Iodine Catalysed Tandem Stereoselective Acetalation‐Glycosylation of Reducing Sugars Using Acetals/Ketals: Application in the Synthesis of Orthogonally Protected Nucleosides

A convenient and efficient one pot method has been developed for molecular iodine catalysed tandem synthesis of acetonide protected O‐glycosides from reducing sugars and acetals/ketals. Various free sugars reacted smoothly with both acetals and ketals to form orthogonally protected O‐glycosides in good yields at room temperature. The method works well in the presence of various external alcohols. Acetonide protected methyl ribofuranoside thus formed was utilized for the synthesis of C‐5 protected ribonucleoside derivative. One pot protection tandem glycosylation and acetonide protection of free sugars, in which both anomeric and cis‐dihydroxyl protection take place. Both acetals and ketals were employed for glycosylation and cis‐dihydroxyl protection. The methodology was used to lock ribose in furanoid form used as donor for the synthesis of orthogonally protected nucleoside.