2- Methylquinoxaline reduction

Catalytic reduction of 2-acetyl-3-methylquinoxaline (29) in ethanol with 1 mole of hydrogen, gives a deep crimson solution, from which red-brown needles of 2-acetyl-l,4-dihydro-3-methylquinoxaline (30) are obtained. Ethanolic solutions of (30) reoxidize on exposure to air to 2-acetyl-3-methylquinoxaline, but the solid dye is stable in air for several days. Similar results are obtained with 2-acetyl-3-phenyl-quinoxaline (31), from the reduction of which a purple-red dye (32) is obtained. ... 

In boiling ethanol, under nitrogen and in the presence of palladized charcoal, 2-acetyl-l,4-dihydro-3-methylquinoxaline (30) undergoes dismutation to give a mixture of 2-acetyl-3-methylquinoxaline, 2-acetyl-l,2,3,4-tetrahydro-3-methylquinoxaline (33), and 2-l -hydroxy-ethyl-3-methylquinoxaline (34), The latter compound is the product of sodium borohydride or Meerwein-Ponndorf reduction of 2-acetyl-3-methylquinoxaline. 

CH2CI2 solution and was reused for several reductions of B. After three reuses, the catalyst maintained its activity, but the enantiopurity of the products decreased by --10%. The complex did not catalyze the reductions of A, C, or 2 methylquinoxaline, and it was inactive in aqueous solution. On the other hand, the catalysts supported on cross linked polystyrenes with hydrophilic SOjNa or amphiphilic... 

W Enantioselective Reduction of Nitrogen Based Heteroaromatic Compounds Table 10.15 Asymmetric hydrogenation of 2 methylquinoxaline. 

Quinoxaline mono-iV-oxides result from the partial reduction of the di-N-oxides. Among reagents that have been used for this purpose are hydrogen and a metal catalyst, phosphorus trichloride, and sodium dithionite. Thus 2-methylquinoxaline 1-oxide has been prepared by partial hydrogenation of the di-JV-oxide quinoxaline-2-carboxyanilide 1-oxide has been prepared from the partial deoxygenation of the 1,4-dioxide with phosphorus trichloride and quinoxaline-2-carboxylic acid... 

A successful preparation of 3-methylquinoxaline-2-carboxaldehyde (9) by the selective reduction of the ester 8 is reported. ... 

Alkylquinoxalines have also been prepared by various transformations of preformed quinoxalines. Thus 2-carboxy groups are usually readily decarboxylated and 2-chloro groups removed by catalytic hydrogenation. Illustrative of this approach is the reduction of 2-chloro-3-methylquinoxaline to 2-methylquinoxaline. " ... 

A systematic study of the electrochemical reduction of 2-methyl-, 2,3-dimethyl-, 2-phenyl-, 2,3-diphenyl-, and 2-methyl-3-phenylquinoxaline in alkaline or neutral media has been made. For example, reduction of 2-methylquinoxaline in either an alkaline or neutral medium gives 1,2-dihydro-3-methylquinoxaline at pH 9 and a higher reduction potential,... 

Reductive elimination. Excess NaBH4 added in small portions to a suspension of cis and rran -S-methyl-l,3-diphenyl-l,3-dihydrothieno[3,4-b]quinoxalinc 2,2-di-oxide in methanol heated on a steam bath 2,3-dibenzyl-5-methylquinoxaline. Y 87%. F. e., also oxidative elimination, s. E. J. Moriconi, T. E. Brady, and R. E. Misner, J. Org. Chem. 36, 479 (1971). 

Reduction of the quinoxalines 5 leads to hydropyrroloquinoxalines 6-8 (Nelson and Boyer 1950 Okumura and Shigemitsu 1965). The pyrrolo[l,2-a]quinoxaline system (compound 6) was first obtained by this method (Okumura and Shigemitsu 1965). During the reductive cyclization of ethyl quinoxalin-2-yl- and 3-methylquinoxalin-2-ylpyruvates 5 in the presence of copper chromite at high temperature, the perhydropyrrolo[l,2-a]quinoxalines 7 and 8 are formed (Scheme 3.2). 

It has been also shown that 3-(P-2-nitrostyryl)quinoxaIin-2-(l//)-ones 141 are easily obtained from 3-methylquinoxalin-2(lfl)-one 52 and o-nitrobenzaldehyde 126, and when exposed to sodium dithionite are converted into 2-(benzimidazol-2-yl) quinolines 142 (Mamedov et al. 2010c). The process occurs under reduction conditions in a cascade of the modified Friedlander reaction and the new acid-catalyzed rearrangement through the intermediately formed products-3-(P-2-aminostyryl) quinoxalin-2(lfl)-ones 143 (Scheme 6.60). 

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