Reaction of N³-benzoyl-3′,5′-O-(di-tertbutylsilanediyl)uridine with hindered electrophiles: Intermolecular N³ to 2′-O protecting group transfer

The compound N³-benzoyl-3′,5′-O-(di-tert-butylsilanediyl)uridine 2 was alkylated with various alkyl iodides in CH3CN in the presence of base. Normal 2′-O-alkylated products were obtained with methyl or benzyl iodide. If hindered alkyl iodides with β-branching such as 2-ethylbutyl iodide were used as electrophiles under the same conditions, N³-alkyl-2′-O-benzoyl uridine derivatives were produced. This unexpected transformation is usually dormant with reactive alkylating agents, but expressed with sterically hindered, less reactive electrophiles. This unwanted reaction gives isomeric products whose spectra differ in only subtle ways from target compounds.