(3aR,6aR)-1-Phenyl-5-[(R)-1-phenylethyl]-3-[4-(trifluoromethyl)phenyl]-1,6a-dihydropyrrolo[3,4-c]pyrazole-4,6(3aH,5H)-dione

In the title molecule, C26H20F3N3O2, the two central five-membered rings form a dihedral angle of 62.94 (8)°. The absolute configuration was determined by analysis of Bijvoet pairs based on resonant scattering of light atoms, yielding a Hooft parameter y = −0.05 (11). Notable intra- and intermolecular contacts include C—H⋯O and C—H⋯π(arene) hydrogen bonds.

In the title molecule, C 26 H 20 F 3 N 3 O 2 , the two central fivemembered rings form a dihedral angle of 62.94 (8) . The absolute configuration was determined by analysis of Bijvoet pairs based on resonant scattering of light atoms, yielding a Hooft parameter y = À0.05 (11). Notable intra-and intermolecular contacts include C-HÁ Á ÁO and C-HÁ Á Á(arene) hydrogen bonds.
The two 5-membered rings at the core of this molecule are essentially planar and form a dihedral angle of 62.94 (8)°. The mean deviation of the seven pyrrolidine-2,5-dione atoms from their least-squares plane is 0.021 Å, and the mean deviation for the 4,5-dihydro-1H-pyrazole ring is 0.013 Å. Atom N2 deviates most from the 4,5-dihydro-1H-pyrazole ring, with deviation 0.0198 (17) Å. Atom N1 deviates most from the pyrrolidine-2,5-dione ring, with deviation 0.0610 (19) Å. The core of this structure is nearly identical to that found in a recently-reported compound produced in a similar reaction (Fronczek et al., 2009), except that it was the diastereomer with N2 and C5 swapped, and p-acetate substituent on phenyl rather than CF 3 . That compound had dihedral angle between the two 5-membered rings 63.66 (4)°. Similar results can also be found in compounds having refcodes CIRFEP and WIQBIH from the Cambridge Structural Database (Allen, 2002, version 5.30, Nov. 2008. In CIRFEP (Hursthouse et al., 2003), the dihedral angle between the central ring planes is 63.65 (9)°, for one of two independent molecules and 64.23 (9)° for the other. For WIQBIH, (Skof et al., 1998), the dihedral angle formed by the central ring planes 65.99 (6)°. Notable intra and intermolecular contacts include C-H···O and C-H···π(arene) hydrogen bonds, Table 1.
The absolute configuration, based on resonant scattering of the light atoms, was slightly ambiguous from of the Flack (1983) parameter, x = -0.2 (2). Analysis of the Bijvoet pairs using the method of Hooft et al. (2008) yielded a more decisive y = -0.10 (7), corresponding to a probability P2(true) = 1.000 for this structure, confirming the absolute configuration. It agrees with that of the starting materials.
Experimental C-(4-Trifluoromethyl)-N-phenyl hydrazonyl chloride 1 (0,149 g, 0.5 mmol) and (R)-N-(1-phenylethyl) maleimide 2 (0,100 g, 0.5 mmol) were dissolved in dry acetonitrile (20 ml). Et 3 N (0.404 g, 4 mmol) was added dropwise into the mixture with stirring and after addition was completed, the reaction mixture was stirred at room temperature for 2 h. The progress of the reaction was monitored by TLC. When the starting materials disappeared, the solvent, CH 3 CN was evaporated under the reduced pressure and the crude reaction mixture was taken into water (50 ml) to remove Et 3 N.HCl. The crude precipitated product was filtered and washed thoroughly with water, then n-hexane and dried under vacuum. After purification on a supplementary materials sup-2 Chromatotron (Centrifugal Thin-Layer Chromatograph) using n-hexane-ethyl acetate (2:1) as eluant and recrystallization from acetic acid yielded cycloadduct 3.  , 4.35; N, 9.07; found C, 66.45; H, 4.50; N, 8.74.

Refinement
H atoms on C were placed in idealized positions with C-H distances 0.95 -1.00 Å and there after treated as riding. A torsional parameter was refined for the methyl group. U iso for H were assigned as 1.2 times U eq of the attached atoms (1.5 for methyl). Fig. 1. The molecular structure of compound (I), showing the atom-labeling scheme. Displacement ellipsoids are drawn at the 50% probability level, with H atoms having arbitrary radius.