Ruthenium-Catalyzed Cascade Reactions of Diynes with Norbornadiene - Synthesis of Norbornene Derivatives

Norbornene derivatives 7-11 were prepared from norbornadiene and the corresponding diynes by Ru-catalyzed [(2+2)+2] cycloaddition and subsequent transfer hydrogenation. The structure and stereochemistry of the cycloadducts were confirmed by X-ray crystal analysis. This procedure provides high diastereoselectivity to generate norbornenes 7-11 in up to 82% yield. The scope and limitations of this reaction were investigated. Compounds that contained the skeleton of 1,7-diaryl-1,6-heptadiynes were suitable starting materials. Additionally, 9h was empolyed in the synthesis of polynorbornene 31 by ring-opening metathesis polymerization (ROMP). The number-average molecular weight (M-n) and polymer-distribution index (PDI) of this new polymer were determined to be 28.6 kDa and 1.35, respectively.