Abstract
Condensation of 2,4-dimethoxy pyrimidine with bromoglucosides derived from methyl 4-deoxypentopyranosides 2–7 and from 3,5,6-tri-O-benzoyl glucofuranose, 20, leads in a stereospecific manner to the nucleosides 8–13 and 22 with the trans 1′,2′ configuration. The stereochemistry of this reaction is not influenced by the structure of the starting sugar but rather is directed by the presence of the C-2 hydroxyl group. The synthesis of epoxide 18, obtained by the action of NaH on the bromohydrine 17, derived from 7, supports the intervention of a reaction assisted by an epoxide-like intermediate derived from the trans-bromohydrine. On the other hand, the cis-bromohydrine undergoes direct substitution of anomeric halogen by base. The possibility of the formation of a carbocation-like intermediate is discounted since SN1 type glycosylation reactions of 19 by MeOH or t-BuOH lead preferentially to products with the cis-configuration. [Journal translation]
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call