H-tetraoxaspirophosphoranes as possible intermediates in the phosphonylation by phosphorous acid/oxiranes

The detailed P-31-NMR study of the mechanism of the ribozymomimetic phospho rylation with phosphorous acid / oxirane revealed consecutive formation of beta -hydroxy H-phosphonate monoester, di-(beta -hydroxyalkyl) H-phosphonat e, alkylene H-phosphonate, beta -hydroxy alkyl alkylene phosphite and the c orresponding stereoelectronically stabilized penracoordinated H-tetraoxaspi rophosphorane. The equilibrium between the triphosphite and the spirophosph orane shifts towards the beta -hydroxyalkyl alkylene phosphite at high temp eratures. In the presence of alcohol and controlled amounts of water transe sterification of the beta -hydroxyalkyl alkylene phosphite to the correspon ding alkyl alkylene phosphite, and hydrolysis to beta -hydroxyalkyl alkyl H -phosphonate proceed at the elevated temperature. beta -Hydroxyalkyl alkyl H-phosphonates are model compounds of the phosphodiester bond and undergo h ydrolysis with a diol leaving in the presence of one equivalent of water.