Lari, A, Pitak, Mateusz, Coles, Simon J., Rees, Gethin, Day, S.P., Smith, M.E., Hanna, J.V. and Wallis, J.D.
Models for incomplete nucleophilic attack on a protonated carbonyl group and electron-deficient alkenes: salts and zwitterions from 1-dimethylamino-naphthalene-8-carbaldehyde
Organic & Biomolecular Chemistry, 10, (38), . (doi:10.1039/C2OB25929J).
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The X-ray crystal structures of salts and zwitterionic Knoevenagel products from 1-dimethylamino-naphthalene-8-carbaldehyde show long N-C bonds between peri-groups which provide models for incomplete nucleophilic attack on a protonated carbonyl group and electron-deficient alkenes respectively. For the salts the N-C bonds lie in the range 1.625-1.638 angstrom with C-OH bonds intermediate in length between single and double bonds, while for the zwitterions the N-C bonds lie in the range 1.612-1.660 angstrom. The structural assignment of the former is supported by solid state C-13 and N-15 NMR studies on doubly isotopically-labelled material. Several zwitterions were converted to naphtha[1,8-bc]azepines by a mechanism involving the tertiary amino effect.
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