Isoquinolinium pseudobases

Other cation-pseudobase equilibrations that have received detailed spectral investigation include quaternary isoquinoline alkaloids and related isoquinolinium derivatives,910 naphthyridinium mono- and dications,26,38,42 44 50 pyridinium cations,51,52 isobenzopyrylium (isochro-mylium) cations,53 benzothiopyrylium (thiochromylium) cations,40 and 1,3-dithiolium cations.54 PMR spectroscopy has also been useful in the identification of pseudobases as reaction intermediates in several reactions in solution.55-57 While 13C-NMR spectroscopy is also potentially useful for the assignment of pseudobase structure, at present there do not appear to... 

There is no spectral evidence for pseudobase formation by the N-methyl-pyridinium cation in even the most basic aqueous solutions that are attainable. An oil which separates from solutions of this cation in concentrated aqueous base has been identified by PMR and IR spectroscopies as predominantly ionic N-methylpyridinium hydroxide.70 The UV spectra of the IV-methylquinolinium and N-methylisoquinolinium cations are pH-independent below pH 14, but both these cations undergo irreversible reactions in more basic aqueous solutions (Section V,D) so that pK + values are not directly measurable. Based on substituent effects in more highly substituted quinolinium and isoquinolinium cations, pKR+ values of 16.5 and 15.3 have been estimated26 for the N-methylquinolinium and Af-methyl-isoquinolinium cations respectively. The estimate for the latter cation is based on somewhat limited data and should be compared with pKR+ = 16.29, which has been measured in aqueous dimethyl sulfoxide solutions.90,91... 

If a methyl group is not present at C-1, enamine alkylation or acylation at C-4 can still be achieved using the acetone pseudobase to block the C-1 site of an isoquinolinium salt. ... 

Isoquinolinium salts can be readily converted to isoquinolones through air oxidation of the corresponding pseudobases. ... 

The ease of formation of pseudobases (carbinolamines) from a variety of isoquinolinium salts has been investigated. Increasing pH facilitates pseudobase formation. Nitidine forms a pseudobase more readily than berberine, while 6,7-dimethoxy-2-methylisoquinoline did not form a pseudobase even at pH 13.2 Sanguinarine and chelerythrine acetates exist in an equilibrium mix-... 

V. Simanek, Khim. Rast. Veshchestv., 95 (1972) through Chem. Abstr., 78, 136478e (1973). For a detailed study of pseudobase formation from isoquinolinium salts, see V. Simanek and V. Preininger, Heterocycles, 6, 475 (1977). Also O. N. Tolkachev, O. E. Lasskaya, and G. A. Maslova, Khim. Prirod. Soedin., 615 (1975) and Chem. Natural Compds., 645 (1976). 

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