Isoquinolinium betaines

The addition of DMAD to the isoquinolinium betaine 369 gave the interesting cycloadduct 370.397 A 1,4-cycloaddition and Diels-Alder reaction took place when 4-dithiocarboxyl-2,3-dimethylisoquinolinium betaine (371) was heated with DMAD in DMF for 20 to 30 minutes at 100°. The initial product was thought to be 372, which added a second mole of ester yielding 373.398... 

A soln. of N-benzhydryldichloromaleimide in glacial acetic acid treated with a soln. of excess isoquinoline in glacial acetic acid at 100-110° for 1 hr. 2-(N-benzhydryl-2-oxy-3-maleimidyl)isoquinolinium betaine. Y 94%. F. e., also with equimolar amounts in the presence of triethylamine, which does not react under the above conditions, s. M. J. Karten et al., J. Org. Ghem. 30, 2657 (1965). 

Methanolic N KOH added dropwise with stirring to a soln. of phenacylisoquino-linium bromide and benzalacetophenone in methanol crude N-(l,3,5-tri-phenyl-l,5-pentanedion-2-yl) isoquinolinium betaine. Y 74-96%. F. e. s. W. Zecher and F. Krohnke, B. 94, 690 (1961). 

In general, the A -methyl derivative of a given compound absorbs at longer wavelengths than the O-methyl derivative. The intensity of a band which appears in aqueous solutions beyond the maximum absorption in alcohol and which is due to the absorption of the betainic species alone, is a measure of the tautomeric equilibrium. The pA"a value of the 2-methyl-hydroxyisoquinolinium chlorides increase in the order 4-hydroxy (4.93), 8-hydroxy (5.81), 6-hydroxy (6.02), 5-hydroxy (6.90), and 7-hydroxy (7.09 in water at 25 °C, respectively) (57JCS5010). Thus, 2-methyl-4-hydroxyisoqui-nolinium chloride is the strongest acid. The UV spectra of 2-methyl-isoquinolinium-5-olate (34) and 2-methyl-isoquinolinium-8-olate (39) were also presented (61BCJ533) and the formation of a quinoid structure of 2-methyl-isoquinolinium-6-olate (38) can also be detected by means of UV-spectroscopy. 

The yellow-orange Neooxyberberine (52) (9,10-dimethoxy-5,6-dihydro-[1,3]dioxolo[4,5-g]isoquino[3,2-u]isoquinolinium-l 3-olate phenolbetaine of Berberine , 13-hydroxyberberinium phenol-betaine ) was already... 

The preceding sections demonstrate two important general routes to six-membered heterocyclic mesomeric betaines. These are (i) deprotonation of appropriate quaternary salts and (ii) valence tautomerism of bicyclic isomers. Both approaches have been used to prepare isoquinolinium-4-olates (170) (Scheme 7). 

Indano[l,2-6]aziridin-6-ones (171), which have been prepared by three different routes,are converted to isoquinolinium-4-olates (170) by either photolysis or thermolysis. The betaines (170) have not been... 

Nucleophilic intramolecular addition of a carbon-silicon bond onto a carbon-nitrogen iminium ion is the key step of a berbine synthesis <82CC769,83H(20)417>. Thus, treatment of the isoquinolinium salt (235) with caesium fluoride in ethanol afforded (+)-xylopinine (237), presumably via the betaine (236) (Scheme 45). A silicon-directed intramolecular cyclization of a A-acyliminium ion (238) was also the key step of Speckamp s synthesis of (+)-epilupinine as shown in Scheme 46 <85JOC40I4>. 

Formylphenyl)ethanal 38 and analogous dicarbonyl compounds undergo cyclization with ammonia to give isoquinolines. Primary amines produce A -substituted isoquinolinium ions, hydroxylamine yields isoquinoline A -oxides, and hydrazines give isoquinolinium A -betaines ... 

Thiazolo[2,3-a]isoquinolines.—[CaNS-CsN-Ce]. The conversion of N -benzylisoquinolinium bromides (312) into mesoionic 3-phenylthiazoIo-[2,3-a]isoquinolinium-2-thione betaines (313) by carbon disulphide in alkaline aqueous dioxan has been re-investigated. > iV-Benzyliso-quinolinium 4-dithiocarboxylates (314) are formed as by-products. ... 

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