1-(10H-phenothiazin-10-yl)ethanone

In the title compound, C14H11NOS, the phenothiazine unit has a butterfly conformation and the central six-membered ring has a boat form. The fold angle between the benzene rings is 46.39 (7)°, which is larger than found in similar compounds, probably as a result of steric repulsion between the phenothiazine fragment and the acetyl group.

In the title compound, C 14 H 11 NOS, the phenothiazine unit has a butterfly conformation and the central six-membered ring has a boat form. The fold angle between the benzene rings is 46.39 (7) , which is larger than found in similar compounds, probably as a result of steric repulsion between the phenothiazine fragment and the acetyl group.

1-(10H-phenothiazin-10-yl)ethanone Eri Tokunaga and Tsunehisa Okuno Comment
Phenothiazine derivatives have been interesting from the viewpoint of formation of charge-transfer complexes and biochemical reactivities. The title compound is an N-acetylated phenothiazine in which the orientation of the acetyl group is thought to determine the molecular structure and furthermore to affect the oxidation reactivity at 5-position.
The phenothiazine moiety has a butterfly structure, and the central six-membered ring has a boat form. The dihedral angle between the C1-C6 and C7-C12 planes is 133.61 (7)°, which is smaller than a usual angle (Chu & Van der Helm, 1974, 1975. The five atoms of N1, C1, C12, C13 and O1 lie on almost the same plane (the N1/C1/C12/Cl3/O1 plane: r.m.s. deviation = 0.0317 Å), showing efficient conjugation between the lone pair of N1 and the carbonyl group.
The proximity of C11 and C14 is indicated by the intramolecular contact distance of 3.130 (3) Å, although little effective contact is observed around O1. The relatively small dihedral angle between the benzene rings is thought to reduce the steric repulsion between the phenothiazine moiety and the acetyl group. There are three reports concerning 1-(10Hphenothiazin-10-yl)ethanone derivatives (Meester & Chu, 1986;Wang et al., 2009;Siddegowda et al., 2011). Similar steric effects can also be recognized in these cases.

Experimental
Single crystals with sufficient quality for X-ray crystallographical analysis were prepared by recrystallization from an ethanol solution.

Refinement
The C-bound H atoms were placed at ideal positions and were refined as riding on their parent C atoms. U iso (H) values of the H atoms were set at 1.2U eq (parent atom).

1-(10H-phenothiazin-10-yl)ethanone
Special details Refinement. Refinement was performed using all reflections. The weighted R-factor (wR) and goodness of fit (S) are based on F 2 . R-factor (gt) are based on F. The threshold expression of F 2 > 2.0 σ(F 2 ) is used only for calculating R-factor (gt).