Thiazoles radicals from

The radical phenylation of a large number of mono- and dialkyl-thiazoles has been investigated (393,395,396,399-405, for a general review cf. 398) and analyzed in terms of partial rate factors. As in other instances the alkyl groups slightly activate the substrate in certain positions toward phenyl radicals, but they also induce some steric hindrance to the approach of the aryl radical from the onho positions (Fig. 1-19). 

Thiazole gives a transient radical in aqueous solution upon pulse radiolysis. The radical formed under neutral conditions is the 3-hydrothiazolyl radical (201) for which electronic absorption spectra, acid-base characteristics, and second-order decay kinetics were measured. A derivative of this, the radical from thiamine (vitamin Bj) (202) was also characterized. A role is implied for related radicals (e.g., 203) during the electrochemical dimerization reported for benzothiazolium salts. ... 

Violene Radicals from Oxazoles, Thiazoles, and Selenazoles... 

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). 

These results show that in the phenylation of thiazole with benzoyl peroxide two secondary reactions enter in competition the attack of thiazole by benzoyloxy radicals, leading to a mixture of thiazolyl benzoates, and the formation of dithiazolyle through attack of thiazole by the thiazolyl radicals resulting from hydrogen abstraction on the substrate and from the dimerization of these radicals. This last reaction is less important than in the case of thiophene but more important than in the case of pyridine (398). 

The (thermal) decomposition of thiazol-2-yldiazonium salts in a variety of solvents at 0 C in presence of alkali generates thiazol-2-yl radicals (413). The same radicals result from the photolysis in the same solvents of 2-iodothiazole (414). Their electrophilic character is shown by their ability to attack preferentially positions of high rr-electron density of aromatic substrates in which they are generated (Fig. 1-21). The major... 

In agreement with the theory of polarized radicals, the presence of substituents on heteroaromatic free radicals can slightly affect their polarity. Both 4- and 5-substituted thiazol-2-yl radicals have been generated in aromatic solvents by thermal decomposition of the diazoamino derivative resulting from the reaction of isoamyl nitrite on the corresponding 2-aminothiazole (250,416-418). Introduction in 5-position of electron-withdrawing substituents slightly enhances the electrophilic character of thiazol-2-yl radicals (Table 1-57). 

The one-electron reduction of thiazole in aqueous solution has been studied by the technique of pulse radiolysis and kinetic absorption spectrophotometry (514). The acetone ketyl radical (CH ljCOH and the solvated electron e were used as one-electron reducing agents. The reaction rate constant of with thiazole determined at pH 8.0 is fe = 2.1 X 10 mole sec in agreement with 2.5 x 10 mole sec" , the value given by the National Bureau of Standards (513). It is considerably higher than that for thiophene (6.5 x 10" mole" sec" ) (513) and pyrrole (6.0 X10 mole sec ) (513). The reaction rate constant of acetone ketyl radical with thiazolium ion determined at pH 0.8 is lc = 6.2=10 mole sec" . Relatively strong transient absorption spectra are observed from these one-electron reactions they show (nm) and e... 

Benzoyl peroxide has been the most common source of phenyl radicals. But in reaction with thiazoles the benzoyloxy radical abstracts a hydrogen atom from the thiazole nucleus or from a methyl group in the case of methylthiazoles, giving by-products such as dithiazolyls or 2.2 -dithiazolylethane (183). The results obtained with benzoyl peroxide are summarized in Tables III-23, III-24. and III-25. 

Grignard reagents from, 5, 106 reactions, 5, 104 6, 274, 292 reactivity, 6, 292 synthesis, 6, 297 Thiazoles, imino-reactivity, 6, 250 Thiazoles, isopropenyl-radical polymerization, 6, 278 Thiazoles, mercapto-industrial uses, 6, 330 reactions, 5, 102 synthesis, 6, 298-299 tautomerism, 6, 247, 248, 269, 289 Thiazoles, methyl-... 

Sixteen non- to trimethyl-substituted thiazoloquinolines of these types were inveshgated under electron impact mass spectra thiazoloquinolines lose carbon monosulhde (CS) from the thiazole and HCN from both heterocyclic nuclei. When 2-methylthiazoloquinolines fragment, the hydrogen radical and a loss of a neutral... 

The products of the thermolysis of 3-phenyl-5-(arylamino)-l,2,4-oxadiazoles and thiazoles have been accounted for by a radical mechanism.266 Flash vacuum pyrolysis of 1,3-dithiolane-1-oxides has led to thiocarbonyl compounds, but the transformation is not general.267 hi an ongoing study of silacyclobutane pyrolysis, CASSF(4,4), MR-CI and CASSCF(4,4)+MP2 calculations using the 3-21G and 6-31G basis sets have modelled the reaction between silenes and ethylene, suggesting a cyclic transition state from which silacyclobutane or a trcins-biradical are formed.268 An AMI study of the thermolysis of 1,3,3-trinitroazacyclobutane and its derivatives has identified gem-dinitro C—N bond homolysis as the initial reaction.269 Similar AMI analysis has determined the activation energy of die formation of NCh from methyl nitrate.270 Thermal decomposition of nitromethane in a shock tube (1050-1400 K, 0.2-40 atm) was studied spectrophotometrically, allowing determination of rate constants.271... 

Monoalkyl aminium radicals cannot be prepared from PTOC carbamates 29 due to an equilibrium in solution favoring 2-mercaptopyridine-Ar-oxide and an alkyl isocyanate [Eq.(ll)]. With Af-(monoalkyl)thiazole-2-thione carbamates, TTOC carbamates, the equilibrium lies far to the side of the carbamate 84, and these precursors can be prepared from an isocyanate and Ar-hydroxythiazole-2-thione [Eq. (12)]. Under UV photoinitiation in acidic media, TTOC carbamates are efficient precursors for monoalkyl aminium cation radicals (Scheme 26). Monoalkylaminium radical 85 ey-clizes as efficiently as its analogous dialkylaminium radical 66, and the resulting carbon radical 86 can be trapped by a variety of radicophiles (91JOC1309) to prepare substituted pyrrolidines. 

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