DIASTEREOMERIC 5,6-DIHYDROTHYMIDINES - PREPARATION, STEREOCHEMICAL ASSIGNMENTS, AND MNO2 OXIDATION STUDIES TO THYMIDINES

A useful method for the stereospecific synthesis of beta-thymidine and beta-5,6-dihydrothymidine nucleosides is described. Condensation of m ethyl 2-formylpropionate and methyl methacrylate with oxazolines 8 fur nished the corresponding 2,2'-anhydrothymidine 11 and a 2:1 diastereom eric mixture of 2,2'-anhydro-5,6-dihydrothymidine 10, respectively. Wh ile DDQ oxidation of 10 furnished 11, active MnO2 resulted in a select ive dehydrogenation hitherto unreported in nucleoside chemistry. The m inor diasteromer 10b was quantitatively converted to 11, leaving 10a u nchanged. A plausible explanation for this selectivity was based on th e stereochemistry at C5 which was determined by one-dimensional NOE st udies.