Synthesis of cyclic phosphonate analogs of ribose and arabinose

The cyclic phosphonates of ribose and arabinose (phostones) 10-13 were synthesized by a Lewis acid-catalyzed addition of trimethyl phosphite to the partially protected D-threose 7 to give the acyclic phosphonates 8 and 9, This Abramov reaction was moderately stereoselective (3:1). A base-catalyzed cyclization of the mixture of 8 and 9 gave the four isomeric phosphonates 10-13, Two of the isomers, 10 and 11, could be crystallized from the reaction mixture, The stereochemistries of 11 and 16, the tribenzyl ether from 10, were proven by X-ray crystallography, and the stereochemistries of the other isomers and derivatives were determined by P-31 NMR chemical shift data, The X-ray data and solution NMR data indicate that these phostones and their derivatives exist exclusively in a chair conformation.