Synthesis of a (2R,6R)-2-(Hydroxymethyl)-6-propa-1,2-dienyl-2H-pyran-3(6H)-one Derivative, a New Enone for the Convergent Construction of C-Glycosides of C-Disaccharides

Abstract

The previously unknown (2R,6R)-2[(tertbutyl)diphenylsilyloxy]-6-propa-1,2-dienyl-2H-pyran-3(6H)-one (16) was derived from tri-O-acetylglucal. Conjugate addition of PhSAlMe 2 to 16 followed by enolate trapping with 1,2-O-isopropylidene-3-O-methyl-a-D-xylo-pentodialdo-1,4-furanose and NaBH 4 reduction of the intermediate aldol furnished a new C-glycoside of a C-disaccharide: 4,8-anhydro-9-O-[(tert-butyl)diphenylsilyl]-6-[(5R)-1,2-O-isopropylidene-3-O-methyl-a-D-xylo-furanos-5-C-yl]-5-S-phenyl-1,2,3,6-tetradeoxy-5-thio-D-glycero-L-gulo-nona-1,2-dienitol (24). Similarly, conjugate addition of PhMe 2 SiZnMe 2 Li to 16, followed by cross-aldol reaction with 2,6-anhydro-1,3,4,5-tetra-O-[(tert-butyl)dimethylsilyl]-D-glycero-L-manno-heptose (27), and reduction gave either 4,8-anhydro-6-{(1S)-2

Recent Advances in the Synthesis of C-oligosaccharides

“…Reduction of the major aldol 25 with NaBH 4 in MeOH/THF was highly stereoselective and provided the C-disaccharide 26 in 77% yield (Scheme 6) [15].…”

“…Treatment of ketone 28 with dicyclohexylboron chloride and Et 3 N at −15 °C followed by addition of 29, the resulting aldol-borate was oxidized with 35% H 2 O 2 giving adduct 30 in 24% yield. Stereoselective reduction of aldol 30 with Me 4 NBH(AcO) 3 afforded diol 31 in 59% yield (Scheme 7) [15].…”