Metabolites of proteaceae. Part 9. Eximin (6-O-benzoylarbutin) and the synthesis of aryl glycoside esters

Eximin, obtained from the leaves of Protea eximia(Salisb. ex Knight) Fourcade is shown to be 6-O-benzoylarbutin, and the synthesis of its tetra-acetate from arbutin is described. A synthesis of aryl glucoside esters by glucoside formation between tetra-O-acyl-1-α-D-glucopyranosyl bromides and phenols is shown to succeed only with phenols carrying electron-withdrawing substituents. Under the same conditions phenols with electrondonating substituents promote elimination reactions leading to the corresponding glucals.