C-ARYL GLYCOSIDES - ELECTROPHILE INITIATED CYCLIZATIONS OF 6-ARYL-5-HEXEN-2-OLS

An approach to the synthesis of C-aryl glycosides is described. Treatment of beta-lactam 9 with N-bromosuccinimide (NBS) or N-iodosuccinimide (NIS) afforded trans-2,6-disubstituted pyrans 11a and 11b. Treatment of 9 with phenylselenenyl chloride (PhSeCl) or N-(phenylselenenyl)phthalimide (N-PSP) gave 11c and cis-2,6-disubstituted pyran 12c in different ratios depending on the reaction conditions. Treatment of beta-lactam 10 with NBS, NIS, PhSeCl, or N-PSP gave mixtures of pyrans 16 and 17. Treatment of unsaturated alcohol 24a with PhSeCl gave pyran 23a. Conversion of 23a to virenose analog 22, a C-aryl glycoside related to the chrysomycins, was accomplished using a selenoxide elimination-osmium tetraoxide oxidation sequence.