The effects of nucleophilic additives, Lewis and Bransted acids, and solvents on BF3. Et~ O- promoted cationic n-cyclizations of alkynyl-and alkenylcyclopentane-1, 3-diones are reported. The rates and selectivities of alkynyl dione cyclizations were significantly effected by the addition of external nucleophiles or water, and the regioselectivity of cyclization was effected by the choice of reaction solvent. Cyclizations of alkenyl diones, which fail under ...