2-Phenyl-5,6,7,8-tetrahydroquinoxaline

Diphenyl-5a,6,7,8,9,9a-hexahydro- 17/-benzodiazepine (448) underwent vapor-phase pyrolysis ( 750°C but no further details) to give 2-phenyl-5,6,7,8-tetrahydroquinoxaline (449) (46%) and 2,4-diphenyl-5,6,7,8-tetrahy-droquinoxaline (450) (4%). ... 

Dibenzyl-2,2-dimethyl-2,3-dihydrobenzimidazole (429) gave 1,4-dibenzyl-2,2-dimethyl-3-phenyl-l,2,3,4-tetrahydroquinoxaline (430) (neat, 200°C, sealed, h 11% after separation from benzaldehyde mechanism pro-... 

Methylquinoxaline with phenyUithium gave a separable mixture of 2-methyl-3-phenylquinoxaline (45), 2-methyl-3-phenyl-3,4-dihydroquinoxaline (46), and 2-methyl-2,3-diphenyl-1,2,3,4-tetrahydroquinoxaline (47) [PhLi (made in situ), Et20, <20°C, 90 min 20%, 45%, and 35%, respectively). 

Methyl-1,2,3,4-tetrahydroquinoxaline (161) gave 1-methyl-4-[A -phenyl(thio-carbamoyl)]-l,2,3,4-tetrahydroquinoxaline (162) (PhNCS, CH2CI2, reflux, 1 h 30%). ... 

An ( )-TolBINAP-Ir complex with a protic amine such as benzylzmine as the additive has been applied for the hydrogenation of 2-phenyl-3,4,5,6-tetrahydropyridine, and enantioselectivity up to 90% ee is obtained.314 An ortho-metallated Ir dihydrid complex has been used in the hydrogenation of 2-methylquinoxaline, and enantiopurity up to 90% ee has been obtained for the 2-methyl-1,2,3,4-tetrahydroquinoxaline product (Scheme 16).327... 

The reaction of or//io-substituted anilines containing substituent groups, e.g., phenyl, cyano, and nitro, gives rise to simple enamine fumarates these in turn can be cyclized to the corresponding 4-quinolones. " Aromatic diamines such as o-phenylenediamine and 2,3-diaminonaphthalene, however, react with DMAD to give tetra-hydroquinoxaline derivatives (7) [Eq. (2)]. ° It has been suggested that these tetrahydroquinoxalines exist in tautomeric equilibrium between the imine and enamine forms and that the enamine form (7) is more favored in inert organic solvents. On the other hand, an iso-... 

The reaction of iV-phenyl-o-phenylenediamine (10) with DMAD gives a mixture of products consisting of l-phenyl-2-oxo-3-carbomethoxy-methylene-l,2,3,4-tetrahydroquinoxaline (11) and l-phenyl-2,3-dicarbo-methoxy-l,2,3,4-tetrahydroquinoxaline (12) [Eq. (4)]. m-Phenylene-diamine and p-phenylenediamine give the corresponding bisenamines 13... 

A mixture of 7-chloro-4-hydroxy-1-methyl-5-phenyl-2,3,4,5-tetrahydro-lH-1,4-benzodiazepine, SOCI2, and methylene dhloride stirred 15 min. at room temp. -> crude 6-chloro-l-methyl-l,2,3,4-tetrahydroquinoxaline. Y 63%. F. e., also with POCI3 and limitations, s. A. Walser et al., J. Org. Chem. 36, 1248 (1971). 

Scheme 2.89 The rearrangement of 2,2-dialkyl-l,3-dibenzyl-2,3-dihydrobenzimidazoles 447 to the isomeric l-benzyl-3,3-dialkyl-2-phenyl-l,2,3,4-tetrahydroquinoxalines 448...

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