Intramolecular [2+ 21 cycloadditions of ketene iminium salts with carbon-carbon double bonds are compared with the corresponding intramolecular [2+ 21 ketene cycloadditions. The ketene cycloaddition process provides better yields than the ketene iminium salt method for ketoketenes. However, the aldoketene iminium salts give much better yields than the corresponding aldoketenes.