1-tert-Butyl 2-ethyl 5-bromo-3-(thiophen-2-ylcarbonyl)-1H-indole-1,2-dicarboxylate

In the title compound, C21H20BrNO5S, the thiophene group is located above the mean plane of the indole ring and displays rotational disorder (i.e. rotation through 180°). The site occupancy of the major component is 0.902 (2), while that of the minor component is 0.098 (2). In the crystal, pairs of weak C—H⋯O interactions link the molecules into centrosymmetric dimers.

In the title compound, C 21 H 20 BrNO 5 S, the thiophene group is located above the mean plane of the indole ring and displays rotational disorder (i.e. rotation through 180 ). The site occupancy of the major component is 0.902 (2), while that of the minor component is 0.098 (2). In the crystal, pairs of weak C-HÁ Á ÁO interactions link the molecules into centrosymmetric dimers.

Related literature
For background to the use of indoles as scaffolds in the synthesis of HIV-agents, see:  and for a recent review on stages of non-nucleoside reverse transcriptase inhibitors, see: Reynolds et al. (2012). For the crystal structures of closely related compounds, see: Beddoes et al. (1986), Hassam & Smith (2012 Table 1 Hydrogen-bond geometry (Å , ).
MH thanks Professor Willem A. L. van Otterlo and Dr S. C. Pelly for their valuable input and research oversight. Stellenbosch University's Science Faculty is also acknowledged for providing laboratory space and financial research support (Subcommittee B). The South African National Research Foundation (NRF), Pretoria, is also acknowledged for providing research funds.
The title compound, C 21 H 20 BrNO 5 S, crystallizes with one molecule in the asymmetric unit (Fig. 1). The thiophene moiety is disordered over two positions with major (A) and minor (B) components in a 0.9021 (19):0.0979 (19)(2) ratio.

Refinement
All non-hydrogen atoms were refined anisotropically. H atoms were placed geometrically [C-H = 0.95 -0.99 Å; with U iso (H) = 1.2 -1.5U eq (C)] and constrained to ride on their parent atoms. The site-occupancy factors of the disordered thiophene moieties were initially set to 0.5 and then refined, leading to an occupancy of 0.9021 (19) and 0.0979 (19)(2) for the major and minor components, respectively. Bond lengths for the thiophene and phenyl moieties were restrained using the SHELXL SADI command (s.u. = 0.002 Å). Atom displacement parameters for overlaping atoms of the disordered models were constrained using EADP.

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.