Selenazole-5-acetic acids

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

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). 

Treatment of 2-(arylamino)selenazoles with sodium nitrite in glacial acetic acid at room temperature gives the corresponding nitroso compounds instantaneously (Scheme 381 (29). These compounds give rise to... 

Isopropylidene and benzylidene hydrazones of selenazole unsubstituted in the 5-position react with p-nitrosodimethylanilines or p-nitrosodiethyl-anilines when heated in organic solvents in the presence of acetic acid or pyridine (49). Highly colored crystalline 2-hydrazono-5-(p-dialkylamino-phenylimino)selenazoles are recovered from the reaction medium (Table X-10). 

As a further typical reaction of the hydrazine group of the 2-hydrazinoselenazoles (cf. Section I,C,2), pyrazolone formation was investigated. By condensation of the hydrazines with -ketoesters in acetic acid, it was possible to synthesize a series of l-(selenazol-2-yl)-3-alkylpyrazol-5-ones (16). ... 

Alkyl A-2-selenazolines, preparation. 259 Amidinium ion, ionic system of, 68 2-Amino-4-aryl-5-acetic acid selenazoles. 

The synthesis of A, A -disubstituted 2-amino-5-arylazo-4-phenyl-l,3-selenazoles 62 has been carried out by addition of 2-amino-4-phenyl-l,3-selenazole to an aryldiazonium salt, for example, an aryldiazonium tetrafluoroborate, in DMSO or in acetic acid (Equation 3) <2000JPR169>. 

Isopropylidene and benzylidene hydrazones of the selenazoles which are unsubstituted in the 5-position react with p-nitrosodiethyl-and p-nitrosodimethyl-aniline in organic solvents on heating and the addition of acetic acid or pyridine.32 Thus result crystalline, deeply colored, 2-hydrazono-5- (p-dialkylaminophenylimino) selenazoles (correspondingly substituted in the 4-position), details are given in Table VII. The presence of an aromatic residue in the 4-position of the selenazole ring appears to be needed to obtain crystalline compounds. 

The selenazoline 21 was the initial product of the reaction of 18 with 19. It was smoothly dehydrated to the selenazole (22) in acetic acid. 

Synthesis of 2-unsubstituted 1,3-selenazoles 24 has been reported by reactions of selenoformamides with a-bromoketones. Selenoformamides are prepared by the reaction of formamide with phosphorus selenide using ultrasound. Because of the unstable nature and volatility of 2-unsubstituted 1,3-selenazoles, the yields are relatively low, 6-28%. The cyclizations were achieved in the presence of either pyridine or an acidic ion exchange resin. The absence of base or the use of sodium acetate resulted in formation of considerable amounts of diphenacyl selenides (ArCOCH2)2Se (Scheme 6) <2005EJO3637>. 

Phenyl-2,3,5,6-tetrahydroimidazo[2,l-6]selenazole (selenotetramizole 97) is prepared by a three-step reaction sequence shown in Scheme 42. The biological activity of the (-)-isomer is comparable with that of (-)-tetramizoIe (78JMC496). The selenazolo[3,2-Z>][l,2,4]triazine system (98) is accessible from 6-substituted 3-selenoxo-2,3,4,5-tetrahydro-l,2,4-triazin-5-one by reaction with bromoacetic acid followed by treatment with acetic anhydride (Scheme 43) (71JHC1011). 

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