Quinoxalines, methyl-, condensations

Condensation of o-phenylenediamine or xV-methyl-o-phenylcne-diamine with alloxan (8) in neutral solution gives the ureides (9) and (10), respectively However, reaction of o-phenylenediamine with 1,3-dimethylalloxan (13) yields quinoxalin-3-one-2-carboxymethyl-amide (14), rather than the dimethyl ureide. Methylation of (9) in acetone in the presence of potassium carbonate gives the spiro-hydantoin (11). 

N-Substituted quinoxalines are obtained from N-substituted o-phenylenediamines. Thus methyl 2,3-dibromopropionate condenses with (V,A -bis(/7-toluenesulfonyl)-o-phenylenediamine to give l,4-bis(p-tolu-enesulfonyl)-2-methoxycarbonyl-1,2,3,4-tetrahydroquinoxaline (20).25 AVV -Disubstituted cyclohexane-1,2-diamines with suitable a/7-dihalides yield decahydroquinoxalines.26 Condensation of cyclohexane- 1,2-diones with glycine amide gives 2-oxo-5,6,7,8-tetrahydroquinoxalines.27... 

In the case of quinazolines and quinoxalines, both /7-tolyl groups and also methyl groups attached to the condensed benzene ring have been found to react with benzalaniline.11 For example, 2-(/>-tolyl)-4-phenyl-6-methylquinazoline (199) gives, with benzalaniline, 2-(stilben-4-yl)-4-... 

Dimethylquinoxaline 1.4-dioxide (1) condenses with diketones to yield a mixture of mono- and di-A-oxides, e.g. diphenyl diketone (2) gives mono- 3 and di-A-oxidcs 4 in 6 and 14% yield, respectively. Since the A-oxide functions of quinoxaline di-A -oxides may be regarded as the combination of two nitrone groups, methyl protons at positions C2 and C3 show enhanced acidity. 

The synthesis of benzothiazolo pyrimidinone 55 involves a regioselective [4+2] cycloaddition of benzothiazolo fused l,3-diazabuta-l,3-diene 53 with phenylketene <04T4315>. Diene 53 is readily prepared from the condensation of 1,3-diazabuta-1,3-diene with 2-aminothiophenol. Condensation of the stable Hantzsch reaction intermediate 56 with 1,2-phenylenediamine 57 in refluxing acetic acid furnishes thiazolo[3,4-a]quinoxalin-4-one 59 <04H(63)1783>. Intermediate 56 is available from the Hantzsch reaction of methyl phenylchloropyruvate with N, -diphenylthiourea. 

A comparative study has been made of the reactivity of the methyl group of a number of 2-raethylbenzodiazines. This has shown that the methyl group in a methylquinoxalinone such as 3-methylbenzo[f]-quinoxalin-2-one (30) is readily condensed with benzaldehydes, furfural, and chloral to give compounds of type 31. The condensation of... 

Hexane-1,3,4,6-tetraones 207, easily available from the double Claisen condensation of methyl ketones and diethyl oxalate (MeONa in ether) (Waring et al. 2002), react with 1,2-DABs 155a, n and (1 ,1 )-1,2-DACH 171b in refluxing EtOH in the same way as a-diketones, resulting in symmetrically substituted quinoxalines 208, 209 and a dissymmetrically substituted quinoxaline 210, all bearing two ketonic arms (Scheme 2.15) (Waring et al. 2002). 

However, the reaction of 2,3-dimethylquinoxaline 51a with maleic anhydride 46a under standard conditions (Taylor and Hand 1963) takes place with the formation of a compound with the empirical formula C14H12N2O3, the IR spectrum of which does not contain bands for the stretching vibrations of the anhydride groups but there are bands for the stretching vibrations characteristic of NH, the OH of the carboxyl function, the double bond, and an amide vinylog (Scheme 3.16). The NMR spectra and the chemical properties of the adduct show that pyrrolo[l,2-a]quinoxaline 52a is formed as a result of the reaction, and this can be represented by the Scheme 3.16 (Taylor and Hand 1962, 1963). Accordingly, the condensation of maleic anhydride with 2-methylquinoxaline and 2-methyl-3-phenylquinoxaline gives 2-carboxymethyl- 52b and 2-carboxymethyl-4-phenylpyrrolo[l,2-a] quinoxalin-l(5H)-ones 52c (Taylor and Hand 1963 Taylor and Cheeseman 1964). 

Mamedov VA, Kalinin AA (2010) Pytrolo[l,2-a]quinoxalines based on quinoxalines. Chem Heterocycl Compd 46(6) 641-664. doi 10.1007/sl0593-010-0565-3 Mamedov VA, Nuretdinov lA (1992) Reaction of methyl dichloroacetate with substituted benzaldehydes under the conditions of the Datzens condensation. Bull Rus Acad Sci Div Chem Sci 41(9) 1690-1692. doi 10.1007/BF00863594... 

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