Selenazole 4-methyl

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)],... 

In conclusion, in terms of electrophilic reactivity a methyl group in the 2-position is equally reactive in the two categories of heterocycles (selenazole and thiazole). Of the two positions ortho to nitrogen, only the 2-position is activated. The 5-position is sensitive to electrophilic reagents and resembles more closely the para position of a benzene ring. 

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... 

The investigations of Jensen and Schmith (45) indicate that in vitro activity of 2-sulfanilamido and 4-methyl-2-sulfanilamido selenazoles against pneumonia infections is comparable to that of sulfathiazole or sulfadiazine. Frisk (47) found that the activity of the selenium compounds was much lower than that of sulfathiazole. 

Diethylamino-4-methylselenazole with benzaldehvde in the same conditions as for Scheme 43 yields 2-diethylamino-4-methyl-5-phenyl-carbinyl selenazole (m.p. 254°C) (Scheme 44) (26). 

Thieno[3,2-d]selenazole, 2-methyl-synthesis, 6, 344 Thienoseleninium salts, 4, 1029 Thienoselenophenes NMR, 4, 13... 

Under comparatively mild conditions, already by the action of warm nitric-sulfuric acid, 4-methyl- and 2,4-dimethyl-selenazole were nitrated in the 5-position. 4-Methyl-5-nitroselenazole has mp 45°C, and the 2,4-dimethyl analog has mp 115-120°C (decomp. 

A methyl group in the 2-position of the selenazole ring shows the same reactivity as the analogous thiazoles toward carbonyl compounds. By reaction of 2,4-dimethylselenazole with benzaldehyde in the presence of anhydrous zinc chloride catalyst, 4-methyl-2-styryl-selcnazole (9), mp 74-75°C, could be prepared. ... 

According to investigations of Jensen and Schmith 2-sulfanil-amido- and 2-sulfanilamido-4-methyl-selenazole in vitro showed the same activity against pneumococci as sulfathiazoie. On the other hand, according to Frisk the activity of sulfamethylselenazole is very much less than that of sulfathiazoie. 

With the synthesis of the benzylidene hydrazones of selenazoles, it was possible to prepare formazans containing a selenazole ring. Of the compounds already described (Section I,C,1), 2-benzylidene-hydrazino-4,5-diphenyl- and 2-benzylidenehydrazino-4-methyl-5-carb-ethoxy-selenazole were used to couple with diazonium salts in order... 

Diethoxymethylacetate, in synthesis of, trimethine thiazolocyanines, 55 2-Diethylamino-4-methyl-5-nitro selenazole. melting point, 243... 

Diethylamino-4-methyl-5-phenvi carbinyi-selenazole, preparation, melting point. 250... 

Infrared spectra, of methyl-selenazoles, of selenazolidine, of thiazolocyanines, 75... 

Reaction of /V,/V-unsubstituted selenoureas 332 with methyl vinyl ketone in the presence of ferric chloride in refluxing ethanol gives 2-amino-5-(l -ethoxy)-1,3-selenazoles 335 <06H(68)2145>. This approach obviates the use of lachrymatory halo carbonyl compounds frequently utilized in the synthesis of 1,3-selenazoles. 

Bromination and nitration of substituted 1,2-selenazoles occurs at the 4-position but products undergo decomposition. 3-Methyl-5-phenyl-l,2-selenazole reacts with a mixture of concentrated nitric and sulfuric acids to give 3-methyl-4-nitro-5-(4-nitrophenyl)-l,2-selenazole in 54% yield, accompanied by other nitroderivatives. Bromination and nitration of 1-benzo-1,2-selenazoles results in substitution in the benzene ring and does not occur at the 3-position thus nitration afforded an almost equimolar mixture of 5-nitro- and 7-nitro-l-benzo-l,2-selenazoles in an overall quantitative yield, while bromination led to a mixture of mono-, di-, and tribromo compounds [2, 10]. 

The quaternary salts of selenium-nitrogen heterocycles are labile to nucleophiles and can be converted to other heterocyclic systems by ring expansion [82, 103], An example is conversion of 1,2,4-selenadiazolium trifluoromethane sulfonate (67) into 1,3,5-selenadiazine (68) (Scheme 17) [104], 2,3-Dimethyl-1-benzo-l, 3-selenazolium tetrafluoroborate is readily condensed with aromatic aldehydes to 2-styrylselenazole [105] or treated with sodium hydride to give 3-methyl-2-methylene-2,3 -dihydro-1 -benzo-1,3 -selenazole [106],... 

Thermodynamically stable aromatic selenaheterocycles such as selenophene (1), 1,3-selenazole (3), 1,2,5-selenadiazole (5), and 1,2,4-selenadiazole undergo [l,4]cycloaddition followed by spontaneous deselenation, which is a convenient way for construction of nonselenium azaaromatic rings [3, 6, 42], 3,4-Diphenyl-1,2,5-selenadiazole reacted with DMAD to give methyl 2,3-diphenylpyrazine-5,6-dicarboxylate. The similar reaction of 1,2,4-selenadiazoles resulted in pyrimidine -5,6-dicarboxylate, while 2,1,3-benzoselenadiazoles reacted with DMAD to give the quinoxalines [6, 110]. (For deselenation see also Sect. 5.1). 

Treatment of A-[l-(dimethylamino)ethylidene]benzenecarboselenoamide (103) with ethyl bromopyruvate in the presence of triethylamine affords 5-[(ethoxy carbonyl)acetyl]-4-methyl-2-phenyl-l,3-selenazole (104) (Scheme 31) [179], In a similar reaction of morpholino(selenocarbonyl)-amidines with 2-(chloromethyl)-5-nitrothiophene other substituted 1,3-selenazoles were obtained [180],... 

Selenazoles (72) and methyl salicylate or methyl-o-mercaptobenzoate lead to ethers (77) or thioethers (78). The acid chlorides of (77) and (78) through a Friedel-Craft cyclization afford l-benzoxepino[3,4-d]selenazoles (79) and l-benzothiepino[3,4-d]selenazoles (80), respectively (Scheme 28) (81JHC789). 

Data on the nitration of selenazoles are extremely limited. The 4-methyl- and 2,4-dimethylselenazoles are nitrated more quickly than their thiazole analogs [236],... 

Selenazolyl fulgides, 2-[5-(4-methyl-2-aryl-l,3-selenazolyl)ethylidene]-3-isopropylidene succinic anhydrides 69, were prepared by reactions of 5-acetyl-l,3-selenazoles with diethyl succinate in alcohol (Scheme 4) <2004RCI451>. 

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