A study of the oxepane synthesis by a 7-endo electrophile-induced cyclization reaction of alkenylsulfides. An approach towards the synthesis of septanosides

Abstract

A procedure for the stereoselective synthesis of 2-deoxy-2-iodo- septanosides from pyranoses is reported. The procedure involves two reactions: Wittig-Horner olefination to give alkenyl sulfanyl derivatives, and electrophilic iodine-induced cyclization to give phenyl 2-deoxy-2-iodo-1-thio- septanosides (20) or 2-deoxy-2-iodo-septanosides (26a,b), in this case by subsequent hydrolysis of a phenylsulfanyl group under the reaction conditions. The seven membered ring of septanosides was only formed in moderate to low yields, preferably through a 7-endo cyclization, when an isopropylidene group was present as protecting group. The use of benzyl groups as protecting moieties in the pyranose does not afford the septanoside ring. However, when the reactions conditions were forced using more basic media, the furanoside derivatives 3 were obtained. ©ARKAT USA, Inc.