Quinoxaline, reductive acetylation

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. ... 

Quinoxaline gave l,4-diethyl-l,2,3,4-tetrahydroquinoxaline by indirect reductive alkylation (AcOH, KBHai, <15°C, 1 h, then reflux, 6h 87% presumably by nuclear reduction, A-acylation, and further reduction of the acetyl groups ). ... 

Brightener structures of only moderate molecular size are of interest for white grounds in the transfer printing of polyester fabrics. Derivatives of 6-acetamidoquinoxaline with an electron-donating substituent (X) in the 2-position (11.48) were prepared by converting quinoxalin-2-one to 2-chloro-6-nitroquinoxaline and condensation with amines (X = RNH), alcohols (X = RO) or phenols (X = PhO), followed by reduction and acetylation (Scheme 11.19). The nitro intermediates (11.49) are also of interest as low-energy disperse dyes for polyester [61]. 

Catalytic reduction of 2-acetyl-3-methyl(or 3-phenyl)quinoxaline with 5% palladium on activated charcoal in ethanol gives 2-acetyl-3-methyl(or 3-phenyl)-l,4-dihydroquinoxaline. °... 

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