6-Methyl-2,3,4,9-tetrahydro-1H-carbazole-1-thione

In the title molecule, C13H13NS, the dihedral angle between the benzene ring and the fused pyrrole ring is 0.71 (8)° and the cyclohexene ring is in an envelope form. The (CH2)3 atoms of the cyclohexene ring are disordered over two positions; the site-occupancy factor for the major component refined to 0.862 (4). In the crystal, intermolecular N—H⋯S hydrogen bonds lead to the formation of centrosymmetric aggregates via an R 2 2(10) ring.

In the title molecule, C 13 H 13 NS, the dihedral angle between the benzene ring and the fused pyrrole ring is 0.71 (8) and the cyclohexene ring is in an envelope form. The (CH 2 ) 3 atoms of the cyclohexene ring are disordered over two positions; the site-occupancy factor for the major component refined to 0.862 (4). In the crystal, intermolecular N-HÁ Á ÁS hydrogen bonds lead to the formation of centrosymmetric aggregates via an R 2 2 (10) ring.
RJB acknowledges the NSF MRI program (grant No. CHE-0619278) for funds to purchase an X-ray diffractometer.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: TK2746).

Comment
The development of methods for the synthesis of fused carbazole nuclei is becoming increasingly important as a result of the number of natural and synthetic carbazoles that display biological activity (Pelly et al., 2005). Heterocycle-annulated tetra-, penta-and hexa-cyclic carbazole derivatives have been developed using successive applications of three atom economic processes, viz., Claisen rearrangement, olefin metathesis and Diels-Alder reactions (Chattopadhyay et al., 2006). The preparation of 1-oxo compounds via their corresponding hydrazones has been reported (Rajendra Prasad & Vijayalakshmi, 1994  In the title molecule, Fig. 1, the dihedral angle between the benzene ring and the fused pyrrole ring is 0.71 (8) °. The cyclohexene ring is in envelope form. Three C atoms (C2A, C3A, C4A) of the cyclohexene ring, with their attached H atoms are disordered over two positions; the site-occupancy factors are ca 0.86 and 0.14. Intermolecular N-H···S hydrogen bonds form a R 2 2 (10) (Bernstein et al., 1995) ring in the crystal structure (Table 1 & Fig. 2).

Refinement
Atoms C2A, C3A, C4A of the cyclohexene ring, with attached hydrogen atoms are disordered over two positions; the site occupancy factors refined to 0.862 (4) and 0.138 (4). The N9-H atom was located in a difference Fourier map and refined freely. Other H atoms were positioned geometrically and allowed to ride on their parent atoms, with C-H = 0.93-0.97 Å and U iso (H) = xU eq (parent atom), where x = 1.5 for methyl and 1.2 for all other carbon-bound H atoms. A damping factor (damp 200 15 in the final refinement cycles) was applied to avoid large and erratic displacements of the hydrogen atoms of the less occupied C atoms.