Mesomeric betaines derivatives

Examples of Known Heterocyclic Mesomeric Betaines Derived from the... 

The structure of malonyl-a-aminopyridine (cf. 121) has been discussed by Snyder and Robinson/ who interpreted the infrared and ultraviolet spectra and the fact that it could be converted into a monochloro derivative (122, R = Cl) to indicate that the intra-molecularly hydrogen-bonded hydroxy form 122 (R = OH) was predominant. However, comparison of the basicities of the methoxy compound 122 (R = OMe), the mesomeric betaine 123 (R = Me), and the parent compound indicates that in aqueous solution the last exists mainly in the zwitterion form 123 (R = H), ... 

Leptopinine 82 possesses the 3,4-dihydro-isoquinolin-7-ol moiety without further conjugation and was isolated as yellow powder from Hypecoum leptocarpum after several extractions with hydrochloric acid so that this alkaloid was finally isolated as a chloride (Scheme 29). The formation of a mesomeric betaine from this dihydroisoquinoline derivative is unlikely because on addition of base no significant changes of the UV spectra were observed (99P339). A similar structure is Pycnarrhine Pycnarrhena longifolia), which was isolated as a hydroxide (81P323). 

Benzo[c]phenanthridine alkaloids are widespread in Papaveraceae, Fumariaceae, and Rutaceae. Fagaridine (118), the structure of which had to be revised, is a derivative of the unknown 5-methyl-benzo[c]phenan-thridine-8-olate (119) which is isoconjugate with the 2-methyl-chrysene anion (Scheme 43). Thus, Fagaridine is a member of class 1 of conjugated heterocyclic mesomeric betaines, which are isoconjugate with odd alternant hydrocarbon anions. 

The Apomorphine-derived alkaloid PO-3 (129) was isolated as violet needles after crystallization from acetone and ether from Papaver orientale (66MI2), but was not found in the green solutions of autoxidized apomorhine hydrochloride (62M941, 68HCA683) (Scheme 51). No anion was detected by elemental analysis. The pA"a of PO-3 is 3.88 0.02 in 50% ethanol. The IR spectrum displays no carbonyl absorption between 1650 and 1700 cm (69MI2). The UV absorption maxima of PO-3 are in agreement with the formulation of a mesomeric betaine [T-max (EtOH) = 310... 

Nitration of a series of mesomeric betaines was extensively studied in connection with their potential use as explosives (Scheme 3). Nitration of l,2,3-triazolo[2,l- ]benzotriazole 74 can be achieved selectively, occurring first at the 7-position which is followed by nitration at the 3- and 5-positions. Thus, nitration with 45% nitric acid gives a mixture of 7-nitro derivative 75 (39%) and dinitro derivative 76 (58%), while 70% nitric acid yields a mixture of 3,7- (52%), 5,7- (23%), and 3,5-dinitro (5%) isomers 76-78. Clean trinitration to 3,5,7-trinitro-l,2,3-triazolo[2,l- ]benzotriazole 79... 

Pyrazolo[l,2- ][l,2,3]triazole mesomeric betaines are generally available by an electrophilic attack of singlet nitrenes on the pyrazole nitrogen atom. When phthalazone derivative 252 is used and the nitrene is generated by reduction with triethyl phosphite, 59% yield of mesomeric betaine 253 is obtained (Equation 40) <2000T5523>. 

Thiopyran-3(6//)-ones (133 R=H or Me) are converted into 3-hydroxythiopyrylium perchlorates (134 R = H or Me) by triphenylmethyl perchlorate. Deprotonation of these salts (134) by tertiary base did not liberate the thiopyrylium-3-olates (132) but instead gave dimeric products (135 and 136) in high yield. Evidence for the transient formation of the mesomeric betaines (132) is provided by the appearance of a greenish-yellow coloration which rapidly fades. The parent betaine (132 R = H) gave exclusively the endo dimer (136 R = H) (70%). In addition to the endo dimer (136 R = Me) (75%), the 5-methyl derivative (132 R = Me) also gave a small amount of the exo dimer (135 R = Me) (6%). The dimerization (132 136) appears to be rapid and irreversible Attempts to trap the... 

Microbial oxidation of D-glucose gives calcium 2,5-diketo-D-gluconate (145) whose hydrazones (146) are converted to the betaines 148 by acid-catalyzed decarboxylation and cyclodehydralion (Scheme 6). ° Derivatives of these stable crystalline compounds have also been prepared by (i) methylation (Me2SO4) of 4-hydroxypyridazines (143) and (ii) thermal elimination of methyl iodide from 5-methoxy-l-methylpyridazinium iodides (144). 2 Irradiation of the mesomeric betaines (148) in ethanol (Hg arc lamp)... 

Like isoconjugate mesomeric betaines, which have been discussed in preceding sections, phthalazinium-l-olates (196) give 1,3-dipolar adducts with acetylenes. Thermally induced isomerization reactions of these adducts (255) make them of special interest. The A-methyl derivative and diphenyl-... 

Alkylation of 4-hydroxy-l,7-naphthyridines gives 4-hydroxy-l,7-naph-thyridinium iodides (254) which on treatment with aqueous alkali yield l,7-naphthyridinium-4-olates (253). A number of derivatives (253 R = H, CN, CO2H) have been prepared in this manner. On the basis of IR spectroscopy, the acid derivatives (253 R = CO2H) have been formulated as mesomeric betaines rather than the inner salts 255. 

The 2-nitrophenyl derivative (321 R = o-NOjC HJ on treatment with triethylphosphite gives the novel mesomeric betaine 323. 

Pyrolysis of the 2-(2-azidobenzoyl)pyridines 334 (R and R = H or Br) at llO C gives the benzisoxazoles 335, which rearrange to the mesomeric betaines 338 in good yield at higher temperatures (215°C). The yellow, crystalline betaines (v q 1640 cm ) are stable compounds whose structure is supported by an X-ray crystallographic study of the bromo derivative 338 (R = H, = Br). The following reactions of the parent system (338 R = R2 = H) have been reported (Scheme 13) (i) Nitration gives the 2-nitro... 

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