(4aR*,8aS*)-2,3-Diphenyl-4a,5,6,7,8,8a-hexahydroquinoxaline

In the title compound, C20H20N2, the quinoxaline ring adopts a very distorted half-chair conformation [N=C—C=N = 22.7 (2)° for the nominally coplanar atoms] and the cyclohexane ring adopts a chair conformation. The quinoxaline and cyclohexane rings are cis-fused. The two phenyl rings form a dihedral angle of 63.88 (7)°.

In the title compound, C 20 H 20 N 2 , the quinoxaline ring adopts a very distorted half-chair conformation [N C-C N = 22.7 (2) for the nominally coplanar atoms] and the cyclohexane ring adopts a chair conformation. The quinoxaline and cyclohexane rings are cis-fused. The two phenyl rings form a dihedral angle of 63.88 (7) .

Comment
Dihydropyrazine ring systems are found as a key unit in natural products and biochemical materials (Raw et al., 2003).
Therefore, the synthesis of dihydropyrazine derivatives attract much interest in organic chemistry. In this respect, we report herein the crystal structure of the title compound.
In the title compound, Fig. 1, the quinoxaline ring has a very distorted half-chair conformation and the cyclohexane ring has a chair conformation. The dihedral angle between the two benzene rings is 63.88 (7)°. The lengths of the C═N bonds [1.2678 (18)Å] are comparable to those in similar compounds (Wang et al., 2008;Reich et al., 2004).
The compound was recrystallized from methanol to give yellow blocks.

Refinement
Hydrogen atoms were positioned geometrically and allowed to ride on their parent atoms, with C-H = 0.93-0.98 Å, and with U iso (H) values set to 1.2U eq (C).  The molecular structure of the title compound with displacement ellipsoids drawn at the 30% probability level.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.