From α‐1,2‐Anhydrosugars to C‐Glycosides: The Influence of Lewis Acids and Nucleophiles on the Stereochemistry

Ring opening of the epoxide function in α‐1,2‐anhydrosugars with alkynyl zinc and titanium compounds proceeds with retention of configuration to afford α‐C‐alkynyl‐glycosides in reasonable to good yields, while the use of the corresponding alkynyltrifluoroborates results in the formation α/β mixtures. Vinyl nucleophiles predominantly afford α‐products, whereas allyl and allenyl species almost exclusively yield β‐C‐glycosides. †This paper is dedicated to Professor Gerard Descotes on the occasion of his 70th birthday.