Synthesis of 3- C-Branched Kdo Analogues via Sonogashira Coupling of 3-Iodo Kdo Glycal with Terminal Alkynes.

A highly efficient approach for the synthesis of 3- C-branched mono- and di-3-deoxy-d- manno-oct-2-ulosonic acid (Kdo) enyne analogues is developed for the first time based on Sonogashira coupling of terminal alkynes with 3-iodo Kdo glycal obtained by the NIS/TMSOTf-promoted one-step reaction from peracetylated Kdo ethyl ester. Further transformation of 3- C-branched mono- and di-Kdo enyne analogues by asymmetric hydrogenation and saponification provided 2-deoxy-β-carboxyl Kdo analogues in a stereocontrolled mode.