formulated.