1-Hydroxysugars were dehydratively coupled with a variety of alcohols including thiophenol in the presence of a catalytic amount of ytterbium(III) triflate [Yb(OTf) 3 ] and methoxyacetic acid to give the corresponding glycosides in good to excellent yields, and in some cases, with high stereoselectivities. The reaction proceeds through selective esterification of 1-hydroxysugars with methoxyacetic
Study of the Endocyclic versus Exocyclic C–O Bond Cleavage Pathways of α- and β-Methyl Furanosides
作者:Olivier St-Jean、Michel Prévost、Yvan Guindon
DOI:10.1021/jo3027438
日期:2013.4.5
scaffolds (ribo, lyxo, arabino, and xylo) efficiently afforded acyclic thioacetals with high SN2-like selectivity at the acetal center in the presence of Me2BBr and thiophenol. The stereochemical outcome of these reactions provides important mechanisticinsights into the activation pathway of five-membered semicyclic acetals. The thioacetal products should find applications in oligosaccharides synthesis and
Two synthetic approaches to the poly(ADP-ribose) fragment via a common precursor were successfully developed. The first approach employed an indirect method that involved stepwise assembly of the ribosyl adenosine framework by O-ribofuranosylation and subsequent N-glycosylation. The second approach featured direct O-ribofuranosylation of a known 6-chloropurine riboside acceptor. The precursor was converted
A phosphine/Cu(II) complex catalyzes the dehydrative glycosylation of tri-O-benzylated 1-hydroxyribofuranose to give the ribofuranoside with high stereoselectivity. (C) 2003 Elsevier Science Ltd. All rights reserved.