Pyrido quinoxaline preparation

Quinoxalines have been prepared starting from common 1,2-diketones and 1,2-aryldiamines in MeOH/AcOH at 160 °C for 5 min under microwave irradiation (Scheme 81). Several differently substituted quinoxalines 223 and pyrido[2,3-b]pyrazines were prepared with this method, which Umitation may be the symmetry of the diketone 221 or the diamine 222 employed, in order to avoid the formation of a mixture of regioisomers [142],... 

That of 1,4-dichlorobutane and quinoxaline sodium salt 408, prepared from quinoxaline with metal Na in THF, provided 7,8,9,10-tetrahydro-6flH-pyrido[l,2-fl]quinoxaline 409 (08M669). 

Lindsley and co-workers developed a general procedure towards the collection of diverse heterocyclic scaffolds from common 1,2-diketone intermediates 96. Substituted quinoxalines 97, fused pyrazolo [ 4,5-g ] quinoxalines 98 and imidazolo[3,4-g]quinoxalines 99 as well as pyrido[2,3-fo]pyrazines 100 and Ihicno[3,4-fo Ipyrazincs 101 have been prepared in excellent yields [132] (Scheme 54), employing optimized reaction conditions (microwave heating of equimolar mixtures of 1,2-diketone 96 and diamine components at 160 °C for 5 min in 9 1 MeOH - AcOH). The use of microwave irradiation resulted in reduced reaction times (5 min vs. 2-12 hours), improved yields as well as the suppressed formation of polymeric species a characteristic of traditional... 

Benzylperhydropyrido[l,2-a]pyrazin-6-one was prepared through the cyclization of 287, obtained from 285 via 286 (93JOC690). From the reaction mixture of 2,3-di(2-tetrahydrofuryl)piperazine, treated with HBr gas in AcOH at 90-95°C, then with KOH, l-(2-tetrahydrofuryl)-9-hydroxy-perhydropyrido[l,2-a]pyrazine could be isolated (61BSF2135). Cyclization of 2-(l,2,3,4-tetrahydroxylbutyl)quinoxalines in an acidic media gave 8H-pyrido[l,2-a]quinoxalin-8-ones together with a small amount of their 9-... 

Isomerization of benzo[/]-l,5-diazabicyclo[3,2,2]nonene in 8.8 N HBr at 140°C yielded l,2,3,5,6,7-hexahydropyrido[l,2,3-de]quinoxaline (83 KGS677). Photolysis of dimethyl l-(quinolin-8-yl)-l,2,3-triazole-4,5-di-carboxylates in MeCN resulted in stable an/tydro-2,3-dimethoxycarbonyl-3//-pyrido[l,2,3-de]quinoxalin-4-ium hydroxides [87JCS(P1)403]. 6-Hy-droxymethyl-2-methyl-7-methoxy-l,2,3,4-tetrahydro-6//-pyrazino-[1,2-h]isoquinolin-4-one (138) was prepared from 5- [A-methyl-Ar-(ethoxy-... 

The X-ray crystal structures of pyrazine V.JV -dioxide (134) <02AX(E)1253>, the P-polymorph of phenazine (135) <02AX(C)181>, cobalt(III) complexes of pyrazine-2,6- and pyridine-2,6-dicarboxylic acids <02JIC458>, and bis-urea-substituted phenazines <02ZN(B)937> were reported. Fluorescent pyrido[l,2-a]quinoxalines 136 prepared as pH indicators were examined by X-ray crystallography <02JCS(P2)181>, as were macrocyclic quinoxaline-bridged porphyrinoids obtained from the condensation of dipyrrolylquinoxalines 137 and 1,8-diaminoanthracene... 

Nitrogen Heterocycles.- Reactions of iminophosphoranes have been used to prepare a wide range of heterocycles. Examples of compounds prepared by intramolecular aza-Wittig reactions include 3,4-dihydroquinazolines (191) and quinazolines (192), quinazoline derivatives (e.g. 193),pyrrolo( 1,2-a)quinoxalines (194), indolo[3,2-clquinolines (195), and indolo[l,2-c]quinazolines (196),"8 imidazolinones (197),"9 quinazolinones (198),"9, 120 pyrido[2,3-d]pyrimidine derivatives (199), 21 and 4,5-dihydropyrazolo(3,4-d]pyrimidine derivatives (200). 22 Tributyl(cyclohepta-1,3,5-trienylimino)phosphorane (201), prepared by thermal isomerization of the 2,4,6-derivative, reacts with a,p-unsaturated ketones to give 9H-cyclohepta[b]pyridine derivatives (202). 23 a synthesis of (2,4)pyridinophanes (204) by the reaction of N-vinyliminophosphoranes (203) with a,P-unsaturated ketones has been reported. 24... 

The pyrazine ring is stable to permanganate oxidation, and this accounts for a variety of pyrazinecarboxylic acids that have been prepared from quinoxalines, benzo-fused quinoxalines including phenazines, and pyrido-fused pyrazines . In other fused systems, particularly pter-idines, the pyrimidine ring is easily hydrolyzed under either acidic or basic conditions to give numerous 3-aminopyrazinecarboxylic acid derivatives. 

A series of complex derivatives (18) of the ring system have been prepared by reaction of the pyranylidene compounds 17 with o-phenylenediamine." The only other pyrido[l,2-a]quinoxaline to be reported is compound 19, obtained from the reaction of quinoxaline with two molecular equivalents of dimethyl acetylenedicarboxylate. ... 

Darabi et al. introduced a different, facile, and economic approach to the preparation of quinoxalines and pyrido[2,3-l)]pyrazines with aryl substituents at the 2- and/or 3-positions by employing recyclable sihca-supported bismuth(III) chloride, providing the desired products in good-to-excellent yields (Scheme 59) (13JOMC170). A minor decrease in the activity of this new heterogeneous Lewis acid catalyst upon repeated usage was noted. A variety of substituents were tolerated under these reaction conditions. 

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