THE PAUSON-KHAND-REACTION ON ENYNES BEARING A PENTACARBONYLMETAL (CR,W)CARBENE TETHER

The study of the scope of the Pauson-Khand reaction on alkynyl(allylam ino)carb ene pentacarbonyl complexes of chromium and tungsten(0) is re ported. This reaction affords good yields of the expected cycloadducts under very mild conditions and short reaction times. One of the featu res of this process is that the metal pentacarbonyl moiety remains in the final products. Substitution at different sites of the enyne chain shows a considerable influence of both steric and electronic effects in the overall reaction course. In this way, new cobalt carbene comple xes are obtained and fully characterized. The effects of the presence of different heteroatoms in the enyne chain are also studied. A survey on the factors responsible for an easy intramolecular cycloaddition a nd a mechanistic proposal are also described. This study points to the geometry of the almost exclusive isomer formed in the aminolysis of t he precursors 1 as the decisive (but not the only one) facilitation fa ctor.