Phosphorothioates: β-Fragmentation versus β-Silicon Effect


  • The authors wish to thank Dr. T. K. Wyrzykiewicz and Dr. D. L. Cole for helpful discussions.


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β-Silylethoxy-protected phosphoramidites are useful reagents for the synthesis of O,O,O-trialkylphosphorothioates of type 1 in solution, which are interesting as building blocks for antisense oligonucleotides. Trialkylsilyl substituents in the β-position promote rapid thiono–thiolo rearrangement through neighboring group participation (β-silicon effect). Selective deprotection under mild conditions through β-fragmentation yields only O,O-dialkylphosphorothioates. T [DOUBLE BOND] N1-thyminyl.