An Access to the beta-Anomer of 4 '-Thio-C-ribonucleosides: Hydroboration of 1-C-Aryl- or 1-C-Heteroaryl-4-thiofuranoid Glycals and Its Regiochemical Outcome

[摘要]：We have developed a novel method for the synthesis of the beta-anomer of 4'-thio-C-ribonucleosides from 3,5-O-(di-tert-butylsilylene)-4-thiofuranoid glycal. Palladium-catalyzed coupling of 1-tributylstannyl-4-thiofuranoid glycal with iodobenzene or a heteroaryl halide gave 1-C-phenyl- or 1-C-heteroaryl-glycals. Hydroboration of these glycals proceeded at the alpha-face, and subsequent alkaline hydrogen peroxide treatment of the resulting 2'-alpha-borane furnished the respective beta-anomer of 4'-thio-C-ribonucleosides. These results demonstrate that this synthetic method has a wider scope in terms of heterocyclic base structure. During this study, unexpected Markovnikov-oriented hydroboration has been observed to lead to the respective 1'-alpha-boranes. These 1'-boranes were converted into either the ring-opened structure or the 2'-deoxy derivatives depending upon their stability.

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