H-TETRAOXASPIROPHOSPHORANES AS POSSIBLE INTERMEDIATES IN THE PHOSPHONYLATION BY PHOSPHOROUS ACID/OXIRANES

The detailed 31 P-NMR study of the mechanism of the ribozymomimetic phosphonylation with phosphorous acid / oxirane revealed consecutive formation of β-hydroxy H-phosphonate monoester, di-(β-hydroxyalkyl) H-phosphonate, alkylene H-phosphonate. β-hydroxyalkyl alkylene phosphite and the corresponding stereoelectronically stabilized pentacoordinated H-tetraoxaspirophosphorane. The equilibrium between the triphosphite and the spirophosphorane shifts towards the β-hydroxyalkyl alkylene phosphite at high temperatures. In the presence of alcohol and controlled amounts of water transesterification of the β-hydroxyalkyl alkylene phosphite to the corresponding alkyl alkylene phosphite, and hydrolysis to β-hydroxyalkyl alkyl H-phosphonate proceed at the elevated temperature. β-Hydroxyalkyl alkyl H-phosphonates are model compounds of the phosphodiester bond and undergo hydrolysis with a diol leaving in the presence of one equivalent of water.