ARYL C-GLYCOSIDES .4. SYNTHESIS OF BERGENIN-TYPE C-GLUCOSYLARENES

Reaction of 1,2,3-trimethoxybenzene with 2,3,4,6-tetra-O-benzyl-beta-d-glucopyranosyl trifluoroacetate (5) in the presence of BF3.OEt2 afforded the 4-beta-C-glycosylarene 6. Hydrogenolysis of 6, then O-methoxycarbonylation, and bromination gave 1-bromo-2,3,4-trimethoxy-5-(2,3,4,6-tetra-O-methoxycarbonyl-beta-d-glucopyranosyl)benzene (9). Bromine/lithium exchange of 9 and then reaction with diphenyl disulfide furnished 2,3,4-trimethoxy-1-phenylthio-5-(2,3,4,6-tetra-O-methoxycarbonyl-beta-D-glucopyranosyl)benzene (14), oxidation of which afforded the phenylsulfinyl derivative 15. Ortho-lithiaton of 15 and then reaction with methyl chloroformate gave 2,3,4-trimethoxy-6-methoxycarbonyl-1-phenylsulfinyl-5-(2,3,4,6-tetra-O-methoxycarbonyl-beta-D-glucop? yranosyl)benzene (17). Removal of the phenylsulfinyl group from 15 with Raney nickel and then lactonisation with sodium methoxide provided 8,10-di-O-methylbergenin (2). The 3,4,11-triacette (4) of 2 had physical data that accorded with those for the natural compound.