Amide rotamers of N-acetyl-1,3-dimethyltetrahydroisoquinolines: synthesis, variable temperature NMR spectroscopy and molecular modelling |
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Authors: | Charles B de Koning Willem AL van OtterloJoseph P Michael |
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Institution: | Molecular Sciences Institute, School of Chemistry, University of the Witwatersrand, Private Bag 3, PO Wits, 2050, Johannesburg, South Africa |
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Abstract: | Mercury(II)-mediated ring closure of N-1-(2-allyl-3-benzyloxy-4,6-dimethoxyphenyl)ethyl]acetamide 9 afforded N-acetyl-5-benzyloxy-6,8-dimethoxy-1,3-trans-dimethyl-1,2,3,4-tetrahydroisoquinoline 8. The product was shown to exist as a mixture of amide rotamers by NMR spectroscopy, since signals coalesced at higher temperatures. Variable temperature NMR spectroscopy and molecular modelling were used to investigate these rotamers and gave average values for the barrier of rotation in the range of 15-16 kcal mol−1. 2-2-1-(Acetylamino)ethyl]-6-(benzyloxy)-3,5-dimethoxyphenyl]-1-methylethyl methanesulfonate 17 was also cyclized with sodium hydride to afford the same rotameric products with the same tetrahydroisoquinoline skeleton, but as a mixture of 1,3-trans- and cis-dimethyl isomers. |
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Keywords: | isoquinolines amides mercury and compounds rotamers NMR molecular modelling |
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