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DOI: 10.1055/sos-SD-001-00322

Malacria, M.; Aubert, C.; Renaud, J.-L.Science of Synthesis, (20011519.

The cobalt-substituted buta-1,3-dienes of type 80, generated from the cobaloxime anion 78 and allenes or enynes (see Scheme 55),[‌206‌,‌207‌] react with a large variety of dienophiles under mild conditions and with high regioselectivity to produce air and thermally stable, crystalline, cobalt-substituted cyclohexenes in good yields.[‌206‌] Indeed, the complexes 80 exist predominantly in a conformation close to s-cis, owing to steric interactions between the diene and the dimethylglyoximato ligands, and hence they participate in DielsAlder reactions under mild conditions (Scheme 94). Thus, all cycloadditions are carried out in refluxing tetrahydrofuran with a slight excess of dienophile. All the symmetrical dienophiles react to afford a single adduct, whereas gem-disubstituted dienophiles produce mainly para-products in good yields and with good to excellent regioselectivity. In these latter cases the regiochemical results are quite comparable with those of other thermal DielsAlder reactions for dienes substituted with electron-donating groups in the 2-position.

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