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 synthesi s via methylation at the 5 position, including 3', '-o-bis(tetrahydrop yranyl)-5-bromo-2'-deoxyuridine 1a, 3', 5'-o-bis-(trimethylsily)-5-bro mo-2'-deoxyuridine 1b, and 3', bis-(t-butyldimethylsilyl)-5-bromo-2'-d eoxyuridine 1c, were prepared isolated and characterized by spectrosco pic methods. Alkylation with methyl iodide using an organo-lithium rea gent at low temperature produced 72%, 41% and 74% of thymidine 6, resp ectively. Tetrahydropyranyl and t-butyldimethylsilyl ethers are found to be better precursors for introduction of a methyl group at the 5 po sition.