A facile and stereoselective approach to geminal endo‐iodo‐exo‐bromocyclopropanes; application in the synthesis of medium‐sized rings

Abstract Geminal dibromocyclopropanes annelated to six‐, seven‐ or eight‐membered rings can be converted easily to their geminal endo‐lithio‐exo‐bromo derivatives when treated with butyllithium at −95°. Upon reaction of these derivatives with iodine at −95° the corresponding geminal endo‐iodo‐exo‐bromocyclopropanes are obtained in good yields. The structure assignments are made by means of some silver ion‐assisted ring expansions.