Bruceolline J: 2-hydroxy-3,3-dimethyl-2,3-dihydrocyclopenta[b]indol-1(4H)-one

The 12-membered cyclopenta[b]indole ring system in the title compound, C13H13NO2, deviates only slightly from planarity (r.m.s. deviation = 0.051 Å). In the crystal, N—H⋯O and O—H⋯O hydrogen bonds link the molecules into sheets parallel to (100). The five-membered cyclopentanone ring is in slightly distorted envelope conformation with the C atom bearing the hydroxy substituent as the flap.

The 12-membered cyclopenta [b]indole ring system in the title compound, C 13 H 13 NO 2 , deviates only slightly from planarity (r.m.s. deviation = 0.051 Å ). In the crystal, N-HÁ Á ÁO and O-HÁ Á ÁO hydrogen bonds link the molecules into sheets parallel to (100). The five-membered cyclopentanone ring is in slightly distorted envelope conformation with the C atom bearing the hydroxy substituent as the flap.

Comment
Bruceolline J is a cyclopenta [b]indole alkaloid which has been recently isolated from the stems of Brucea mollis Wall (Chen et al., 2011). Our total synthesis of racemic bruceolline J was achieved by the oxidation of bruceolline D to bruceolline E with DDQ followed by the selective reduction of bruceolline E with sodium borohydride in 98% yield.
Enantioselective reductions with β-chlorodiisopinocampheylborane gave both the natural and unnatural enantiomers in excellent yields and enantioselectivites. Further isolation studies of the Brucea mollis shrubs have resulted in the discovery of a myriad of other bruceollines and cathan-6-one alkaloids (Ouyang et al., 1994a;Ouyang et al., 1994b;Ouyang et al., 1995). Although there has been limited attention from the synthetic community given to these compounds, a previous synthesis of bruceolline E has been reported (Jordan et al., 2011). The crystal structures of bruceolline D (Lopchuk et al., 2013) and bruceolline E (Jordon et al., 2012) have been disclosed. In view of the importance of cyclopenta[b]indole alkaloids, we report here the crystal structure of the title compound, C 13 H 13 NO 2 , (I).

Experimental
To an ice-cold solution of bruceolline E (50 mg, 0.234 mmol, 1.0 equiv.) in dry THF (10 mL) was added sodium borohydride (5 mg, 0.117 mmol, 0.5 equiv.) in one portion (Fig. 3). After stirring at 0°C for 5 minutes, the reaction was quenched with water (5 mL) and concentrated to half the original volume. The mixture was extracted with ethyl acetate (3 x 40 mL). The organic extracts were combined, dried over Na 2 SO 4 , and concentrated in vacuo to an off-white solid.
The residue was purified by flash chromatography (50% ethyl acetate in pentane) to afford the desired product (I) as a white solid (50 mg, 98% yield). Single crystals suitable for diffraction were grown from ethyl acetate (slow evaporation) at ambient temperature [m.p. 466-467 K (dec); no literature value available].

Refinement
All H atoms were found in a difference map. Nevertheless, they were placed in their calculated positions and then refined using the riding model with Atom-H lengths of 0.95Å, 1.000Å (CH), 0.98Å (CH 3 ), 0.88Å (NH) or 0.84Å (OH).
Isotropic displacement parameters for these atoms were set to 1.2 (CH, NH) or 1.5 (CH 3 , OH) times U eq of the parent atom. The methyl groups and the hydroxyl group were refined as rotating groups allowed to rotate but not to tip.

Computing details
Data collection: CrysAlis PRO (Agilent, 2012); cell refinement: CrysAlis PRO (Agilent, 2012); data reduction: CrysAlis PRO (Agilent, 2012); program(s) used to solve structure: SUPERFLIP (Palatinus & Chapuis, 2007); program(s) used to refine structure: SHELXL2012 (Sheldrick, 2008); molecular graphics: XP in SHELXTL (Sheldrick, 2008); software used to prepare material for publication: XP in SHELXTL (Sheldrick, 2008).   Synthesis of (I). Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.