An Efficient Route toward 2-Amino-β-<scp>d</scp>-galacto- and -glucopyranosides via Stereoselective Michael-Type Addition of 2-Nitroglycals
作者:Weihua Xue、Jiansong Sun、Biao Yu
DOI:10.1021/jo900609s
日期:2009.7.17
Under the catalysis of DMAP or PPY in CH2Cl2, the Michael-typeaddition of nucleophiles to 2-nitrogalactal or 2-nitroglucal leads in excellent yields and stereoselectivity to the corresponding β-galacto- or -glucopyranosides, which are ready precursors to the biologically significant β-d-galactosamine and -glucosamine units.
2-Nitro-thioglycosides: α- and β-Selective Generation and Their Potential as β-Selective Glycosyl Donors
作者:Peng Peng、Yiqun Geng、Inigo Göttker-Schnetmann、Richard R. Schmidt
DOI:10.1021/acs.orglett.5b00295
日期:2015.3.20
Michael-type addition of thiolates to 2-nitro-D-glucal or to 2-nitro-D-galactal derivatives readily provides 2-deoxy-2-nitro-1-thioglycosides. Kinetic and thermodynamic reaction control permitted formation of either the alpha- or preferentially the beta-anomers, respectively. Addition of achiral and chiral thiourea derivatives to the reaction mixture increased the reaction rate; the outcome is substrate-controlled. The 2-deoxy-2-nitro-1-thioglycosides are excellent glycosyl donors under arylsulfenyl chloride/silver triflate (ArSCl/AgOTf) activation, and they provide, anchimerically assisted by the nitro group, mostly beta-glycosides.
Convenient Glycoside Synthesis of Amino Sugars: Michael-Type Addition to 2-Nitro-D-galactal
-galactal (3) was readily accomplished starting from tri-O-benzyl-D-galactal (1) by acetyl nitrate addition to 2 and base-promoted acetic acid elimination. Addition of alcohols to 3 under conditions of base catalysis afforded 2-deoxy-2-nitrogalactopyranosides 4a–e in high yields; high α-selectivity was obtained with strong bases, whereas weaker bases furnished mainly the corresponding β-galactopyranosides