SELECTIVE [3-CYCLOADDITIONS OF BETA-AMINO-ALPHA,BETA-UNSATURATED PENTACARBONYLCARBENECHROMIUM COMPLEXES TO ALKYNES - A NEW APPROACH TO FUNCTIONALLY-SUBSTITUTED CYCLOPENTADIENES(2])

3-Amino-1-ethoxyalkenylidene)pentacarbonylchromium complexes 2 react w ith alkynes in pyridine or acetonitrile to give highly substituted 5-a mino-3-ethoxycyclopentadienes 3 as formal [3+2]-cycloadducts selective ly in high yields rather than the usually favored [2+2+1]-cycloadducts , 5-methylene-2-cyclopenten-1-ones.