The coupling reaction of zirconocene alkyne complexes with a second alkyne provides a general method for the preparation of asymmetrically substituted zirconacyclopentadienes. The overall transformation is the chemoselective and regioselective intramolecular cross-coupling of two alkynes, a goal that has not been achieved with other methodology. Isometrically pure 1,3-dienes or 1,3-diiodo 1,3-dienes are obtained upon treatment of the metallacyclopentadienes with aqueous acid or iodine. Because this synthesis can be carried out as a one-pot procedure starting from the alkynes and Schwartz’s reagent (Cp2ZrHCl), it is an attractive alternative to other transition-metal-based methods for the synthesis of dienes from vinyl halides and isolated vinylmetal starting materials.
“Selective, zirconium-mediated cross-coupling of alkynes: the synthesis of isomerically pure 1,3-dienes and 1,4-diiodo-1,3-dienes”, J. Am. Chem. Soc., 1989, 111(8), 2870-2874.