3- -quinoxalinone reduction

A,A-Dibenzyl-2-(ethoxycarbonylmethyl)amino-4-(trifluoromethyl)aniline (27) underwent reductive debenzylation and spontaneous cyclization to 6-trifluoro-methyl-3,4-dihydro-2(17/)-quinoxalinone (28) [Pd(OH)2/C, EtOH, H2 (3 atm), 3 days 97%]. " °... 

Acetamido-5-methoxy-1,2-benzenediamine (prepared in situ by reduction of 1 -acetamido-2-methoxy-4,5-dinotrobenzene) gave 6-acetamido-7-methoxy-quinoxaline (104) (OHCCHO-2NaHS03 H20, 70°C, 2 h 96%). 4-Acetamido-2,3-diaminophenol (105) (prepared in situ by reduction of the 2,3-dinitro analog) gave 8-acetamido-5(l//)-quinoxalinone (106) (OHCCHO-2NaHS03-H20, reflux, Nji, 2 h 79%). °... 

Electrolytic reduction of 5,12-diacetyl-5,12-dihydroquinoxalino[2,3- ]quinoxa-line (593) in H2S04-H20-Me0H afforded 3,4-dihydro-2(l/i)-quinoxalinone (594) in unstated yield a mechanism was suggestedJ ... 

Dimethoxy-1 -methyl-3-p-nitrostyryl-2( l//)-quinoxalinone gave 3-p-amino-phenethyl-6,7-dimethoxy-l-methyl-2(l//)-quinoxalinone (102) (H2, Pt02, AcOEt, 20°C 72% note incidental reduction of the nitro group). 

Note Such deoxygenation is usually accompanied by partial nuclear reduction. 3-phenyl-2(177)-quinoxalinone (90) gave 2-phenyl-3,4-dihydroquinoxaline (91) (LiAlH4, THF, N2, 0°C reflux, 24 h 65%). ... 

Reduction of 2-cyano-3-quinoxalinone 1-oxide with sodium dithionite, zinc and acetic acid, or by catalytic hydrogenation was accompanied by loss of the cyano group, and in each case 2-quinoxalinone was formed.194... 

Diazines other than diketopiperazines can also be prepared on insoluble supports (Table 15.31 see also Figure 3.13 [382]). Most strategies are based on intramolecular nucleophilic substitutions or acylations. Several examples of the solid-phase preparation of quinoxalinones have been reported. In most cases, the compounds have been prepared from support-bound 2-fluoronitrobenzenes according to the strategies outlined in Figure 15.18. Alternatively, a-amino acid esters bound to polystyrene as IV-benzyl derivatives can be N-arylated with 2-fluoronitrobenzene. Reduction of the resulting 2-nitroaniline leads to the formation of quinoxalinones [383]. 1,4-Diazines have been chemically modified by N- or C-alkylation on insoluble supports (Entries 9 and 10, Table 15.31). 

As shown in Scheme 23, solid-phase-bound Fmoc-protected amino acids 82 are deprotected and coupled with 4-fluoro-3-nitrobenzoic acid. The acid moiety of 83 is converted to the amide 84, and reduction of the nitro group with SnCU 2112O initiates cyclative cleavage to 85 after aqueous work-up. This synthesis gives two points of diversification, which can be increased by an alkylation step in solution to give 86. Additionally, the authors oxidized the heterocychc core 85 with p-chloranil to give the corresponding quinoxalinones (not shovm) [38]. 

Tseng and colleagues [58] reported a three-step synthesis of fused tetrahydro-P-carbolinequinoxalinones, solely based on the use of ionic liquids as solvents. Tetrahydro-P-carboline is a central core for many biologically important indole alkaloids, and the moiety of quinoxalinone often exhibits a wide spectrum of biological activities such as being anti-HIV, antihypertensive, and a ligand for a number of protein receptors. As a first step, tryptophan methyl ester was reacted with an aldehyde to form tetrahydro-p-carboline by Pictet-Spengler cyclization that further reacted with l-fluoro-2-nitrobenzene to form iV-aryl-tetrahydro-P-carboline. Intramolecular cyclization upon a reduction reaction in step three provided the desired tetrahydro-P-carbolinequinoxalinones. The entire process was based on the use of 1-n-butyl-... 

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