4-aryl-5-tosyloxyhexanoates are converted to mixtures of lactones when exposed to silica or heated with p-toluenesulfonic acid in various solvents. The aryl ring must have an EWG for the reaction to proceed. A similar reaction occurs with 4-aryl-5-tosyloxypentanoates, but in this case only -lactones are formed. Suggest a mechanism that accounts for both the observed regioselectivity and stereoselectivity and the requirement for an ERG on the aryl ring