4-[2-(2-Benzylidenehydrazinylidene)-3,6-dihydro-2H-1,3,4-thiadiazin-5-yl]-3-(4-methoxyphenyl)sydnone

In the title compound, C19H16N6O3S, the 3,6-dihydro-1,3,4-thiadiazine ring adopts a twist-boat conformation. The dihedral angle between the methoxy-substituted benzene ring and the oxadiazole ring is 71.91 (7)°. In the crystal structure, centrosymmetrically related molecules are linked into dimers via pairs of intermolecular N—H⋯N hydrogen bonds, generating R 2 2(8) ring motifs. There is an intramolecular C—H⋯O hydrogen bond which generates an S(6) ring motif.

In the title compound, C 19 H 16 N 6 O 3 S, the 3,6-dihydro-1,3,4thiadiazine ring adopts a twist-boat conformation. The dihedral angle between the methoxy-substituted benzene ring and the oxadiazole ring is 71.91 (7) . In the crystal structure, centrosymmetrically related molecules are linked into dimers via pairs of intermolecular N-HÁ Á ÁN hydrogen bonds, generating R 2 2 (8) ring motifs. There is an intramolecular C-HÁ Á ÁO hydrogen bond which generates an S(6) ring motif.

Comment
Sydnones constitute a well defined class of mesoionic compounds consisting of 1,2,3-oxadiazole ring system. The introduction of the concept of mesoionic structure for certain heterocyclic compounds in the year 1949 has proved to be a fruitful development in heterocyclic chemistry (Baker et al., 1949). The study of sydnones still remains a field of interest because of their electronic structures and also because of the various types of biological activities displayed by some of them. Interest in sydnone derivatives has also been encouraged by the discovery that they exhibit various pharmacological activities (Hedge et al., 2008;Rai et al., 2008). Encouraged by these reports and in continuation of our research for biologically active nitrogencontaining heterocycles, a thiadiazine moiety at the 4-position of the phenylsydnone was introduced. A series of thiadiazines were synthesized by the condensation of 4-bromoacetyl-3-arylsydnones with N'-[phenylmethylidene]carbonohydrazide. 4-Bromoacetyl-3-arylsydnones were in turn obtained by the photochemical bromination of 4-acetyl-3-arylsydnones (Kalluraya et al., 2003).

Experimental
To a mixture of 4-bromoacetyl-3-(p-anisyl)sydnone (0.01 mol) and N'-(phenylmethylidene) carbonohydrazide (0.01 mol) in ethanol, a catalytic amount of anhydrous sodium acetate was added. The solution was stirred at room temperature for 2-3 hours. The solid product that separated out was filtered and dried. It was then recrystallized from ethanol. Crystals suitable for X-ray analysis were obtained by slow evaporation of a DMF/ethanol solution (1:2 v/v).

Refinement
Atom H1N3 was located from a difference Fourier map and refined freely [N-H = 0.87 (2) Å]. The remaining H atoms were positioned geometrically [C-H = 0.93-0.97 Å] and were refined using a riding model, with U iso (H) = 1.2 U eq (C) or 1.5 U eq (C) for methyl H atoms. Fig. 1. The asymmetric unit of the title compound, showing 30% probability displacement ellipsoids. The intramolecular hydrogen bond is shown as a dashed line.  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 > 2σ(F 2 ) is used only for calculating Rfactors(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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq S1 0.51196 (