3-Hydrazino-2 quinoxalines

Note Many of the (substituted hydrazino)quinoxalines covered in this section have been converted into metal complexes, randomly exemplified here. 2-(Pyridin-2-ylhydrazonomethyl)quinoxaline (246) Fe(ll), Ni(ll), and Cu(ll)... 

Chloro-2-[A -methyl-Af -(thien-2-ylmethylene)hydrazino]quinoxaline 4-oxide (288, R = H) with 2-chloroacrylonitrile gave 8-chloro-4-hydroxy-l-methyl-... 

Chloro-2-(iV-methy]hydrazino)quinoxaline 4-oxide gave 6-chloro-2-[lV -(fur-2-ylmethylene)-lV-methy]hydrazino]- (232, X = O) (2-furaldehyde, dioxane, reflux, 1 h >95%)473 or 6-chloro-2-[iV-methyl-iV -(thien-2-ylmethylene) hydrazinojquinoxaline 4-oxide (232, X = S) (2-thiophenecarbaldehyde, dioxane, reflux, 1 h 91%).515... 

Various 3-substituted aminoquinoxaline-2-thiones have been prepared from quinoxaline-2,3-dithione. For example, treatment of the dithione with methylamine yields 3-methylaminoquinoxaline-2-thione, and the corresponding reaction with hydrazine hydrate yields 3-hydrazino-quinoxaline-2-thione. The latter compound is also obtained by treatment of 2,3-dichloroquinoxaline with thiourea and then with hydrazine hydrate. When 2-chloroquinoxaline 1-oxide is heated with thiourea in methanol at room temperature, an unidentified solid m.p. 184-185° is obtained alkaline hydrolysis of methanol-soluble products gives quinoxaline-2-thione in 41% yield. A method of some general applicability is illustrated by the preparation of the thioxo compound 4 from o-anilinoaniline (3). °... 

Chloro-1 -methyl-3-trifluoromethyl- //-[ 1,3,4]oxadiazmo[5,6-fc]quinoxaline (570) suffered thiolytic ring fission in refluxing pyridine (containing phosphorus penta-sulfide) during 1 h to provide 7-chloro-3-[7/-methyl-A( -(triiluoroacetyl)hydrazino]-2(17/)-quinoxalinethione (571) in 87% yield. ... 

Hydrazino-, hyrazono-, and derived quinoxalines are often used for cyclization that may or may not involve annulation of the quinoxaline system. The following examples are classified according to the type of product, initially a few typical azahetarylquinoxalines and then some (annulated) azahetarenoquinoxalines. 

Benzoyl-l-ethoxycarbonylethylidene)hydrazino]-2(l//)-quinoxalinone (284) gave 2-phenacyl- //-[ 1,2,4]triazino[4,3-a]quinoxaline-1,5(6/f)-dione (285)... 

Chloro-2-fluoroquinoxaline 6-C hloro-7-fluoro-2,3( I //, 47/)-quinoxalincdionc 6-Chloro-2-(hex-1 -ynyl)quinoxaline 2-Chloro-3-hydrazino-6-methoxyquinoxaline 6-Chloro-2-hydrazino-3-methoxyquinoxaline 6-Chloro-3-hydrazino- l-mcthyl-2(l //)-... 

Ethyl-3-hydrazinoquinoxaline Ethyl 3-hydrazino-2-quinoxalinecarboxylate 2-(l-Ethylhydrazino)quinoxaline 4-oxide A -Ethyl-3-hydroxymethyl-2-... 

Quinoxaline-2,3-dione is converted into 2,3-dichloroquinoxaline by phosphoryl chloride142 or phosphorus pentachloride.143 2,3-Dibromo-quinoxaline is similarly obtained using phosphoryl bromide in dimethyl-aniline.144 Quinoxalin-2-one undergoes ring contraction to 2-methyl-benzimidazole (134) with hydrazine145 however, quinoxaline-2,3-dione gives 3-hydrazino-2-quinoxalinone.145 Quinoxalin-2-one yields a 3-p-dimethylaminophenyl derivative with 7V,N-dimethylaniline (in AcOH, with NH4N03), and a 3-(indol-3-yl) derivative with indole.146... 

Side hydrazino groups can be effectively removed oxidatively by an appropriate and mild oxidizing agent. For example, copper(II) sulfate oxidizes 5,6,7,8-tetrafluoro-2,3-dihydrazino-quinoxaline to afford 5,6,7,8-tetrafluoroquinoxaline (Table 16).267... 

Syntheses of fused mesoionic heterocycles such as [l,2,3]triazolo[l,5-a]-quinoline, -quinazoline, -quinoxaline, and -benzotriazine derivatives have been described <02T3185>. Cyclizations of alkyl 2-benzoylamino-(4,5-dicyano-1 //-1,2,3-triazol-1 -yl)propenoates gave [1,2,3]triazolo[l, 5-a]pyrazines <02H(56)353>. Reaction of triethyl N-( 1 -ethy 1-2-methy 1-4-nitro-l//-imidazol-5-yl)phosphorimidate with aryl isocyanates provided a route to 2-aryI-2//,4//-imidazo[4,5-fif][l,2,3]triazoles <02JCS(P 1)1968>. 2-(A,A-Diphenylamino)-4-hydrazino-6-... 

Hydrazino-3-methoxyquinoxaline has been hydrolyzed to quinoxaline-2,3-dione by treatment with boiling 48% HBr or 2% HCl at 140-150 . A series of 2-hydrazino-3-alkoxyquinoxalines gives 2-(2-acetylhydrazino)-3-alkoxyquinoxalines by reaction with l-acetyl-3,5-dimethylpyrazole, and benzoylation of the methylhydrazino compound 2 similarly yields the benzoyl derivative 3." ... 

Treatment of the dihydroimidazo[l,2-a]quinoxaline 19 with sodium hydroxide solution results in opening of the five-membered ring and formation of the quinoxalinone 20. The 4-chloro derivative 21 is susceptible to nucleophilic attack, and displacement of the chlorine has been achieved with sodium methoxide, sodium alkoxides in benzene, and hydrazine. The 4-hydrazino derivative was not isolated but was treated with copper sulfate and sodium hydroxide to give the 4-unsubstituted compound. ... 

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