SELECTIVE ALKYLATION OF PYRIMIDYL DIANIONS .2. SYNTHESIS, CHARACTERIZATION, AND COMPARATIVE REACTIVITY OF 3',5'-O-BIS-TETRAHYDROPYRANYL, TRIMETHYLSILYL AND TERT-BUTYLDIMETHYLSILYL DERIVATIVES OF 5-BROMO-2'-DEOXYURIDINE

Three compounds which can be used as precursors for thymidine synthesis via methylation at the 5 position, including 3', 5'-o-bis(tetrahydropyranyl)-5-bromo-2'-deoxyuridine 1a, 3', 5'-o-bis-(trimethylsily)-5-bromo-2'-deoxyuridine 1b, and 3', 5'-o-bis-(t-butyldimethylsilyl)-5-bromo-2'-deoxyuridine 1c, were prepared isolated and characterized by spectroscopic methods. Alkylation with methyl iodide using an organo-lithium reagent at low temperature produced 72%, 41% and 74% of thymidine 6, respectively. Tetrahydropyranyl and t-butyldimethylsilyl ethers are found to be better precursors for introduction of a methyl group at the 5 position.