1,6-Diynes norbomadienes

Itoh and coworkers carried out tandem [2 - - 2 - - 2]/[4 - - 2] cycloadditions catalyzed by a ruthenium catalyst. The reaction of diyne 147 with excess norbomene 148 in the presence of ruthenium catalyst 153, for example, afforded 149. Adduct 150 either dissociated from the catalyst or reacted with anotoer equivalent of norbomene. In the latter case, a ruthenium catalyzed Diels-Alder reaction occurred, affording hexacyclic adduct 152 via 151 (equation 43). Compounds 150 and 152 were obtained in yields of 78% and 10%, respectively. Both cycloaddition reactions proceeded with complete stereoselectivity. When 1,6-heptadiyne was used instead of 147, only trace amounts of a cycloadduct were obtained. Replacing norbomene by norbomadiene, which was expected to result in polymer formation, did not afford any adduct at aU. 

Generally speaking, Schrock initiators are highly active in the ROMP of a vast variety of cyclic alkenes such as substituted NBEs, norbomadienes, 7-oxanorbornenes, cyclooctatetraenes (GOTs), 1,4-CODs, etc., or polycyclic alkenes such as certain quadricyclanes. In addition, they may be used for 1-alkyne polymerization and the cyclopolymerization of 1,6-hepta-diynes. Despite the fact that they are highly sensitive... 

One important use for ruthenium catalysts is in cycloaddition reactions. A Ru-catalyzed cascade reaction of norbomadiene 12 with diynes 13, furnishing nor-bomene derivatives 14, was reported by Cheng et al. (Scheme 5.6) [13]. The process involves Ru-catalyzed [ 2+2)+2] cycloaddition and transfer hydrogenation. 

SCHEME 5.6 Ru-catalyzed cascade reaction of norbomadiene and diynes. 

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