Abstract: The cycloadducts of alkylhaloketenes and cyclopentadiene were solvolyzed in aqueous base to produce 2-alkyltropones. A competing Favorskii-type ring contraction reaction also occurs producing 6-alkyl-6-carboxybicyclo [3.1. O] hex-2-enes. The 2- alkyltropones are produced only from the endo-alkyl isomer of the alkylhaloketene- cyclopentadiene adduct, The relative amounts of 2-alkyltropone and ring contraction ...