Hydrogenation of quinoxalines

Hydrogenation of quinoxaline, or 1,2,3,4-tetrahydroquinoxaline, over a 5% rhodium-on-alumina catalyst at 100°C and 136 atm, or over... 

Catalytic hydrogenation of quinoxaline derivatives using Raney nickel or rhodium on alumina has been described. 

The catalyst has been used successfully for the complete hydrogenation of quinoxaline and for reduction of the 4,5-double bond of pyrimidine nucleosides and nucleotides. ... 

Reduction of quinoxaline with sodium in THF at 20° yields a deep-purple solution from which 1,4-dihydroquinoxaline is isolated. Reduction with either sodium in refluxing alcohol or lithium aluminum hydride in ether gives 1,2,3,4-tetrahydroquinoxaline. Hydrogenation of quinoxaline over a 5% rhodium-on-alumina catalyst at 100° and 136 atm or over freshly prepared Raney nickel W-6 under similar conditions gives meso-(cis)-decahydroquinoxaline. ° However hydrogenation of quinoxaline over a palladium-on-charcoal catalyst at 180° and 50 atm gives dl-(/rans)-decahydroquinoxaline." ... 

Rapala et al. J Am Chem Soc 79 3770 1957], nicotinic acid to hexahydronicotinic (nipecotinic) acid without decarboxylation [2 atmospheres, 25°, 4 hours Freifelder J Org Chem 27 4046 1962, Freifelder J Org Chem 28 602, 1135 1963], complete hydrogenation of quinoxaline [Broadbent at al. J Am Chem Soc 82 189 1960], reduetion of the 4,5-double bond of pyrimidine nucleosides and nucleotides [Cohn Doherty JAm Chem Soc 78 2863 1956], dehydrogenation e g. hydrogen transfer from hexahydrohexahelicene to benzene in order to provide hexahelieene and cyclohexane in 73% yield [Newman Lednicer J Am Chem Soc 78 4765 1956, cf also Anderson Anderson J Org Chem 22 1197 1957], and hydrogenation of anilines to cyclohexylamine with httle hydrogenolysis [Freifelder et al. J Org Chem 30 2485 1965],... 

The use of air-stable catalyst, a combination of [Cp lrCl2]2 (222) with (223), for selective transfer hydrogenation of quinoxalines in H2O with HC02Na (H2 source) produced corresponding tetrahydroquinoxalines in good to excellent yields. The aqueous phase reduction was highly pH dependent, with acidic pH leading to better results. The HOAc/NaOAc buffer solution was used to maintain the pH of the reaction mixture at which optimum rate was obtained. ... 

Chiral NHC-Ru complexes have been successfully involved in the asymmetric hydrogenation of quinoxalines. Complete conversions have been achieved but ees remained under 90%. 

SCHEME 13.19 Asymmetric homogeneous hydrogenation of quinoxalines catalyzed by ruthenium A-heterocyclic carbene complexes. 

Recently, Chen et al. reported a novel hydrogenation of quinoxalines 357 via the convergent disproportionation reaction of dihydroquinoxalines 359 under a ruthe-nium/Br0nsted acid relay catalysis system (Scheme 2.95) [130a]. This transformation was initiated by the reduction of quinoxalines to dihydroquinoxalines 359 under the catalysis of [Rul/i-cymene) ] 360 the active intermediate then underwent phosphoric acid-catalyzed self-transfer hydrogenation to afford primary starting material 357... 

Fan et al. have successfully developed an efficient metal/ Bronsted acid (261) relay catalysis system for highly enantioselective hydrogenation of quinoxalines (374) through a convergent asymmetric disproportionation of dihydroquinoxalines (375) to chiral tetrahydroquinoxalines (377) with up to 94% ee (Scheme 99). ... 

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