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[摘要]：The cascade reaction modes and hence the outcomes of the palladium-catalyzed oligocyclizations of various 2-bromoalka-1,(n+m+1)-diene-(n+1)-yne substrates were found to be highly dependent on the tether lengths between the multiple bond fragments, and on the nature of the substituent at the non-brominated vinylic terminus Just like 2-bromododeca1,11-dien-6-ynes with their two three-atom tethers, 2-bromotrideca-1,12-dien-7-ynes 8 and 2-bromotetradeca-1,13-dien8-ynes 17, with combinations of four-and three-as well as five-and three-atom tethers, under Heck-type reaction conditions undergo, after the initial oxidative addition step, two consecutive n-exo-dig and m-exo-trig carbopalladations followed by beta-hydride elimination and ensuing 6 pi r-electro-cyclization to furnish tricyclic bisannelated cyclohexadiene derivatives, such as 37 and 40, in moderate yields (30 and 29%). On the other hand, when 2-bromoalka-1,(n+m+1)-dienynes with a four-, five-or even a six-atom tether between the bromoene and the yne moiety, and a four-atom tether between the yne and the terminal ene unit, such as 34, 35 and 36, are subjected to Heck-type reaction conditions, they undergo a cascade oligocyclization involving a 5-exo-trigand ensuing 3-exo-trig-carbopalladation as the fourth and fifth steps before the terminating beta-hydride elimination, eventually leading to tetracyclic skeletons such as 43, 44 and 45 with a bridging three-membered ring in yields of 74, 76 and 32 %, respectively. |
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