Betaines heterocyclic

Benzo[/)]thiophene chemistry, recent advances in, 11, 177 29, 171 Benzo[c]thiophenes, 14, 331 1,2,3-Benzotriazines, 19, 215 Benzyne, reactions with heterocyclic compounds, 28, 183 Betaines, heterocyclic derivatives of alternant hydrocarbons,... 

The various fonns of betaines are very important for their charge control functions in diverse applications and include alkylbetaines, amidoalkylbetaines and heterocyclic betaines such as imidazolium betaines. Some surfactants can only be represented as resonance fonns having fonnal charge separation, although the actual atoms bearing the fonnal charge are not ftmctionally ionizable. Such species are mesoionic and an example of a trizaolium thiolate is illustrated in table C2.3.3. 

Dipoles can also be built into heterocyclic systems, and though of limited use, they may also be utilized for the synthesis of [5,6] ring-fused systems. Reaction of 2 3H)-benzothiazolethione with (chlorocarbonyl)phenylketene in warm anhydrous benzene gave the heteroaromatic betaine (416). On heating with DMAD in boiling toluene the tricyclic pyridinone (418) was obtained, presumably by elimination of COS from the intermediate cycloadduct (417) (80JOC2474). 

Tliis chapter covers nitrogen-containing fulvalenes that can be obtained by replacement of CH=CH and/or CH, for example, types 1-3 starting from compounds 1-6. Compounds in which nitrogen atoms are arranged on the periphery of the cross-conjugated system as in 15 or 16, as well as derivatives in which the central double bond contains heteroatoms as in 17, are not included. For azoniafulvalenes of type 17 and related heterocyclic betaines see (94AFIC197). 

A detailed structural study of aza analogs of sesquifulvalene as well as other heterocyclic betaines was performed by Alcalde and coworker (89CC1086 91JOC4223), who also reviewed the pyridinium azolates class... 

Preparation of heterocyclic betaines using hypervalent Te-, I-, and Xe-reagents 99JHC1573. 

Heterocyclic Mesomeric Betaines and Analogs in Natural Product Chemistry. Betainic Alkaloids and Nucleobases... 

D. Pseudo-cross-conjugated Heterocyclic Mesomeric Betaines. 131... 

In contrast to the alkaloids mentioned so far, heterocyclic mesomeric betaines are defined as neutral conjugated molecules which can be represented only by dipolar structures in which both the negative and the positive charges are delocalized within the rr-electron system (38JCS824, 85T2239). The first heterocyclic mesomeric betaine was prepared unknowingly by Emil Fischer (1882LA316). The real structure remained unknown... 

B. Classification and Characteristic Features of Heterocyclic Mesomeric Betaines... 

This review demonstrates that representatives of all four major classes of heterocyclic mesomeric betaines were isolated from natural sources. The profound differences in the electronic structures of these distinct classes can be realized by a closer look at the canonical formulae, the frontier orbital profile, the isoconjugate relationships, physico-organic properties, and the... 

There are specific associations of various types of dipoles with the four major classes of heterocyclic mesomeric betaines, which have implications in providing a rational foundation for correlating the chemical reactions of these compounds (85T2239). Eight dipole types, systematically generated by union of the heterocations H2C = with carbanions and... 

Neooxygambirtannine (43) shown in Scheme 17 is an example of a heterocyclic mesomeric betaine belonging to class 4. This alkaloid, which is red in color, was found in Gambir and is a tanning material produced by... 

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