[2 + 2] Dimerization of norbornadiene and its derivatives in the presence of nickel complexes and zinc metal |
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Authors: | Daw-Jen Huang Chien-Hong Cheng |
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Institution: | Department of Chemistry, National Tsing Hua University, Hsinchu 300, Taiwan |
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Abstract: | Norbornadiene undergoes 2 + 2] reaction in THF in the presence of NiX2 and zinc metal powder to give an exo-trans-exo dimer and an exo-trans-exo-trans-exo trimer. In these products, the norbornadiene molecules are linked to each other by forming cyclobutane rings with all cyclobutane carbons occupying exo positions relative to the bridging carbons on the two norbornadiene fragments. Polymerization of norbornadiene occurs if the catalyst NiX2 is replaced by Ni(PPh3)2Cl2. 1,4-Dihydro-1,4-epoxynaphthalene, 5,8-dimethoxy-1,4-dihydro-1,4-epoxynaphthalene, 5-methoxy-1,4-dihydro-1,4-epoxynaphathalene and methyl 1,4-dihydro-1,4-iminonaphthalene-9-carboxylate also dimerize to give exo-trans-exo products in excellent yields in toluene in the presence of Ni(PPh3)2Cl2 and Zn powder. For the dimerization products of 5-methoxy-1,4-dihydro-1–4-epoxynaphthalene, cis and trans isomers with respect to the orientation of methoxy groups in about 1 : 1 ratio were oberved. Under similar reaction conditions for the dimerization of norbornadiene, norbornene undergoes reductive dimerization to afford a product which consists of two norbornyl groups. The structure of this product is also exo-trans-exo. |
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Keywords: | Nickel Dimerization Zinc |
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