1.2.3.4- Tetrahydro-2-methylquinoxaline

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. 

Bromomethyl-2,3-dimethoxy-7-methylquinoxaline (265) underwent a classical Sommelet reaction and incidental hydrolysis of the methoxy groups to give 7-methyl-2,3-dioxo-l,2,3,4-tetrahydro-6-quinoxalinecarbaldehyde (266) (hexamethylenetetramine, CHCI3, 20°C reflux, 30 min solid from evapora-... 

Quinoxaline170-172 is reduced to 1,4-dihydroquinoxaline (167) in a reversible reaction. 2-Methylquinoxaline is reduced to 3,4-dihydro-2-methylquinoxaline (168),172 whereas 2-phenylquinoxaline forms l,2-dihydro-2-phenylquinoxaline (169) the 1,4-dihydroquinoxalines may be formed primarily, but are then tautomerized to the more stable dihydroquinoxaline. 2,3-Diphenylquinoxaline is reduced to as-l,2,3,4-tetrahydro-2,3-diphenylquinoxaline, the 1,4-dihydro compound is transformed into the 1,2-dihydro derivative, which is further reducible.172... 

Scheme 2.125 The synthesis of l,2,3,4-tetrahydro-4-methylquinoxaline-2-spiro-5 -(hexahydro-2, 4, 6 -trioxopyrimidine 531...

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