2- Aminoselenazoles, synthesis

The replacement of selenoamide by selenourea in the Hantzsch s synthesis. (1st method) leads to 2-aminoselenazoles 2, 14. 15). This series of compounds has been well developed, mainlv because selenourea is much more easily accessible than the selenoamides, but also because a wide variety of a-halogenated carbonyl compounds are available for the Hantzsch s evdization reaction (Scheme 5). 2-Aminoselenazole itself was prepared from commercially available chloroacetaldehyde semihydrate... 

Ortho esters, in synthesis of symmetrical trimethine thiazolocyanines, 54 Oxazolone, for neutrocyanines, 27 Oxidation potentials, of dyes, 75 of mesosubstituted dyes, in relation with absorption, 77 of polymethine dyes, 72 Oxidoreduction, relation between sensitizers, and silver halides, 78 4-Oxo-disubstituted 2-aminoselenazoles, table of products, 262 Oxonols, nomenclature of, 26 in synthesis of dimethine neutrocyanines, 62... 

The above reaction was first reported by Hofmann. It permits the synthesis of a wide variety of compounds. By the use of suitable reaction partners, the selenocarboxamide as well as a-halocarbonyl components could be varied. The difficulty encountered in the synthesis of alkylselenocarbox-amides could be overcome by passing hydrogen selenide into a mixture of a nitrile and a-haloketone or 2-haloaldehyde acetal in the presence of condensation catalysts. [Eq. (9)]. Selenourea forms 2-aminoselenazoles. ... 

The modified Hantzsch synthesis first described by Hofmann <1889LA(250)294> has remained the general method for preparing 1,3-selenazoles. Depending on the substitution required in the selenazole the requisite selenocarboxamide and a-halocarbonyl derivatives are coupled (Scheme 7) <79HC(34)217>. Since a chlorooxirane is isomeric with an a-chlorocarbonyl, 2-aminoselenazoles are also formed with selenourea (Equation (6)) <81T2607>. The synthesis of a 5-quinonyl-l,3-selenazole... 

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