Ferrier rearrangement promoted by an electrochemically generated zirconium catalyst
摘要:
In situ generated zirconium catalyst from a sacrificial zirconium anode was successfully applied to promote Ferrier rearrangement of 3,4,5-tri-O-acetyl-D-glucal and 6-deoxy-3,4-di-O-acetyl-L-glucal (3,4-di- O-acetyl-L-rhamnal) in the presence of three thiols and eleven thiophenols as nucleophiles. A simple constant current electrolysis (20 mA, 0.4 F mol(-1)) of an acetonitrile solution of lithium perchlorate (0.1 M) containing the corresponding glycal and S-nucleophiles, using a zirconium anode and a platinum cathode resulted in the successful synthesis of the corresponding 2,3-unsaturated peracetylated thioglycosides (with an average anomer ratio alpha/beta-4.129 in the case of peracetylated D-glucal and 8.740 in the case of L-rhamnal). The same procedure proved to be appropriate in synthesizing dihydropyran derivatives ('C-glycosides') using allyltrimethylsilane as the nucleophile (only 'alpha-anomers' were obtained). All new compounds were fully characterized by spectral data, whereas single-crystal X-ray analysis was performed for two thioglycosides. (C) 2015 Elsevier Ltd. All rights reserved.
An efficient and divergent approach to C(2)-C(3) unsaturated glycosyl and a-p-mannopyranosyl sulfones has been developed via ruthenium-promoted direct glycosylation, oxidation, and dihydroxylation from glycal in one-pot. The presence of stoichiometric amounts of NaIO4 and in situ generation of RuO4 from a RuCl3-NaIO4 reagent system were crucial for chemoselective oxidation of sulfide in the presence of an olefin moiety. The dual-role of ruthenium in sequential glycosylation-oxidation-dihydroxylation is amenable to a wide range of thio acceptors to access alpha-n-mannopyranosyl sulfones in good yields with high regioselectivity.