| Abstrakt: |
The cascade reaction modes and hence the outcomes of the palladiumcatalyzed oligocyclizations of various 2bromoalka1,n+m+1dienen+1yne 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 nonbrominated vinylic terminus. Just like 2bromododeca1,11dien6ynes with their two threeatom tethers, 2bromotrideca1,12dien7ynes 8and 2bromotetradeca1,13dien8ynes 17, with combinations of four and three as well as five and threeatom tethers, under Hecktype reaction conditions undergo, after the initial oxidative addition step, two consecutive nexodigand mexotrigcarbopalladations followed by βhydride elimination and ensuing 6πelectrocyclization to furnish tricyclic bisannelated cyclohexadiene derivatives, such as 37and 40, in moderate yields 30 and 29 . On the other hand, when 2bromoalka1,n+m+1dienynes with a four, five or even a sixatom tether between the bromoene and the yne moiety, and a fouratom tether between the yne and the terminal ene unit, such as 34, 35and 36, are subjected to Hecktype reaction conditions, they undergo a cascade oligocyclization involving a 5exotrig and ensuing 3exotrigcarbopalladation as the fourth and fifth steps before the terminating βhydride elimination, eventually leading to tetracyclic skeletons such as 43, 44and 45with a bridging threemembered ring in yields of 74, 76 and 32 , respectively. |
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