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 31 P 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.