Allobetulin (3a) and allobetulin acetate (3b) were efficiently prepared in excellent yield from betulin (2a) and betulin 3-acetate (2b) catalysed by a number of solid acids in refluxing dichloromethane. Sulfuric acid on silica, montmorillonite clays (both K10 and KSF), kaolinite, bleaching clay and toluene--sulfoni