Abstract
The cis‐selective Wittig reaction of D‐lyxo‐pentodialdose derivative 2 with C~4~ building block 3 in the presence of NaN(TMS)~2~ as a base furnished C~9~ species 4 which was transformed into ring‐opened derivative 7; diastereoselective epoxidation of the CC double bond with MCPBA afforded the required epoxide 8. Regioselective epoxide opening via trichloroacetimino derivative 9 and cleavage of the derived oxazoline 10 led to 5‐trichloroacetylamido‐substituted compound 11 having from C‐4 to C‐9 the functions and stereochemistry found for neuraminic acid. Regioselective oxidation of the 2‐hydroxy group of 1,2,4,6‐tetra‐O‐unprotected 11 with (Bu~3~Sn)~2~O/Br~2~ afforded directly 2‐nonulose derivative 13 which adopts the pyranose form. Compound 13 could be readily transformed into the known methyl 5‐acetylamido‐3,5‐dideoxy‐D‐glycero‐D‐galacto‐2‐nonulopyranoside (19). Regioselective Cbz protection of the 1‐hydroxy group of 13 and then treatment with MeOH/HCl furnished methyl pyranoside 22. Per‐O‐acetylation and subsequent hydrogenation liberated the primary hydroxy group at C‐1, thus providing after oxidation and esterification of the carboxylic acid moiety N‐dichloroacetylneuraminic acid derivative 25. Treatment with Bu~3~SnH/AIBN afforded O‐acyl protected Neu5Ac derivative 26. The structure of 26 was confirmed by an independent synthesis from Neu5Ac. magnified image