Cycloadditions of pentacarbonyl[(2-cyclopropyl-2-dimethylaminoethenyl)ethoxycarbene]chromium complexes 3a, prepared from pentacarbonyl [(2-cyclopropylethynyl)ethoxycarbene]chromium complexes and dimethylamine, react with alkynes to give good yields of 1-propyl- or 1-phenyl-substituted 5-cyclopropyl-5-dimethylamino-3-ethoxycyclopentadienes (6a-R′). Yields are drastically lower with any substituent other than cyclopropyl in the starting material, but are somewhat improved by formation of the chelated tetracarbonyl complexes 4 prior to cycloaddition.