Quinoxalines 1,2,3,4-tetrahydro- from

Except for the tetrahydrobiaryls derived from acridine and from quinoxaline, the postulated intermediate tetrahydrobipyridines have not been isolated but such compounds may be too unstable under the conditions of the reaction to permit their isolation. Evidence is, therefore, still lacking for the last two steps of dehydrogenation and desorption from the catalyst. Dehydrogenation could conceivably occur while the tetrahydro derivative is still adsorbed on the catalyst,... 

This method is widely applicable to the unambiguous synthesis of quinoxalin-2-ones." It involves the intermediate preparation of a l,2,3,4-tetrahydro-2-oxoquinoxaline by the reductive ring closure of the o-nitrophenyl derivative of an a-aminoacid. These derivatives are formed readily from the aminoacid and an o-nitrohalogenobenzene. The final step of oxidation of the tetrahydro- to the dihydro-quinoxa-line is carried out with potassium permanganate or hydrogen peroxide. The preparation of 7-nitroquinoxalin-2-one illustrates the application of this synthesis ... 

The cycloaddition reaction (333)+ (334) — (335) illustrates the preparation of tetrahydro-quinoxalines from o-benzoquinone diimines. 

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). 

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-... 

From A. A -diaroyldiimines the [4 + 2] cycloadducts, i.e.. tetrahydro-1//-cyclopenta[b]-quinoxalines 11, are isolated in good yield5,9. The presence of different substituents at C-6 in the fulvene leads to a mixture of two regioisomers9. 

Sodium borohydride or sodium borohydride and trifluoroacetic acid reduce 5- or 6-sub-stituted quinoxalines to the 1,2,3,4-tetrahydro compounds 1.2,3,4-tetrahydroquinoxaline is also formed in the reduction of quinoxaline with bis(trifluoroacetoxy)boranc-tetrahydrofuran. The sodium borohydride reduction of 2,3-dimethylquinoxaline 1,4-dioxide in alcohols affords c 3-2,3-dimethyl-l,2,3,4-tetrahydroquinoxaline as the predominant product and identical to that obtained from the reduction of 2,3-dimethylquinoxaline with lithium aluminum hydride. ... 

Alkylquinoxalines have been prepared from o-phenylenediamines and a-haloketones, for example, reaction of o-phenylenediamine with 3-chlorolevulinic acid ethyl ester (5) gives the quinoxaline 6. ° An analogous reaction between the bromoketone 7 and o-phenylenediamine gives a mixture of 2-(-butylquinoxaline (8) and 2-t-butyl-l,2,3,4-tetrahydro-quinoxaline (9). However, when the dibromoketone (CHBr2COCMe3) is used, only 2-f-butylquinoxaline is obtained. ... 

Tetrahydroquinoxalines have also been prepared by cyclization of ortho-disubstituted benzenes. Thus high-temperature (200-210°) reaction of catechol with ethylenediamine gives 1,2,3,4-tetrahydro-quinoxaline tetrahydroquinoxalines have also been prepared from hexafluorobenzene. ° The reaction of N,N -ditosyl-o-phenylenediamine with a variety of 1,2-dibromo compounds " gives. 1,2,3,4-tetrahydro-quinoxalines, as illustrated in Scheme 3. 

Two papers described novel general conversions of diamines into piperazines. Taylor et al ° reacted phenylene diamines with a-epoxy nitriles or sulphones to synthesize tetrahydro-quinoxalines in yields of between 30 and 90%, and Lai reported an interesting preparation of the l,3,3,5,5-pentasubstituted-2-piperazinones (340) and (341) from ethylene diamines (339) via a phase-transfer-catalysed reaction with ketones and chloroform this latter was... 

An alternative method to prepare hexahydrocohulupone from hexahydrocolupulone involves reduction of 4-hydroperoxyhexahydrocolupulone to 4-hydroxyhexahydrocolupulone (208, Fig. 87) (see 13.1.2.) (2,17,24,25). In alkaline conditions this alcohol rearranges to 5-(3-methylbutyl)tetrahydro-isocohumulone (209, Fig. 87). Further hydrolysis leads to 5-(3-methylbutyl)dihydrocohumulinic acid (210, Fig. 87). This hexahydroderivative of cohulupone (see 13.1.1.2.3.) can be oxidized to tetrahydrocohulupone (206, Fig. 87) by oxidation with bismuth(lll) oxide. The compound is characterized as the sodium salt (melting point 228°C) and the quinoxaline involving 1,2-diaminobenzene (melting point 150°C). Upon oxidation bis(3-methylbutyl)malonic acid and 2-methylpropanoic acid are formed (17). This reaction sequence via the hydrogenated derivatives provides chemical proof for the structure of the hulupones. 

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