Intramolecular Cyclizations via Carbenoid Intermediates in Complexation of Alkynyltungsten Compounds with Co<sub>2</sub>(CO)<sub>8</sub>:  A New Route to the Pauson−Khand Reaction

Intramolecular Cyclizations via Carbenoid Intermediates in Complexation of Alkynyltungsten Compounds with Co<sub>2</sub>(CO)<sub>8</sub>:  A New Route to the Pauson−Khand Reaction