Organometallic Chemistry Can Simplify the Synthesis of Important Biologically Active Natural Products

The stereoselectivity of the Pauson--Khand reaction used for the construction of a 6a-carboprostaglandin is described, and a mechanistic hypothesis is proposed to explain the experimentally observed results. A further illustration of the stereoselectivity of the dicobaltoctacarbonyl-mediated cyclization of 1,6-enynes to bicyclo[3.3.0]-octenones is provided by a sequence of transformations that depicts the route to the precursors of pentalenolactone G. Further examples of the synthetic potential of the acetylene-Co$_{2}$(CO)$_{6}$ bimetalloclusters are shown by the synthesis of a vincristine model compound, and a sequence of transformations that provide strong evidence of the intermediacy of a 1,4-diyl (p-benzyne) in the collapse of a Z-diynene to an aromatic product.