Study on the reaction mechanism of C-6 lithiation of pyrimidine nucleosides by using lithium hexamethyldisilazide as a base.
The reaction mechanism of C-6 lithiation of uridine mediated by lithium hexamethyldisilazide (LiHMDS) has been investigated. LiHMDS alone dose not lithiate at C-6 of uridine. However, in the presence of an appropriate silylating agent, e.g. trimethylsilyl chloride, the reaction of 1 with LiHMDS allowed to lithiate at C-6 and gave the corresponding C-6 silylated product 2. The experimental results shown below revealed that O-4 (N-3) of uracil moiety may be temporarily masked by silylation, which triggers the C-6 lithiation by lowering the pKa of H-6. The reaction could efficiently be applied to the synthesis of 6,5'-C-cyclouridine, a nucleoside analogue fixed in a specific glycosyl torsion angle by a carbon-carbon bridge.
D018020:Lithium Compounds / Q000737:chemistry*; D011741:Pyrimidine Nucleosides / Q000737:chemistry*; D012821:Silanes / Q000737:chemistry*
D018020:Lithium Compounds; D011741:Pyrimidine Nucleosides; D012821:Silanes; C442341:lithium hexamethyldisilazide