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DOI: 10.1055/sos-SD-001-00322

Malacria, M.; Aubert, C.; Renaud, J.-L.Science of Synthesis, (20011520.

Tris(acetylacetonato)cobalt(III), upon reduction by diethylaluminum chloride in the presence of 1,2-bis(diphenylphosphanyl)ethane, is a very effective catalyst in promoting homo-DielsAlder reactions between norbornadienes and a variety of unactivated acetylenes to afford deltacyclenes in high yields (Scheme 95).[‌40‌,‌230‌] The reactions are carried out in benzene at room temperature and the yields are influenced by the quality of the cobalt complex, which requires azeotropic drying before its use. Internal acetylenes are less reactive than terminal acetylenes and in some cases gave norbornadiene dimers as the major products. 7-Substituted norbornadienes are found to be reactive in these reactions, leading to the cycloadducts in good yields; however, low anti/syn selectivities were observed. Comparison between the efficiency of bis(acetylacetonato)cobalt(II) and tris(acetylacetonato)cobalt(III) has been made and it was observed that the rates of the cyclizations were faster with the latter reagent.

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