Cross-conjugated mesomeric betaines

Oxidation of berberine (49) with hot dilute nitric acid yields berberidic acid (220) (58MI1) which can form a cross-conjugated and a pseudo-cross-conjugated mesomeric betaine on deprotonation as shown in Scheme 72. 

Methylisoquinolinium 2-carboxylate (230), originally prepared by Quast (70LA64), was recently identified as a defensive betaine from Photuris versicolor fireflies (99JNP378). It is a pseudo-cross-conjugated mesomeric betaine isoconjugate to the odd alternant hydrocarbon 2-isopropenyl-naphthalene anion which is an odd alternant hydrocarbon anion. This compound therefore is a member of class 13, which is very rare. The UV absorption maxima Imax (methanol) were found at 235 (4.35), 320 (shoulder, 3.97), and 326 (3.99) nm. This compound undergoes similar reactions as Homarine 19 (Scheme 75). The NMR data are presented in Table VIII. 

Quaternization of harman (235) with ethyl bromoacetate, followed by cyclization of the pyridinium salt 236 with 1,2-cyclohexane-dione in refluxing ethanol yielded an ester which on hydrolysis gave the pseudo-cross-conjugated mesomeric betaine 237. Decarboxylation resulted in the formation of the alkaloid Sempervirine (238). The PCCMB 237 is isoconjugate with the 11/7-benzo[u]fluorene anion—an odd nonalternant hydrocarbon anion—and belongs to class 14 of heterocyclic mesomeric betaines (Scheme 78). 

Vincarpin and Dihydrovincarpin are two additional examples of pseudo-cross-conjugated mesomeric betaines. They were isolated from Vinca major elegantissima (76TL4887) (Scheme 82). 

Structurally related to Nigellicine (234) (cf. Scheme 77) which is a pseudo-cross-conjugated mesomeric betaine. 

Oxidation yields the cross-conjugated mesomeric betaine 217, but no zwitterionic species, which would result by deprotonation of the indole NH group (88LA1111). The corresponding 5,6-unsaturated indole, however, gave the zwitterion. The same publication describes a total synthesis of Flavoserpentine. 

Synthesis of Cross-Conjugated and Pseudo Cross-Conjugated Mesomeric Betaines... 

Synthesis of cross-conjugated mesomeric betaines containing l-oxo-l//-pyrazolo[l,2-tf]pyrazol-4-ium-3-olate, 1-oxo-1 //-pyrazolof 11.2,4]triazol-4-ium-3-olate, 7-oxo-7//-pyrazolo[l,2-tf][l,2,4]triazol-4-ium-5-olate, 7-oxo-7.//-pyrazolo[ 1.2-//][ 1.2.3 ]mazol-4-ium-5-olate, 3-oxo-3//-pyrazolo[l,2- ][l,2,3,5]thiatriazol-8-ium-l-olate, and 2-hydroxy-pyrazolof 1.2-//][ 1.2.5]m.izin-5-iumH-olate structures was duly covered in CHEC-II(1996) <1996CHEC-II(8)747> and... 

Cross-conjugated mesomeric betaine - Cross-conjugated heterocyclic mesomeric betaines are cyclic mesomeric betaines in which the positive and negative charges are exclusively restricted to separate parts of the Tt-electron system of the molecule <1985T2239>. For examples see Sections 2.2.1.2.2 and 2.3.1.2.1. 

Figure 5 Cross-conjugated mesomeric betaines (1,4-dipoles).

Conjugated mesomeric betaines 8.31.2.1 3 Cross-conjugated mesomeric betaines 8.31.2.1.4 Fully saturated compounds... 

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