Norbomadiene trimer

Similar studies of the regioselectivity in the HDA reaction between 2-substituted norbomadienes and unactivated terminal acetylenes catalyzed by a cobalt catalyst were also undertaken. Unfortunately, 2-sub-stituted norbomadienes are much less reactive with unactivated acetylenes in the cobalt-catalyzed HDA reaction than with electron-deficient olefins in the Ni-catalyzed HDA cycloadditions. When an electron-withdrawing group (Y = COOMe) or an electron-donating group (Y = OMe) is attached to the 2-position of the NBD, no desired [2 + 2 + 2] cycloadduct is observed with 1-hexyne, even in refluxing toluene for three days under the usual cobalt-catalyzed conditions (Scheme 12). Instead, some NBD dimers and acetylene trimers are detected. With a... 

Structure oxidatively to obtain the designed product. The successful synthesis started with trimerization of norbomadiene to give a mixture of syn- and anti-115 (ratio 1 3) in a total yield of 47% (Scheme 36). Treatment of syn-115 with catalyst I under an atmospheric pressure of ethylene furnished hexahydrosumanene 116 in 30% yield (based on syn-115) by ring-opening metathesis and subsequent ring-closing metathesis reactions. Finally, 2 was obtained by the oxidation of 116 with DDQ. 

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