Ring Carbon Reactivity

No systematic study of the free radical reactivity of aminothiazole derivatives has yet been reported. Their behavior, however, may be extrapolated from the detailed work performed on other thiazoles (see Chapter III. Section IX. 1). 

For ionic reactivity two cases must be considered depending on the electron demand the thiazole ring may either be electron donating or electron accepting. 

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These genera] trends direct the organization of Chapters VI and VII syntheses from the already formed thiazole ring, physicochemical studies, ambident reactivity ring carbon reactivity, main derivatives, and aminothiazole applications. 

Data on transformations of side chains are limited to the reactivity of substituents attached to ring carbons. Reactivity of the rings typically includes electrophilic substitution on heteroatoms and oxidative/reductive sequences involving variety of thiocines. 

REACTIVITY AT RING ATOMS IN PYRIDOPYRIMIDINES 2.15.3.1 Electrophilic Attack at Ring Carbon... 

The high reactivity of pyrroles to electrophiles is similar to that of arylamines and is a reflection of the mesomeric release of electrons from nitrogen to ring carbons. Reactions with electrophilic reagents may result in addition rather than substitution. Thus furan reacts with acetyl nitrate to give a 2,5-adduct (33) and in a similar fashion an adduct (34) is obtained from the reaction of ethyl vinyl ether with hydrogen bromide. 

The mode of attack of electrophilic reagents (E ) at ring carbon atoms is jS to the heteroatoms as shown, for example, in (11) and (12) the intermediates usually revert to type by proton loss. Halogenation takes place more readily than it does in benzene (Section 4.02.1.4.5). Nitration and sulfonation also occur however, in the strongly acidic environment required the compounds are present mainly as less reactive hydroxyazolium ions, e.g. (13). 

Sodium and silver pyrazole salts (Section 4.04.2.1.3(vl)) are often used Instead of neutral pyrazoles to facilitate electrophilic attack on the ring nitrogen atoms. For example, pyrazolyl-methanes (234)-(236) have been prepared from pyrazole anions (Section 4.04.2.1.3(vlll)). Unstable 2-acetyllndazoles are obtained from the reactive silver salts of indazoles (Section 4.04.2.1.3 (x)). Electrophilic attack on the ring carbon atoms also occurs more readily in... 

In the diaziridine field many compounds are known bearing N-YL, A/-alkyl and A-acyl groups, but here no dramatic changes in reactivity are caused by A-substituents. N-Aryldiaziridines are underrepresented. The ring carbon is in the oxidation state of a carbonyl compound or, in the diaziridinones (5) and the diaziridinimines (6) that of carbonic acid. In single cases, diaziridine carbon bears chlorine or fluorine. 

Pyrazolino[2,3-c][l,2,3]triazoles, 5, 702 Pyrazolium hydroxide, l,2-dimethyl-3,5-diphenylanhydro-4-hydroxy-IR spectra, 5, 201 Pyrazolium salts dequatemization, 5, 269 H NMR, 5, 185 hydrogen exchange at ring carbon, 5, 245 mesoionic compounds, 5, 171 nitrodebromination, 5, 237 reactivity, 5, 217 reduction, 5, 68, 243 synthesis, 5, 156 UV spectra, 5, 199 Pyrazolium salts, amino-reactions, 5, 262 Pyrazolium salts, bromo-nucleophilic displacements, 5, 266 Pyrazolium salts, 1,2-dimethyl-deuteration, 5, 175, 245 hydrogen exchange, 5, 71 acid-catalyzed, 5, 239 reactions... 

Reactivity of Substituents Attached to a Ring Carbon Atom. 183... 

Reactivity of Substituents Attached to Ring Carbon Atoms. 192... 

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