1,2,3,4-Tetrahydroquinoxaline alkylation

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 ). ... 

The method has also been applied to the synthesis of alkyl-substituted quinoxalin-2-amines. Thermal rearrangement of l-(2-aminophenyl)-4,5-dihydro-5-morpholino-l,2,3-triazoles 15 affords unstable 2-alkyl-l,2,3,4-tetrahydroquinoxalin-3-amines, which undergo deamination and consequent oxidation to afford 2-alkylquinoxalines 16. ... 

Quinoxaline is reductively alkylated with potassium borohydride in acetic acid to yield 1,4-di-ethyl-1,2,3,4-tetrahydroquinoxaline in 87% yield. ... 

As mentioned above, Vitzthum and Werkhoff (1975) reported for the first time 17 alkylated five-and six-membered bicyclic pyrazines in roasted coffee The tetrahydroquinoxalines reference standards were synthesized according to the IFF British Patient 1 310771. The mass spectra of these new constituents are discussed and fragmentation pathways for 2-ethyl-5,6,7,8-tetrahydroquinoxaline 0.69 and 2,3-dimethyl-5,6,7,8-tetrahydroquinoxaline 0.70 are commented upon in detail. 

Morpholinocyclohexene has been used as starting material for the synthesis of l-alkyl-2-amino-l,5,6,7-tetrahydroquinoxaline 3-carboxyl-ates (31) as shown in Scheme 5. ... 

Alkylation of tetrahydroquinoxalines cannot be stopped at the monoalkylation stage however treatment of tetrahydroquinoxalines with ben-zenesulfonyl chloride, at a low temperature, gives monophenylsulfonyl derivatives. These on alkylation and subsequent acid hydrolysis of the protecting group yield l-alkyl-l,2,3,4-tetrahydroquinoxalines. " An alternative approach involves the alkylation of tetrahydroquinoxalin-2-ones and subsequent reductive removal of the carbonyl function (Scheme... 

The best method for preparing 1-methyl- and 1-ethyltetrahydroquin-oxaline (35) is by the sodium borohydride reduction of methylquinoxa-linium p-toluenesulfonate (33) or ethylquinoxalinium iodide (34), respectively. Further alkylation of l-methyl-l,2,3,4-tetrahydroquinoxaline... 

Substituted tetrahydroquinoxalin-2-ones have been prepared on the RAM support 7c [303] by first coupling 4-fluoro-3-nitrobenzoic acid to the support in the presence of HATU using a procedure comparable to that described earlier followed by displacement of fluorine by an a-aminoester. Reduction of the nitro group useing tin (II) chloride lead to ring closure (Scheme 13) and further alkylation was followed by TFA-induced cleavage. 

Related heteroannulation chemistry has been conducted on the solid-phase and provided new routes to hydrobenzofu-rans, hydrobenzopyrans, indolines and tetrahydroquinolines. Using alkenyl-based substrates in solution-phase variations of such processes has led to ( -2-alkyl(aryl)idene-l,2,3,4-tetrahydroquinoxalines and pyrido[2,3-4]p3Timidines. ... 

Alkylation of o-(A-sulfonylamino)phenyimino derivatives of indol-2-one and cyclohepta[c]furan 211 with phenacyl bromides 212 is accompanied by cyclization to tetrahydroquinoxalines 213 with spiro-fused oxoindole or cyclohepta[c]furan fragments (Scheme 2.16) (Kurbatov et al. 2004). In these cases, only one carbon atom is supplied by the phenacyl bromides for the construction of the pyrazine. 

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