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organic compounds
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6-Methyl-N-(2-methylphenyl)-3-phenyl-1,6-dihydro-1,2,4,5-tetrazine-1-carboxamide
aCollege of Pharmaceutical Science, Zhejiang University of Technology, Hangzhou 310032, People's Republic of China
*Correspondence e-mail: huyang@mail.hz.zj.cn
In the title compound, C17H16N5O, the central tetrazine ring adopts an unsymmetrical boat conformation with the two C atoms as flagpoles. This compound can be considered as having homoaromaticity. The is stabilized by intermolecular C—H⋯O interactions between a benzene H atom and the carbonyl O atom.
Related literature
For related literature, see: Hu et al. (2004, 2005
); Jennison et al. (1986
); Sauer (1996
); Stam et al. (1982
); Xu et al. (2006
).
Experimental
Crystal data
|
Refinement
|
|
Data collection: SMART (Bruker, 2005); cell SAINT (Bruker, 2005
); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008
); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008
); molecular graphics: SHELXTL (Sheldrick, 2008
); software used to prepare material for publication: SHELXTL.
Supporting information
10.1107/S1600536808020199/lx2060sup1.cif
contains datablocks global, I. DOI:Structure factors: contains datablock I. DOI: 10.1107/S1600536808020199/lx2060Isup2.hkl
6-methyl-3-phenyl-1,6-dihydro-1,2,4,5-tetrazine (3.0 mmol), chloroform (10 ml) and pyridine (0.25 ml, 3.1 mmol) were mixed. 1-isocyanato-2-methylbenzene (3.0 mmol) in chloroform (10 ml) was added dropwise with stirring at room temperature. After the starting 1,6-dihydro-1,2,4,5-tetrazine was completely consumed (the reaction courses was monitored by TLC, dichloromethane system), evaporation of the chloroform, crude N-(o-methylphenyl) 3-phenyl-6-methyl-1,6-dihydro-1,2,4,5-tetrazine-1-carboxamide was obtained and purified by preparative δ p.p.m.: 8.64 (s, 1H), 8.14–8.16 (m, 2H, ArH), 7.92 (d, 1H, J = 8.0 Hz), 7.52–7.55 (m, 3H, ArH), 7.22 (m, 2H, ArH), 7.08 (t, 1H, J = 7.2 Hz), 6.91 (q, 1H, J=6.4 Hz), 2.34 (s, 3H), 1.09 (d, 3H, J = 6.8 Hz).
over silica gel PF254 (2 mm) (dichloromethane:petroleum ether = 1:1). The solution of the compound in anhydrous ethanol was concentrated gradually at room temperature to afford single crystals, which was suitable for X-ray diffraction. m.p. 378–380 K. Spectroscopic analysis: 1H NMR (CDCl3)The positions of H atoms bound to C17 and N5 were obtained from difference Fourier map and refined isotropically. Other H atoms were placed in calculated positions with C—H = 0.93 (aromatic) and 0.96 Å (methyl), and refined in riding model, with Uiso(H) = 1.5Ueq(C)for methyl and 1.2Ueq for aromatic H atoms.
Data collection: SMART (Bruker, 2005); cell
SAINT (Bruker, 2005); data reduction: SAINT (Bruker, 2005); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).C17H16N5O | F(000) = 644 |
Mr = 306.35 | Dx = 1.276 Mg m−3 |
Monoclinic, P21/c | Melting point = 378–380 K |
Hall symbol: -P 2ybc | Mo Kα radiation, λ = 0.71073 Å |
a = 13.941 (6) Å | Cell parameters from 742 reflections |
b = 5.675 (2) Å | θ = 3.2–24.8° |
c = 20.614 (8) Å | µ = 0.08 mm−1 |
β = 102.055 (6)° | T = 291 K |
V = 1594.9 (11) Å3 | Prism, red |
Z = 4 | 0.12 × 0.10 × 0.06 mm |
Bruker SMART APEX CCD area-detector diffractometer | 3116 independent reflections |
Radiation source: fine-focus sealed tube | 1882 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.084 |
Detector resolution: 10.0 pixels mm-1 | θmax = 26.0°, θmin = 1.5° |
ϕ and ω scans | h = −17→8 |
Absorption correction: multi-scan (SADABS; Sheldrick, 1996) | k = −6→7 |
Tmin = 0.980, Tmax = 0.995 | l = −25→25 |
6815 measured reflections |
Refinement on F2 | Secondary atom site location: difference Fourier map |
Least-squares matrix: full | Hydrogen site location: inferred from neighbouring sites |
R[F2 > 2σ(F2)] = 0.072 | H atoms treated by a mixture of independent and constrained refinement |
wR(F2) = 0.193 | w = 1/[σ2(Fo2) + (0.1133P)2] where P = (Fo2 + 2Fc2)/3 |
S = 0.94 | (Δ/σ)max < 0.001 |
3116 reflections | Δρmax = 0.54 e Å−3 |
226 parameters | Δρmin = −0.31 e Å−3 |
0 restraints | Extinction correction: SHELXL97 (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
Primary atom site location: structure-invariant direct methods | Extinction coefficient: 0.031 (5) |
C17H16N5O | V = 1594.9 (11) Å3 |
Mr = 306.35 | Z = 4 |
Monoclinic, P21/c | Mo Kα radiation |
a = 13.941 (6) Å | µ = 0.08 mm−1 |
b = 5.675 (2) Å | T = 291 K |
c = 20.614 (8) Å | 0.12 × 0.10 × 0.06 mm |
β = 102.055 (6)° |
Bruker SMART APEX CCD area-detector diffractometer | 3116 independent reflections |
Absorption correction: multi-scan (SADABS; Sheldrick, 1996) | 1882 reflections with I > 2σ(I) |
Tmin = 0.980, Tmax = 0.995 | Rint = 0.084 |
6815 measured reflections |
R[F2 > 2σ(F2)] = 0.072 | 0 restraints |
wR(F2) = 0.193 | H atoms treated by a mixture of independent and constrained refinement |
S = 0.94 | Δρmax = 0.54 e Å−3 |
3116 reflections | Δρmin = −0.31 e Å−3 |
226 parameters |
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes. |
Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > 2sigma(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger. |
x | y | z | Uiso*/Ueq | ||
O | 0.79549 (13) | 0.2358 (3) | 0.73526 (8) | 0.0685 (5) | |
N1 | 0.82379 (14) | 0.4541 (3) | 0.64939 (9) | 0.0552 (5) | |
N2 | 0.79315 (13) | 0.5181 (3) | 0.58485 (9) | 0.0522 (5) | |
N3 | 0.88534 (17) | 0.8632 (4) | 0.61618 (12) | 0.0685 (6) | |
N4 | 0.91853 (17) | 0.7948 (4) | 0.67409 (12) | 0.0724 (6) | |
N5 | 0.68918 (15) | 0.2115 (4) | 0.63448 (10) | 0.0598 (6) | |
H5N | 0.6759 (17) | 0.282 (4) | 0.5967 (12) | 0.054 (6)* | |
C1 | 0.91906 (18) | 0.5354 (4) | 0.68427 (11) | 0.0587 (6) | |
C2 | 0.83633 (17) | 0.7032 (4) | 0.56768 (11) | 0.0526 (6) | |
C3 | 0.82173 (17) | 0.7755 (4) | 0.49788 (12) | 0.0542 (6) | |
C4 | 0.77371 (19) | 0.6256 (5) | 0.44798 (12) | 0.0644 (7) | |
H4 | 0.7490 | 0.4824 | 0.4592 | 0.077* | |
C5 | 0.7624 (2) | 0.6873 (6) | 0.38197 (14) | 0.0813 (9) | |
H5 | 0.7307 | 0.5853 | 0.3491 | 0.098* | |
C6 | 0.7975 (2) | 0.8971 (6) | 0.36496 (16) | 0.0825 (9) | |
H6 | 0.7889 | 0.9392 | 0.3205 | 0.099* | |
C7 | 0.8452 (3) | 1.0452 (6) | 0.41287 (18) | 0.0876 (10) | |
H7 | 0.8701 | 1.1870 | 0.4009 | 0.105* | |
C8 | 0.8571 (2) | 0.9862 (5) | 0.47985 (15) | 0.0788 (8) | |
H8 | 0.8889 | 1.0897 | 0.5123 | 0.095* | |
C9 | 0.76906 (18) | 0.2904 (4) | 0.67787 (11) | 0.0535 (6) | |
C10 | 0.61865 (18) | 0.0506 (4) | 0.64801 (11) | 0.0559 (6) | |
C11 | 0.6437 (2) | −0.1223 (5) | 0.69669 (13) | 0.0724 (8) | |
H11 | 0.7077 | −0.1329 | 0.7210 | 0.087* | |
C12 | 0.5740 (3) | −0.2762 (6) | 0.70856 (15) | 0.0883 (10) | |
H12 | 0.5905 | −0.3910 | 0.7412 | 0.106* | |
C13 | 0.4807 (3) | −0.2619 (6) | 0.67292 (18) | 0.0928 (11) | |
H13 | 0.4330 | −0.3646 | 0.6817 | 0.111* | |
C14 | 0.4564 (2) | −0.0944 (6) | 0.62345 (16) | 0.0817 (9) | |
H14 | 0.3926 | −0.0891 | 0.5987 | 0.098* | |
C15 | 0.52429 (19) | 0.0652 (4) | 0.60974 (12) | 0.0601 (7) | |
C16 | 1.00241 (18) | 0.4238 (5) | 0.65920 (13) | 0.0658 (7) | |
H16A | 1.0013 | 0.2564 | 0.6656 | 0.099* | |
H16B | 1.0636 | 0.4865 | 0.6832 | 0.099* | |
H16C | 0.9955 | 0.4575 | 0.6128 | 0.099* | |
C17 | 0.4969 (3) | 0.2482 (6) | 0.55605 (17) | 0.0790 (8) | |
H17A | 0.431 (3) | 0.232 (5) | 0.5290 (16) | 0.102 (10)* | |
H17B | 0.543 (2) | 0.223 (5) | 0.5212 (15) | 0.092 (9)* | |
H17C | 0.511 (3) | 0.408 (7) | 0.5726 (16) | 0.107 (11)* |
U11 | U22 | U33 | U12 | U13 | U23 | |
O | 0.0755 (12) | 0.0808 (13) | 0.0475 (10) | −0.0050 (9) | 0.0090 (8) | 0.0014 (7) |
N1 | 0.0491 (11) | 0.0653 (12) | 0.0486 (10) | −0.0056 (10) | 0.0039 (8) | 0.0001 (8) |
N2 | 0.0469 (11) | 0.0556 (11) | 0.0529 (11) | −0.0018 (9) | 0.0077 (8) | 0.0026 (8) |
N3 | 0.0682 (14) | 0.0511 (12) | 0.0823 (15) | −0.0009 (10) | 0.0067 (12) | −0.0101 (10) |
N4 | 0.0740 (15) | 0.0636 (14) | 0.0742 (15) | −0.0012 (11) | 0.0030 (12) | −0.0181 (11) |
N5 | 0.0537 (12) | 0.0737 (14) | 0.0501 (12) | −0.0109 (10) | 0.0064 (10) | 0.0102 (9) |
C1 | 0.0521 (15) | 0.0578 (14) | 0.0616 (14) | −0.0068 (12) | 0.0015 (11) | −0.0095 (10) |
C2 | 0.0488 (13) | 0.0424 (12) | 0.0658 (14) | 0.0002 (11) | 0.0098 (11) | −0.0017 (9) |
C3 | 0.0427 (13) | 0.0485 (13) | 0.0722 (15) | 0.0022 (10) | 0.0137 (11) | 0.0085 (10) |
C4 | 0.0610 (16) | 0.0681 (16) | 0.0637 (15) | −0.0068 (13) | 0.0123 (12) | 0.0116 (11) |
C5 | 0.0763 (19) | 0.101 (2) | 0.0649 (16) | −0.0060 (17) | 0.0117 (14) | 0.0133 (14) |
C6 | 0.0736 (19) | 0.095 (2) | 0.0832 (19) | 0.0109 (18) | 0.0271 (16) | 0.0321 (17) |
C7 | 0.094 (2) | 0.0653 (19) | 0.115 (3) | −0.0012 (17) | 0.047 (2) | 0.0308 (17) |
C8 | 0.084 (2) | 0.0583 (17) | 0.098 (2) | −0.0070 (15) | 0.0271 (16) | 0.0097 (14) |
C9 | 0.0520 (14) | 0.0604 (14) | 0.0484 (13) | 0.0014 (11) | 0.0111 (11) | −0.0033 (10) |
C10 | 0.0597 (15) | 0.0570 (14) | 0.0548 (13) | −0.0092 (12) | 0.0210 (11) | −0.0027 (10) |
C11 | 0.0846 (19) | 0.0703 (17) | 0.0646 (15) | −0.0100 (15) | 0.0209 (14) | 0.0082 (12) |
C12 | 0.119 (3) | 0.080 (2) | 0.0732 (18) | −0.028 (2) | 0.035 (2) | 0.0027 (14) |
C13 | 0.106 (3) | 0.089 (2) | 0.097 (2) | −0.042 (2) | 0.053 (2) | −0.0174 (18) |
C14 | 0.0644 (18) | 0.090 (2) | 0.096 (2) | −0.0193 (16) | 0.0277 (16) | −0.0261 (17) |
C15 | 0.0571 (16) | 0.0621 (15) | 0.0645 (14) | −0.0049 (12) | 0.0205 (12) | −0.0115 (11) |
C16 | 0.0513 (15) | 0.0635 (16) | 0.0779 (16) | −0.0031 (12) | 0.0029 (12) | 0.0007 (11) |
C17 | 0.064 (2) | 0.078 (2) | 0.087 (2) | 0.0031 (17) | −0.0032 (17) | −0.0037 (16) |
O—C9 | 1.204 (3) | C7—C8 | 1.397 (4) |
N1—N2 | 1.359 (3) | C7—H7 | 0.9300 |
N1—C9 | 1.406 (3) | C8—H8 | 0.9300 |
N1—C1 | 1.447 (3) | C10—C15 | 1.388 (4) |
N2—C2 | 1.296 (3) | C10—C11 | 1.395 (4) |
N3—N4 | 1.249 (3) | C11—C12 | 1.366 (4) |
N3—C2 | 1.416 (3) | C11—H11 | 0.9300 |
N4—C1 | 1.487 (3) | C12—C13 | 1.356 (5) |
N5—C9 | 1.351 (3) | C12—H12 | 0.9300 |
N5—C10 | 1.412 (3) | C13—C14 | 1.383 (5) |
N5—H5N | 0.86 (2) | C13—H13 | 0.9300 |
C1—C16 | 1.506 (3) | C14—C15 | 1.381 (4) |
C2—C3 | 1.469 (3) | C14—H14 | 0.9300 |
C3—C8 | 1.374 (4) | C15—C17 | 1.508 (4) |
C3—C4 | 1.394 (4) | C16—H16A | 0.9600 |
C4—C5 | 1.382 (4) | C16—H16B | 0.9600 |
C4—H4 | 0.9300 | C16—H16C | 0.9600 |
C5—C6 | 1.361 (4) | C17—H17A | 0.98 (4) |
C5—H5 | 0.9300 | C17—H17B | 1.07 (3) |
C6—C7 | 1.360 (5) | C17—H17C | 0.97 (4) |
C6—H6 | 0.9300 | ||
N2—N1—C9 | 119.9 (2) | O—C9—N5 | 127.3 (2) |
N2—N1—C1 | 118.0 (2) | O—C9—N1 | 119.9 (2) |
C9—N1—C1 | 121.7 (2) | N5—C9—N1 | 112.8 (2) |
C2—N2—N1 | 114.5 (2) | C15—C10—C11 | 121.1 (2) |
N4—N3—C2 | 120.2 (2) | C15—C10—N5 | 117.7 (2) |
N3—N4—C1 | 115.6 (2) | C11—C10—N5 | 121.1 (2) |
C9—N5—C10 | 126.5 (2) | C12—C11—C10 | 119.9 (3) |
C9—N5—H5N | 115.8 (16) | C12—C11—H11 | 120.1 |
C10—N5—H5N | 117.0 (16) | C10—C11—H11 | 120.1 |
N1—C1—N4 | 105.6 (2) | C13—C12—C11 | 120.2 (3) |
N1—C1—C16 | 112.9 (2) | C13—C12—H12 | 119.9 |
N4—C1—C16 | 110.4 (2) | C11—C12—H12 | 119.9 |
N2—C2—N3 | 120.7 (2) | C12—C13—C14 | 120.0 (3) |
N2—C2—C3 | 121.1 (2) | C12—C13—H13 | 120.0 |
N3—C2—C3 | 117.4 (2) | C14—C13—H13 | 120.0 |
C8—C3—C4 | 118.4 (2) | C15—C14—C13 | 122.0 (3) |
C8—C3—C2 | 121.6 (2) | C15—C14—H14 | 119.0 |
C4—C3—C2 | 120.0 (2) | C13—C14—H14 | 119.0 |
C5—C4—C3 | 120.7 (2) | C14—C15—C10 | 116.9 (2) |
C5—C4—H4 | 119.7 | C14—C15—C17 | 121.5 (3) |
C3—C4—H4 | 119.7 | C10—C15—C17 | 121.5 (2) |
C6—C5—C4 | 120.2 (3) | C1—C16—H16A | 109.5 |
C6—C5—H5 | 119.9 | C1—C16—H16B | 109.5 |
C4—C5—H5 | 119.9 | H16A—C16—H16B | 109.5 |
C7—C6—C5 | 120.1 (3) | C1—C16—H16C | 109.5 |
C7—C6—H6 | 120.0 | H16A—C16—H16C | 109.5 |
C5—C6—H6 | 120.0 | H16B—C16—H16C | 109.5 |
C6—C7—C8 | 120.6 (3) | C15—C17—H17A | 114.5 (19) |
C6—C7—H7 | 119.7 | C15—C17—H17B | 107.6 (16) |
C8—C7—H7 | 119.7 | H17A—C17—H17B | 104 (2) |
C3—C8—C7 | 120.1 (3) | C15—C17—H17C | 112.6 (19) |
C3—C8—H8 | 120.0 | H17A—C17—H17C | 113 (3) |
C7—C8—H8 | 120.0 | H17B—C17—H17C | 105 (3) |
C9—N1—N2—C2 | 166.3 (2) | C4—C3—C8—C7 | −0.5 (4) |
C1—N1—N2—C2 | −21.5 (3) | C2—C3—C8—C7 | 177.5 (3) |
C2—N3—N4—C1 | 10.6 (3) | C6—C7—C8—C3 | 1.0 (5) |
N2—N1—C1—N4 | 52.3 (3) | C10—N5—C9—O | 1.3 (4) |
C9—N1—C1—N4 | −135.5 (2) | C10—N5—C9—N1 | −178.6 (2) |
N2—N1—C1—C16 | −68.4 (3) | N2—N1—C9—O | −179.1 (2) |
C9—N1—C1—C16 | 103.7 (2) | C1—N1—C9—O | 8.9 (3) |
N3—N4—C1—N1 | −45.4 (3) | N2—N1—C9—N5 | 0.8 (3) |
N3—N4—C1—C16 | 77.0 (3) | C1—N1—C9—N5 | −171.2 (2) |
N1—N2—C2—N3 | −19.4 (3) | C9—N5—C10—C15 | 152.7 (2) |
N1—N2—C2—C3 | 171.32 (19) | C9—N5—C10—C11 | −29.4 (4) |
N4—N3—C2—N2 | 25.8 (3) | C15—C10—C11—C12 | −2.0 (4) |
N4—N3—C2—C3 | −164.6 (2) | N5—C10—C11—C12 | −179.8 (2) |
N2—C2—C3—C8 | 171.8 (2) | C10—C11—C12—C13 | 0.3 (4) |
N3—C2—C3—C8 | 2.2 (3) | C11—C12—C13—C14 | 1.4 (5) |
N2—C2—C3—C4 | −10.2 (4) | C12—C13—C14—C15 | −1.6 (5) |
N3—C2—C3—C4 | −179.8 (2) | C13—C14—C15—C10 | 0.0 (4) |
C8—C3—C4—C5 | 0.3 (4) | C13—C14—C15—C17 | −179.5 (3) |
C2—C3—C4—C5 | −177.7 (2) | C11—C10—C15—C14 | 1.8 (3) |
C3—C4—C5—C6 | −0.5 (4) | N5—C10—C15—C14 | 179.7 (2) |
C4—C5—C6—C7 | 1.0 (5) | C11—C10—C15—C17 | −178.7 (3) |
C5—C6—C7—C8 | −1.2 (5) | N5—C10—C15—C17 | −0.8 (3) |
D—H···A | D—H | H···A | D···A | D—H···A |
C6—H6···Oi | 0.93 | 2.56 | 3.385 (3) | 148 |
Symmetry code: (i) x, −y+3/2, z−1/2. |
Experimental details
Crystal data | |
Chemical formula | C17H16N5O |
Mr | 306.35 |
Crystal system, space group | Monoclinic, P21/c |
Temperature (K) | 291 |
a, b, c (Å) | 13.941 (6), 5.675 (2), 20.614 (8) |
β (°) | 102.055 (6) |
V (Å3) | 1594.9 (11) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 0.08 |
Crystal size (mm) | 0.12 × 0.10 × 0.06 |
Data collection | |
Diffractometer | Bruker SMART APEX CCD area-detector diffractometer |
Absorption correction | Multi-scan (SADABS; Sheldrick, 1996) |
Tmin, Tmax | 0.980, 0.995 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 6815, 3116, 1882 |
Rint | 0.084 |
(sin θ/λ)max (Å−1) | 0.617 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.072, 0.193, 0.94 |
No. of reflections | 3116 |
No. of parameters | 226 |
H-atom treatment | H atoms treated by a mixture of independent and constrained refinement |
Δρmax, Δρmin (e Å−3) | 0.54, −0.31 |
Computer programs: SMART (Bruker, 2005), SAINT (Bruker, 2005), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), SHELXTL (Sheldrick, 2008).
D—H···A | D—H | H···A | D···A | D—H···A |
C6—H6···Oi | 0.93 | 2.56 | 3.385 (3) | 147.7 |
Symmetry code: (i) x, −y+3/2, z−1/2. |
Acknowledgements
The authors are very grateful to the National Natural and Scientific Foundation (grant No. 20272053) for financial support.
References
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1,2,4,5-Tetrazine derivatives have high potential for biological activity, possessing a wide spectrum of antiviral and antitumor properties. They have been widely used in pesticides and herbicides (Sauer, 1996). Dihydro-1,2,4,5-tetrazine has four isomers, namely 1,2-, 1,4-, 1,6-, and 3,6-dihydro-1,2,4,5-tetrazines. The 1,6-dihydro structures (Stam et al., 1982; Jennison et al., 1986) were found, by X-ray diffraction, to be homoaromatic. In continuation of our work on the structure–activity relationship of 1,6-dihydro-1,2,4,5-tetrazine derivatives (Hu et al., 2004, 2005), we report the crystal structure of the title compound (I) (Fig. 1).
In the tetrazine ring, atoms N1, N2, N3 and N4 are coplanar, while atoms C1 and C2 deviate from the plane by 0.597 (3) and 0.225 (3)°, respectively. The N1/C1/N4 and N2/C3/N3 planes make dihedral angles of 42.3 (2)° and 19.7 (2)°, respectively, with the N1–N4 plane, i.e. the tetrazine ring adopts an unsymmetrical boat conformation. The C3–C8 benzene ring make dihedral angles of 13.2 (1)°, with the N1–N4 plane. N1 is almost sp2 hybridized due to the angles around it add up to 359.6 (2)°. In keeping with similar situations in 3-phenyl-6-ethyl-1,6-dihydro-1,2,4,5-tetrazine (Stam et al., 1982), 3-(p-chlorophenyl)-6-methyl-1,6-dihydro-1,2,4,5-tetrazine (Xu et al., 2006) and 1-acetyl-3,6-dimethyl-1,2,4,5-tetrazine (Jennison et al., 1986), it can be considered that the molecule is homoaromatic.
The Fig. 2 shows that intramolecular C—H···O hydrogen bonds form a pseudo-five-membered ring. The crystal packing (Fig. 2) is stabilized by intermolecular C—H···O interactions between a benzene H atom and the O atom of carbonyl group, with a C6—H6···Oi separation of 3.385 (3) Å (Table 1; symmetry code as in Fig. 2).