Comparison of cationic rhodium and iridium complexes in directed homogeneous hydrogenation |
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Authors: | John M Brown Stephen A Hall |
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Institution: | Dyson Perrins Laboratory, South Parks Road, Oxford, 0X1 3QY UK |
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Abstract: | The hydrogenation of -6-methylenebicyclo2,2,2]octan-2-ol catalysed by a range of rhodium and iridium complexes has been investigated. Unlike the corresponding -alcohol, reduction is highly stereoselective leading to 95 – 99.7% of -exo-6-methylbicyclo2,2,2]octan-2-ol. Selectivity is much less pronounced for the corresponding methyl ether. Rhodium catalysts promote a competitive isomerisation of the double bond to -6-methyl-bicyclo2,2,2]oct-5-en-2-ol, of which an authentic sample was reduced in high yield to pure - product. Reduction of both -hydroxy substrates by iridium complexes is rapid and highly selective.NMR studies employing europium shift reagents played a central part in defining the stereochemical interrelationships of 2,6-disubstituted bicyclo2,2,2]octanes. |
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