(E)-3-[(Dimethylamino)methylidene]-4-phenyl-1-(prop-2-ynyl)-1H-1,5-benzodiazepin-2(3H)-one

The title compound, C21H19N3O, exhibits an E configuration with respect to the C=C bond between the benzodiazepine and trimethylamine groups. The seven-membered diazepine ring displays a boat conformation. In the crystal, molecules are linked by a C—H⋯O hydrogen bond, forming a chain along [110].

The title compound, C 21 H 19 N 3 O, exhibits an E configuration with respect to the C C bond between the benzodiazepine and trimethylamine groups. The seven-membered diazepine ring displays a boat conformation. In the crystal, molecules are linked by a C-HÁ Á ÁO hydrogen bond, forming a chain along [110]. 228 parameters H-atom parameters constrained Á max = 0.16 e Å À3 Á min = À0.14 e Å À3 Table 1 Hydrogen-bond geometry (Å , ).

Comment
The benzodiazepine nucleus is extremely important, as it is the base of several drugs and other biologically active compounds with different properties. A large number of structurally modified benzodiazepines have been prepared and evaluated concerning their biological activity (Di Braccio et al., 2001;Pevarello et al., 1993) and may be considered support for the synthesis of more active heterocyclic systems. In this class of compounds, our research team is interested in the synthesis of novel benzodiazepines derived (Loughzail et al., 2011;Boudina et al., 2006). Here we wish to report the synthesis via phase transfer catalysis and the crystallographic studies of the title compound. The title compound was prepared by action of propargyl bromide with 3-dimethylaminomethylene-4-phenyl-1,3-dihydro-2H-1,5benzodiazepin-2-one using a catalytic amount of benzyltriethylammonium chloride (TBA-Cl) and sodium hydroxide aqueous solution in benzene. The obtained compound was typically characterized by 1 H, 13 C NMR, IR and mass spectroscopy, and the stereochemistry (E) of the benzodiazepine was determined by X-ray diffraction. The main geometric feature of the title compound is in good agreement with that observed in a similar compound (Loughzail et al., 2011).

Experimental
A mixture of 0.6 g (2.06 mmol) of 3-[(dimethylamino)methylene]-4-phenyl-1,3-dihydro-2H-1,5-benzodiazepin-2-one, 0.26 g (1.14 mmol) of benzyltriethylammonium chloride and 3 ml of a 50% sodium hydroxide aqueous solution in benzene (25 ml) was stirred at ambient temperature. After 15 min, propagyl bromide was added slowly. After 8 h of stirring at 298 K, the reaction mixture was diluted with water (30 ml). The organic layer was extracted with benzene (3× 10 ml), dried over anhydrous sodium sulfate and evaporated under vacuum. The title compound was isolated by column chromatography on silica gel using hexane/ethyl acetate as eluent. The solid product was recrystallized in dichloromethane to give yellow crystals of the title compound.

Refinement
All H-atoms were located in a difference map and refined using a riding model with C-H = 0.93-0.97 Å, and with U iso = 1.2U eq (C).

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.