3-aroyl-2- quinoxalins

Thermolysis of 3-alkyloxy- and 3-aroyloxy-5-phenyl-l,2,4-pyrrolo[l,2- ]quinoxaline-l,2,4-triones afforded 5-phenyl-9-(4-phenyl-3-oxo-3,4-dihydro-2-quinoxalinyl)-6,8,10-trioxo-5,6,9,10-tetrahydro-87/-pyrido[l,2-tf ]quinoxaline-7,9-dicarboxylates <2000CHE615, 2004CHE1295> and 7-aroyl-8-aroyloxy-5-phenyl-9-(4-phenyl-3-oxo-3,4-dihydro-2-quinoxalinyl)-5,6-dihydro-1077-pyrido[l,2- ]quinoxaline-6,10-diones <2002CHE498>, respectively. Thermolysis of 3-aryl-2-(5-aryl-2,3-dioxo-2,3-dioxo-4-furanyl)quinoxalines gave 7-aroyl-8-aroyloxy-6-aryl-9-(3-aryl-2-quinoxalyl)-10/7-pyrido[l,2- ]quinoxalin-10-ones <2001CHE1314, 2002RCB850>. 

Bakavoli et al. have synthesized new 3-substituted [l,2,4]triazolo[3, 4 2,3][l,3]triazolo[4,5- ]quinoxalines by the cyclocondensation of [l,3]thiazolo[4,5- ]quinoxaline-2(3//)-one hydrazone with aroyl chlorides, trimethylorthofor-mate, or triethylorthoacetate H NMR data are provided <2006PS(111)99>. 

Upon thermolysis 5-aryl-4-quinoxalinyl-2,3-dihydro-2,3-furandiones [3-aryl-2-(2-aryl-4,5-dioxo-4,5-dihydro-3-furyl)quinoxalines] 223 leads to decarbonylation and formation of 3-aryl-2-quinoxalinyl(aroyl)ketenes 224, which can be captured using cychc ketones such as cyclopentanone... 

In a similar manner, imidoylketenes 320, created from 3-aroyl-5-phenyl-l,2,4,5tetrahydropyrrolo[l,2-a]quinoxaline-l,2,4-triones 319, are subjected to cyclo-dimerizations to afford the cyclodimers 321 in 68—72% yields (Scheme 101) (2005RJOC1081). When R = 2-(5-methyffuranyl), the yield of the cyclodimer is good (2002CHE498). Likewise, cyclodimerization is reahzed in the creation of 320 (R = OEt) however, the yield of the cyclodimer is poor (2000CHE615). Even, lower yields of the cyclodimers are obtained upon the thermolysis of the ester-substituted trione (COOR) (2004CHE1295). 

A facile iodine / water-mediated oxidation of the triple bond of o-alkynylaroyl compounds to furnish tricaiboityl compounds has been reported by Sakthivel and Srini-vasan (Scheme 8.14) [16]. The reaction proceeds through the formation of isochro-menol intermediates by the assistance of the neighboring aroyl group. The product tricarbonyl compounds were versatile synthetic precursors that, upon treatment with mono and diamines, hydrazines, and aminoalcohols, afford various heterocyclic scaffolds such as isoindolinones, phthalazines, benzimidazoisoquinolinones, quinoxalines, and benzimidazole-quinoxaline hybrid compounds. 

Unsymmetrical benzils, Ar -COCO-Ar, have been prepared via NHC-catalysed nucleophilic aroylation of A-phenylimidoyl chlorides, Ar -C(C1)=N-Ph, by aromatic aldehydes (Ar -CHO), to give the imine, Ari-C(=NPh)-CO-Ar, followed by hydrolysis. Conveniently done in one pot with sodium hydride in refluxing THF, the further in situ conversion of the benzils into 2,3-diaryl-quinoxalines and -pyrazines has been achieved by double-condensation with 1,2-diamines. 

Scheme 2.78 Synthesis of 3-trifluoromethyl/alkoxy/alkyl/alkyloxycarbonyl/and 2-benzoyl/aroyl/ alkanoyl/hetaroyl-quinoxaline 1,4-dioxide derivatives 422...

In a number of cases, the reaction of the quinoxalines 62 with oxalyl chloride with boiling in anhydrous chloroform at 60-63 °C for 2-2.5 h leads to the formation of 3-aroyl- and heteroyl-l,2,4,5-tetrahydropyrrolo[l,2-a]quinoxaline-l,2,4-triones 63 with sometimes almost quantitative yields (Scheme 3.19) (Andreichikov 1994 Tolmacheva et al. 2002 Maslivets et al. 2002 Bozdyreva et al. 2005). 

Bozdyreva KS, Smirnova IV, Maslivets AN (2005) Five-membered 2,3-dioxo heterocycles L. S3mthesis and thermolysis of 3-aroyl- and 3-hetaroyl-5-phenyl-l,2,4,5-tetrahydropyrrolo[l,2-a] quinoxalin-1,2,4-triones. Russ. J Org Chem 41(7) 1081-1088. doi 10.1007/sl 1178-005-0296-6... 

In the reactions discussed above aroyl- and alkanoylquinoxalinones were dealt with as heteroanalogues of a-diketones. Following this line of thought, assume the 3-(a-haloalkyl)- and 3-(a-halobenzyl)quinoxalin-2(l//)-ones, 3-(a-aminobenzyl) quinoxalin-2(lfl)-ones and 3-arylacylidene-3,4-dihydroquinoxalin-2(l//)-ones to be analogues of a-haloketones, a-aminoketones and P-diketones, respectively. 

E) The understanding of the reaction mechanism makes it possible for them to make a bold assumption. As can be seen from Fig. 6.3, all the reactions of aroyl- and alkanoylquinoxalines when interacting with 1,2-DABs at the initial stage behave as hetero analogues of a-diketones, that is, as iminoketones (see Sects. 6.4 and 6.10). Then there arises the problem, why other quinoxaline derivatives with certain substituents do not behave like a-haloketones 49 (see Sect. 6.5), P-diketones 50 (see Sect. 6.6), a-aminoketones 51 (see Sect. 6.7), methyl ketones 52 (see Sect. 6.8), aromatic o-aminoaldehydes (or ketones) 53 (see Sect. 6.9), etc. 

The reaction of quinoxalin-2-one 37a (the schematical presentation of the 3-aroyl-, 3-alkanoyl- and 3-hetaroylquinoxalin-2(l//)-ones as analogues of a-diketones has been shown in Sect. 6.2.3(E) (see Fig. 6.3, structure 37)) with 1,2-DAB 5a in boiling acetic acid leads to the corresponding 2-benzimidazolylquinoxaline 40a in a 97 % yield (Scheme 6.29) (Kalinin 2000 Kalinin et al. 2000). 

This is due to the fact that the probability of an initial attack of the amino group on the C(3) atom of the quinoxalin-2(lfl)-one system and on the aroyl- or alkanoyl group during the rearrangement is approximately the same (Table 6.1) (Kalinin et al. 2000, 2007 Mamedov et al. 2004, 2008a, 2010a). 

It is worthy of note that the products of the reaction of 3-aroyl(alkanoyl) quinoxalin-2(lfl)-ones 37a-e, g, i, t, u and A -alkyl-3-BQs 37o, v, w with diaminomaleonitrile 121 in DMSO-Jg exist solely in spiro-cyclic-forms 123a-l, whereas in the crystalline state they exist only as open chain forms 123 a-I (Mamedov et al. 2012). 

NHC has also been used successfully for the construction of quinoxaline framework in one pot (Scheme 60). The synthesis of 2,3-diarylquinoxalines by the aroylation of N-phenylbenzimidoyl chlorides wi aromahc aldehydes and diamines catalyzed by 3mol% of 1,3-dimethylimidazolium iodide (NHC precursor) has been described by Suzuki et al. [85]. The substrates of the catalytic reaction, i.e., N-phenylbenzimidoyl chlorides, are easily obtained... 

---