Catalyst and substituent effects on the rhodium(II)-catalysed intramolecular Buchner reaction |
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Authors: | Orla A McNamara N Rachael Buckley Patrick O'Leary Francis Harrington Norma Kelly Sarah O'Keeffe Angela Stack Shane O'Neill Simon E Lawrence Catherine N Slattery Anita R Maguire |
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Institution: | 1. Department of Chemistry, Analytical and Biological Chemistry Research Facility, University College Cork, Ireland;2. Department of Chemistry and School of Pharmacy, Synthesis and Solid State Pharmaceutical Centre, Analytical and Biological Chemistry Research Facility, University College Cork, Cork, Ireland |
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Abstract: | Intramolecular rhodium(II)-catalysed aromatic addition (Buchner) reactions of a range of α- and β-substituted α-diazoketones are reported. Both steric and electronic effects are evident for the aromatic additions investigated. In general, highly efficient aromatic addition is achieved through use of rhodium carboxylates bearing electronegative ligands, such as rhodium trifluoroacetate, while aromatic addition employing rhodium catalysts with more electron-donating ligands, such as rhodium caprolactam, is less efficient. Excellent levels of diastereoselectivity are possible for this process in the presence of rhodium acetate and rhodium caprolactam, however, a reduction in diastereocontrol is generally associated with use of the more reactive, electronegative catalysts. Interestingly, these catalyst effects can be overcome through the steric effects of the substituents on the α-diazoketone substrates, with the presence of sterically bulky substituents at the 2- or 3-position rendering the aromatic addition essentially catalyst independent in terms of efficiency and diastereocontrol. |
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