Selenazoles amino

In the first chapter, devoted to thiazole itself, specific emphasis has been given to the structure and mechanistic aspects of the reactivity of the molecule most of the theoretical methods and physical techniques available to date have been applied in the study of thiazole and its derivatives, and the results are discussed in detail The chapter devoted to methods of synthesis is especially detailed and traces the way for the preparation of any monocyclic thiazole derivative. Three chapters concern the non-tautomeric functional derivatives, and two are devoted to amino-, hydroxy- and mercaptothiazoles these chapters constitute the core of the book. All discussion of chemical properties is complemented by tables in which all the known derivatives are inventoried and characterized by their usual physical properties. This information should be of particular value to organic chemists in identifying natural or Synthetic thiazoles. Two brief chapters concern mesoionic thiazoles and selenazoles. Finally, an important chapter is devoted to cyanine dyes derived from thiazolium salts, completing some classical reviews on the subject and discussing recent developments in the studies of the reaction mechanisms involved in their synthesis. 

Amino-4-aryl-5-acetic acid selenazoles were used by Knott (2l i as intermediates in the preparation of T.2, 4.6-naphthoselenazoles (21. 30, 31). 

From the point of view of reactivity, there is little difference betvv een 2-amino-selenazoles and aryl- Or alkyl-2-aminoselenazoles, except that the A"-arvl derivatives are generallv less basic and that their salts are more easily hydrolyzed. 

Nitration in the 5-position of 4-methyl- and 2,4-dimethylselenazoles with HNO3-H2SO4 is more rapid than for thiazoles [4-methyl-5-nitroselenazole. m.p. 45°C (19) 2.4-dimethyl-5-nitroselenazole. m.p. 115-120 C (decomp.) (19)]. Direct nitration of 2-amino 4-methyl-selenazole leads to nng rupture (19). 

However, prior protective acetylation of the amino group leads to a good yield of the 5-nitro compound [2-acetamido-4-methyl-5-nitroselenazole, m.p. 185 C (19)j. Similarly. 2-diethylamino-4-methy)-selenazole with nitric acid gives the. 5-nitro derivative [vellow needles, m.p. 93°C (26)],... 

As a further electrophilic substitution the bromination of selenazoles has been investigated. This is not as complicated as nitration. Bromination was carried out in several solvents and with various amounts of bromine. In spite of the great variation in conditions, monobromo derivatives containing the bromine atom in the 5-position are always formed. This could be established, for example, by the bromination of the 2-amino-4-p-nitrophenylselenazole (Scheme 34) and its 2-benzamino compound (98). The 2-benzamido bromo compound gives the same bromo... 

Much of the development of the chemistry of sulfanilamidoselenazole derivatives is a result of the important role played by sulfonamides in chemotherapy and more particularly the good activity of sulfathiazoie against bacterial infections. Backer and De Jonge (441 prepared these derivatives by reaction of 2-amino-4-methyl- and 2-aminO-4-phenyl-selenazoles with A -acetylsulfanilic acid chloride in pyridine.. Alkaline... 

Reactivity of 2-Amino Selenazoles with Ethyl Propiolate (54) and Dimethyl Acetylene Dicarboxylate... 

Alanine, ( )- -(2-amino-1,3-selenazol-4-yl)-synthesis, 6, 343 Alanine, phenyl-p-hydroxylation, 7, 565 Alanine, selenienyl-synthesis, 4, 964 Alanine, y3-2-selenienyl-applications, 4, 970 Alanine, y3-3-selenienyl-applications, 4, 970 Alanine, y3-2-thienyl-biological activity, 4, 911 Alanine, -3-thienyl-biological activity, 4, 912 L-Alanine, y-L-glutamyl-y3-pyrazolyl-occurrence, 5, 303 L-Alanine, -pyrazolyl-occurrence, 5, 303 Alanine raeemase inhibition, 1, 266 Albendazole... 

Selenazole, 2-acetamido-nitration, 6, 341 Selenazole, 2-alkyl-nitration, 6, 340 Selenazole, 2-amino-bromination, 6, 341 sulfonation, 6, 341 synthesis, 6, 342... 

Selenazol-2-inium bromide, 2-amino-X-ray diffraction, 6, 339 Selenazolin-4-ones synthesis, 6, 345... 

A variation of the general method for the synthesis of 2-amino-selenazoles is to avoid the use of the free a-halogenocarbonyl compound and in its place react the corresponding ketone and iodine with selenourea.This procedure is also taken from thiazole chemistry. By contrast with thiourea, the reaction with selenourea needs a longer reaction time and the work up of the reaction mixture is somewhat more difficult. Usually an excess of the ketone is used. In the preparation of 2-amino-4-( n-nitrophenyl)selenazole, a very high yield, calculated on the amount of iodine used, was obtained. To explain this peculiar result, the oxidative action of the nitro group was invoked. This liberates free iodine from some of the hydrogen iodide eliminated in the condensation reaction, and the free iodine then re-enters into the reaction. 

Reaction of A -substituted selenoureas with a-halogenocarbonyl compounds yields the corresponding 2-amino-selenazole substituted in... 

The 2-amino-selenazoles are crystalline compounds, and sometimes unstable, for example, the parent compound on heating in water undergoes complete decomposition. A few of these selenazoles which are substituted in the amino group are oily liquids. The basic character is more pronounced than in the alkyl- and aryl-selenazoles. The hydrochloride salts are, therefore, not so easily hydrolyzed in aqueous solution. 2-Amino- and 2-methylamino-4-methylselenazole have been considered to exist partly in the tautomeric selenazol-2-one imine form from comparison of their ultraviolet spectrum with that of 2-diethylamino-4-methylselenazole. ... 

Amino-4-aryl-selenazole-5-acetic acids were used by Knott for the preparation of naphtho-l, 2, 4,5-selenazoles. " ... 

Equally, all the attempts of Haginiwa to diazotize 2-amino-4-methylselenazole led to complete decomposition. Later these investigations were taken up by Metzger and Bailly. They tried to prepare selenazoles unsubstituted in the 2-position by means of diazo-tization and a special Sandmeyer reaction. In spite of variations in the reaction conditions, they were not able to deaminate 2-amino-4-phenylselenazole by this method. 

It has also been stated that the 5-position of selenazoles is more reactive toward electrophilic substitution than that of thiazoles. Such reactivity is still further increased by substituents in the 2-position of the selenazole ring, which can have an —E-effect. Simultaneously, however, an increasing tendency toward ring fission was observed by Haginiwa. Reactions of the selenazole ring are thus limited mainly to the 5-position which, specially in the 2-amino-and the 2-hydrazino-selenazoles, is easily substituted by electrophilic reagents. However, all attempts to synthesize selenazole derivatives by the Gattermann and by the Friedel-Crafts methods... 

Substitution of a phenyl residue in the 4-position of the selenazole ring causes only a minor alteration in the position of the absorption maximum. By contrast, the benzylidene compounds are markedly bathochromically shifted compared to the isopropylidene derivatives. Thus the absorption is caused by the whole of the conjugated system, which can be compared to that found in amino derivatives of... 

The large importance of the sulfonamides for chemotherapeutics, and specially the high activity of sulfathiazole toward bacterial infections, indicated that sulfonamido derivatives of selenazole should also be investigated. Backer and de Jonge used for this purpose 2-amino-... 

For 2-amino-4-(m-nitrophenyi) selenazole, the yield is particularly high. This has been explained by the oxidizing effect of the nitro group, which liberates iodine from the hydrogen iodide eliminated in the condensation reaction. 

Amino-4-(2-thienyI)selenazole ( n.p. 132°C. yield = 82%) also has been prepared by condensation of selenourea on 2 bromoacetylthiophene (Scheme 26). In a first step the bromhydrate is obtained (105). 

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