Crystal structure of (±)-(3aR,5R,8bR)-5-hydroperoxy-2-phenyl-6-tosyl-4,5,6,8b-tetrahydropyrrolo[3,4-e]indole-1,3(2H,3aH)-dione

The title compound crystallized as racemic tandem OO—H⋯O=C hydrogen-bonded dimers stacked along [100] in the space group P . This is the first crystallographically characterized example of a hydroperoxide obtained from the autoxidation of a Diels–Alder adduct of a 2-vinyl five-membered heterocycle.


Figure 1
The molecular structure of (I) with displacement ellipsoids drawn at the 50% probability level.

Structural commentary
The N-phenyl, S-phenyl, and pyrrolo rings are individually planar within 0.009, 0.011, and 0.010 Å , respectively. The Nphenyl ring (C7-C11) is twisted 58.3 (2) out of plane from the imido moiety (C5, N2, C12, Figs. 2 and 4). The cyclohexene ring has a half-chair conformation with C14 out of plane in the direction anti-to the S-tolyl group (Figs. 2 and 4), which is bent 85.4 (2) out of plane with the pyrrolo ring, giving the molecule an overall L-or J-shape.

Supramolecular features
Interlocking pairs are aligned such that the axis of the S-tolyl group (C21) points toward the face of the cyclohexene ring (C3, C14, C15, Fig. 3). Hydrogen-bonded dimers form between H4O and O2 (  Two pairs of stacked tolyl groups, viewed along [112]. The central two molecules form an interlocked pair. Twisting of the N-Phenyl group, and out-of-plane position of C14, are also depicted.

Figure 3
The central interlocked pair from Fig. 2,viewed along [221]. The C20,C21-axis is aligned with the face of the cyclohexene ring of its interlocked partner.

Figure 5
The two tolyl-stacked pairs from Fig. 2

Database survey
The structures shown in Fig. 8 represent the cores of most compounds that could be obtained by Diels-Alder reactions of the type that gave title compound (I), using nitrogen heterocyclic dienes and dienophiles. Searching these substructures found six entries in the current database (Cambridge Structural Database, Version 5.35, November 2013;Allen 2002). Only two of these were synthesized by cycloadditions of this type [a combretastatin derivative (Ty et al., 2010); carbazomycin B (Beccali et al., 1996)]. Upon expanding the search to include any combination of heteroatoms at nitrogen and oxygen sites, seven additional entries were found, all within or closely related to the caesalmin family of furanoditerpenoid antivirals (i.e., Rodrigues et al., 2004;Jiang et al., 2002). Of 13 total entries, none was found containing sulfur atoms. Ten exhibit intermolecular hydrogen bonding, but only two of them are tandem-bonded dimers [pyrimidinone carbonyl to carboxylic acid (Obushak et al., 2011); succinimide dimerization between N-H and a carbonyl oxygen (Beccali et al., 1996)]. None of these structures resembles that of compound (I). Safety Note: Hydroperoxides, particularly those bearing an -proton (e.g., H15, Fig. 1), can be shock-or heat-sensitive and detonate violently (Francisco, 1993). Although sensitivity tests on our batch of title compound (I) were negative, appropriate precautions should be taken when reproducing or extending [192][193][194][195] research communications Table 1 Hydrogen-bond geometry (Å , ).

Figure 8
Substructures used for the database survey.
our work with (I) or similar compounds. Metal tools, glass or metal storage vessels, high oxygen-or nitrogen-to-carbon ratios, and large scales should all be avoided. The bulk of product should be kept in solution, with small aliquots being allowed to dry only as necessary.

Refinement
A direct-methods solution was calculated which provided most non-hydrogen atoms from the E-map. Full-matrix leastsquares/difference Fourier cycles were performed, which located the remaining non-hydrogen atoms. All non-hydrogen atoms were refined with anisotropic displacement parameters. All hydrogen atoms except for H4O were placed in ideal positions and refined as constrained atoms with U iso (H n ) = 1.2U eq (C n ), except for the methyl group, where U iso (H21 i ) = 1.5U eq (C21). The bond lengths (Å ) specified for C-H hydrogens were 0.93 (aryl), 0.96 (methyl), 0.97 (methylene), and 0.98 (methine). H4O was found from the difference Fourier map and refined with U iso (H4O) = 1.2U eq (O4) and an O-H bond length of 0.82 Å . The final full-matrix least-squares refinement converged to R1 = 0.0364 and wR2 = 0.1161 (F 2 , all data). Crystal data, data collection and structure refinement details are summarized in Table 2.

Computing details
Data collection: SMART (Bruker, 2001); cell refinement: SAINT (Bruker, 2003); data reduction: SAINT (Bruker, 2003); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: Mercury (Macrae et al., 2008); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008), enCIFer (Allen et al., 2004), and publCIF (Westrip, 2010). where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.27 e Å −3 Δρ min = −0.28 e Å −3 Special details Experimental. The space group P-1 was determined based on systematic absences and intensity statistics. 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.