Organoboron monosaccharides, XVIII. Stereoselective syntheses of β‐ D ‐lyxofuranosyl glycosides

Methyl and phenyl β‐ D ‐lyxofuranoside ( 3a and 3b ) are prepared by reaction of 5 ‐ O ‐acetyl‐2,3‐ O ‐ethylboranediyl‐α‐ D ‐lyxofuranosyl bromide ( 1 ) with sodium methoxide and sodium phenoxide to give the protected glycosides 2a , b followed by deboronation and deacetylation. The protected α‐ D ‐lyxofuranosyl disaccharides 2c , d are synthesized by treatment of 1 with 1,2:3,4‐di‐ O ‐isopropylidene‐α‐D‐galactopyranose and 1,2:5,6‐di‐ O ‐isopropylidene‐α‐D‐glucofuranose after the former has been converted to its sodium organooxytriethylborate and the latter has been O ‐tributylstannylated. 2c and 2d are deboronated and deacetylated to give 3c and 3d , respectively. 2,3,5‐Tri‐ O ‐acetyl‐β‐D‐lyxofuranosyl glycosides ( 4a – d ) are obtained from 3a – d by acetylation.