C-H-deprotonation mediated by a remote syn-axial acetoxy group--an unprecedented double bond formation upon cyanation of the dimer from L-fucal.
Replacement of the anomeric acetate by a cyanide group in the dimer of di-O-acetyl-L-fucal by the action of mild Lewis acid [Hg(CN)(2)-HgBr(2)-Me(3)SiCN], resulted not only in the desired transformation but also in the introduction of an additional double bond between C-2A and C-3A. Due to its configuration, the remote C-4A acetoxy group may facilitate the deprotonation by functioning as an internal base. 1H NMR spectroscopy and X-ray crystallography indicate that the conformations of both rings A and B and their relative orientation in the resulting C-linked disaccharidic glycosyl cyanide, 4-O-acetyl-2-C-(4-O-acetyl-2,3-dideoxy-alpha-L-threo-hex-2-enopyranosyl)-2,3-dideoxy-2-eno-alpha-L-fucopyranosyl cyanide, in solution are virtually identical to the crystal structure.
Franz
Andreas H
AH
Department of Chemistry, University of the Pacific, 3601 Pacific Avenue, Stockton, CA 95211, USA.
Samoshin
Vyacheslav V
VV
Myers
Chris
C
Hunter
Allen D
AD
Gross
Paul H
PH
D002236:Carbohydrate Conformation; D019281:Dimerization; D004187:Disaccharides / Q000737:chemistry*; D006027:Glycosides / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D011522:Protons
D004187:Disaccharides; D006027:Glycosides; D011522:Protons