Carbohydrate‐Based Crown Ethers

摘要: Chiral 12-crown-4 ethers (13–16) and 18-crown-6 (21–24) containing two three ethylene-bridged D-glucopyranose moieties, respectively, have been synthesized. 2-O-(Acetoxyethyl)-3,4,6-tri-O-benzoyl-α-D-glucopyranosyl fluoride (5), generated by treatment of 2,3,4-tri-O-benzoyl-1,2-O-ethylene-β-D-glucose (4) with HF/nitromethane/acetic anhydride was the key building block. It used as a glycosyl donor and/or – after modification an acceptor component in head-to-tail-type glycosylations. Thus, openchain precursors 9/11, 10/12, 17/18 19/20 crown were prepared from reaction 5 7, 11 12, BF3-catalyzed The stereoselectivity glycosylations could be influenced use different solvents. α-Selective syntheses 14 (from thioglycoside 11) 23 20) achieved dichloromethane using NIS/trifluoromethanesulfonic acid for activation. In acetonitrile, yielded predominantly ether 13, while 18 formed mixture α-and β-anomers 21 22 under same activation conditions.