Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270102005681/av1106sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S0108270102005681/av1106Isup2.hkl |
CCDC reference: 187935
A solution of 1-acetylisatin (0.05 M) in the presence of an excess of β-chloro-4-bromostyrene in benzene solution was irradiated with Pyrex-filtered light. After completion of the reaction, the solvent was removed in vacuo and the residue was separated using chromatography on a silica-gel column to afford (I). Single crystals suitable for the X-ray diffraction study were obtained by slow evaporation of an acetone-petroleum ether (3:1, v/v) solution.
The H atoms were geometrically fixed and treated as riding on the parent C atoms, with C—H = 0.93–0.97 Å and Uiso(H) = 1.2 Ueq(C). The highest peak and the deepest hole were found near atom Br1, at distances of 0.94 and 0.86 Å, respectively.
Data collection: SMART (Siemens, 1996); cell refinement: SAINT (Siemens, 1996); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 1997); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL, PARST (Nardelli, 1995) and PLATON (Spek, 1990).
C18H13BrClNO3 | Dx = 1.551 Mg m−3 |
Mr = 406.65 | Melting point: 382(1)K K |
Monoclinic, P21/c | Mo Kα radiation, λ = 0.71073 Å |
a = 18.5810 (5) Å | Cell parameters from 4889 reflections |
b = 12.5906 (4) Å | θ = 2.7–28.4° |
c = 7.4709 (2) Å | µ = 2.53 mm−1 |
β = 94.645 (1)° | T = 233 K |
V = 1742.05 (9) Å3 | Slab, colourless |
Z = 4 | 0.36 × 0.28 × 0.16 mm |
F(000) = 816 |
Siemens SMART CCD area-detector diffractometer | 4173 independent reflections |
Radiation source: fine-focus sealed tube | 2016 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.080 |
Detector resolution: 8.33 pixels mm-1 | θmax = 28.3°, θmin = 2.7° |
ω scans | h = −23→24 |
Absorption correction: empirical (using intensity measurements) (SADABS; Sheldrick, 1996) | k = −16→13 |
Tmin = 0.463, Tmax = 0.688 | l = −9→9 |
10113 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)] = 0.050 | H-atom parameters constrained |
wR(F2) = 0.120 | w = 1/[σ2(Fo2) + (0.0153P)2] where P = (Fo2 + 2Fc2)/3 |
S = 0.81 | (Δ/σ)max < 0.001 |
4173 reflections | Δρmax = 0.45 e Å−3 |
219 parameters | Δρmin = −0.76 e Å−3 |
0 restraints | Extinction correction: SHELXTL (Sheldrick, 1997), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
Primary atom site location: structure-invariant direct methods | Extinction coefficient: 0.0091 (10) |
C18H13BrClNO3 | V = 1742.05 (9) Å3 |
Mr = 406.65 | Z = 4 |
Monoclinic, P21/c | Mo Kα radiation |
a = 18.5810 (5) Å | µ = 2.53 mm−1 |
b = 12.5906 (4) Å | T = 233 K |
c = 7.4709 (2) Å | 0.36 × 0.28 × 0.16 mm |
β = 94.645 (1)° |
Siemens SMART CCD area-detector diffractometer | 4173 independent reflections |
Absorption correction: empirical (using intensity measurements) (SADABS; Sheldrick, 1996) | 2016 reflections with I > 2σ(I) |
Tmin = 0.463, Tmax = 0.688 | Rint = 0.080 |
10113 measured reflections |
R[F2 > 2σ(F2)] = 0.050 | 0 restraints |
wR(F2) = 0.120 | H-atom parameters constrained |
S = 0.81 | Δρmax = 0.45 e Å−3 |
4173 reflections | Δρmin = −0.76 e Å−3 |
219 parameters |
Experimental. The data collection covered over a hemisphere of reciprocal space by a combination of three sets of exposures; each set had a different ϕ angle (0, 88 and 180°) for the crystal and each exposure of 30 s covered 0.3° in ω. The crystal-to-detector distance was 5 cm and the detector swing angle was -35°. Crystal decay was monitored by repeating 50 initial frames at the end of data collection and analysing the intensity of duplicate reflections, and was found to be negligible. |
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 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 > σ(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 | ||
Br1 | 0.01467 (2) | 0.17658 (4) | 0.02239 (7) | 0.0871 (2) | |
Cl1 | 0.38225 (4) | 0.06873 (6) | 0.14071 (12) | 0.0535 (3) | |
N1 | 0.25402 (12) | −0.13389 (18) | 0.5294 (3) | 0.0341 (6) | |
O1 | 0.24139 (12) | 0.03406 (17) | 0.6532 (3) | 0.0555 (6) | |
O2 | 0.38958 (11) | 0.06516 (17) | 0.5772 (3) | 0.0501 (6) | |
O3 | 0.18197 (14) | −0.2778 (2) | 0.5427 (4) | 0.0783 (8) | |
C1 | 0.27250 (16) | −0.0274 (2) | 0.5641 (4) | 0.0353 (7) | |
C2 | 0.31508 (15) | −0.1864 (2) | 0.4589 (4) | 0.0335 (7) | |
C3 | 0.32712 (18) | −0.2932 (2) | 0.4324 (4) | 0.0431 (8) | |
H3 | 0.2920 | −0.3436 | 0.4517 | 0.052* | |
C4 | 0.3933 (2) | −0.3223 (3) | 0.3762 (4) | 0.0489 (9) | |
H4 | 0.4025 | −0.3938 | 0.3572 | 0.059* | |
C5 | 0.44571 (19) | −0.2491 (3) | 0.3476 (4) | 0.0508 (9) | |
H5 | 0.4897 | −0.2716 | 0.3099 | 0.061* | |
C6 | 0.43368 (16) | −0.1421 (3) | 0.3744 (4) | 0.0436 (8) | |
H6 | 0.4692 | −0.0921 | 0.3559 | 0.052* | |
C7 | 0.36768 (14) | −0.1113 (2) | 0.4291 (4) | 0.0338 (7) | |
C8 | 0.34101 (15) | −0.0042 (2) | 0.4713 (4) | 0.0355 (7) | |
C9 | 0.32712 (15) | 0.0872 (2) | 0.3264 (4) | 0.0354 (7) | |
C10 | 0.36599 (17) | 0.1576 (2) | 0.4714 (5) | 0.0516 (9) | |
H10A | 0.4055 | 0.1981 | 0.4286 | 0.062* | |
H10B | 0.3336 | 0.2036 | 0.5314 | 0.062* | |
C11 | 0.25103 (15) | 0.1110 (2) | 0.2527 (4) | 0.0354 (7) | |
C12 | 0.22197 (17) | 0.2117 (2) | 0.2610 (4) | 0.0425 (8) | |
H12 | 0.2497 | 0.2664 | 0.3142 | 0.051* | |
C13 | 0.15194 (18) | 0.2320 (3) | 0.1910 (5) | 0.0534 (9) | |
H13 | 0.1329 | 0.3002 | 0.1950 | 0.064* | |
C14 | 0.11113 (17) | 0.1500 (3) | 0.1158 (5) | 0.0504 (9) | |
C15 | 0.13853 (18) | 0.0483 (3) | 0.1064 (5) | 0.0537 (9) | |
H15 | 0.1102 | −0.0065 | 0.0557 | 0.064* | |
C16 | 0.20849 (17) | 0.0300 (3) | 0.1736 (5) | 0.0471 (8) | |
H16 | 0.2278 | −0.0378 | 0.1662 | 0.057* | |
C17 | 0.18800 (18) | −0.1837 (3) | 0.5626 (5) | 0.0516 (9) | |
C18 | 0.12870 (19) | −0.1140 (3) | 0.6140 (7) | 0.0818 (13) | |
H18A | 0.1190 | −0.0606 | 0.5235 | 0.123* | |
H18B | 0.1427 | −0.0805 | 0.7269 | 0.123* | |
H18C | 0.0860 | −0.1557 | 0.6249 | 0.123* |
U11 | U22 | U33 | U12 | U13 | U23 | |
Br1 | 0.0510 (3) | 0.1050 (4) | 0.1027 (4) | 0.0141 (2) | −0.0112 (2) | 0.0170 (3) |
Cl1 | 0.0560 (5) | 0.0370 (5) | 0.0711 (6) | −0.0002 (4) | 0.0275 (4) | 0.0051 (4) |
N1 | 0.0326 (13) | 0.0255 (14) | 0.0441 (15) | −0.0047 (10) | 0.0028 (11) | 0.0020 (11) |
O1 | 0.0603 (15) | 0.0355 (13) | 0.0737 (17) | 0.0005 (11) | 0.0230 (13) | −0.0104 (12) |
O2 | 0.0469 (13) | 0.0430 (14) | 0.0586 (14) | −0.0111 (10) | −0.0074 (10) | −0.0124 (12) |
O3 | 0.0686 (18) | 0.0375 (16) | 0.131 (2) | −0.0204 (13) | 0.0196 (16) | 0.0006 (16) |
C1 | 0.0385 (16) | 0.0250 (16) | 0.0415 (18) | 0.0022 (13) | −0.0012 (13) | 0.0002 (14) |
C2 | 0.0369 (16) | 0.0275 (16) | 0.0347 (16) | 0.0036 (12) | −0.0050 (13) | 0.0016 (13) |
C3 | 0.060 (2) | 0.0280 (18) | 0.0402 (18) | 0.0028 (15) | −0.0041 (15) | 0.0004 (14) |
C4 | 0.073 (3) | 0.0323 (19) | 0.0401 (19) | 0.0185 (17) | −0.0041 (17) | −0.0001 (15) |
C5 | 0.051 (2) | 0.057 (2) | 0.0434 (19) | 0.0285 (18) | −0.0014 (15) | −0.0016 (17) |
C6 | 0.0347 (17) | 0.053 (2) | 0.0417 (18) | 0.0040 (15) | −0.0035 (14) | 0.0020 (16) |
C7 | 0.0321 (15) | 0.0313 (17) | 0.0367 (16) | 0.0029 (12) | −0.0055 (12) | 0.0007 (13) |
C8 | 0.0313 (16) | 0.0287 (17) | 0.0457 (18) | −0.0060 (12) | −0.0011 (13) | −0.0068 (14) |
C9 | 0.0345 (16) | 0.0215 (16) | 0.0512 (19) | −0.0033 (12) | 0.0103 (13) | −0.0054 (13) |
C10 | 0.0425 (19) | 0.0313 (19) | 0.081 (3) | −0.0118 (14) | 0.0027 (17) | −0.0172 (18) |
C11 | 0.0402 (16) | 0.0214 (15) | 0.0454 (18) | 0.0001 (13) | 0.0082 (13) | 0.0028 (13) |
C12 | 0.0495 (19) | 0.0242 (17) | 0.054 (2) | −0.0021 (14) | 0.0073 (15) | 0.0013 (15) |
C13 | 0.056 (2) | 0.0331 (19) | 0.072 (2) | 0.0101 (16) | 0.0122 (18) | 0.0103 (18) |
C14 | 0.0401 (18) | 0.057 (2) | 0.054 (2) | 0.0056 (16) | −0.0005 (15) | 0.0129 (18) |
C15 | 0.051 (2) | 0.046 (2) | 0.062 (2) | −0.0065 (17) | −0.0089 (17) | −0.0049 (18) |
C16 | 0.0490 (19) | 0.0289 (18) | 0.062 (2) | 0.0031 (15) | −0.0023 (16) | −0.0029 (16) |
C17 | 0.046 (2) | 0.044 (2) | 0.066 (2) | −0.0104 (16) | 0.0084 (17) | 0.0072 (18) |
C18 | 0.042 (2) | 0.066 (3) | 0.140 (4) | −0.0086 (19) | 0.025 (2) | −0.006 (3) |
Br1—C14 | 1.900 (3) | C7—C8 | 1.479 (4) |
Cl1—C9 | 1.805 (3) | C8—C9 | 1.587 (4) |
N1—C1 | 1.403 (4) | C9—C11 | 1.505 (4) |
N1—C17 | 1.418 (4) | C9—C10 | 1.535 (4) |
N1—C2 | 1.448 (4) | C10—H10A | 0.9700 |
O1—C1 | 1.200 (3) | C10—H10B | 0.9700 |
O2—C8 | 1.445 (3) | C11—C12 | 1.380 (4) |
O2—C10 | 1.455 (4) | C11—C16 | 1.392 (4) |
O3—C17 | 1.198 (4) | C12—C13 | 1.386 (4) |
C1—C8 | 1.526 (4) | C12—H12 | 0.9300 |
C2—C3 | 1.380 (4) | C13—C14 | 1.374 (5) |
C2—C7 | 1.390 (4) | C13—H13 | 0.9300 |
C3—C4 | 1.380 (4) | C14—C15 | 1.382 (5) |
C3—H3 | 0.9300 | C15—C16 | 1.375 (4) |
C4—C5 | 1.370 (5) | C15—H15 | 0.9300 |
C4—H4 | 0.9300 | C16—H16 | 0.9300 |
C5—C6 | 1.383 (4) | C17—C18 | 1.484 (5) |
C5—H5 | 0.9300 | C18—H18A | 0.9600 |
C6—C7 | 1.379 (4) | C18—H18B | 0.9600 |
C6—H6 | 0.9300 | C18—H18C | 0.9600 |
C1—N1—C17 | 126.4 (3) | C10—C9—Cl1 | 110.7 (2) |
C1—N1—C2 | 108.4 (2) | C8—C9—Cl1 | 111.10 (18) |
C17—N1—C2 | 125.2 (2) | O2—C10—C9 | 91.4 (2) |
C8—O2—C10 | 92.2 (2) | O2—C10—H10A | 113.4 |
O1—C1—N1 | 126.7 (3) | C9—C10—H10A | 113.4 |
O1—C1—C8 | 125.9 (3) | O2—C10—H10B | 113.4 |
N1—C1—C8 | 107.4 (2) | C9—C10—H10B | 113.4 |
C3—C2—C7 | 121.0 (3) | H10A—C10—H10B | 110.7 |
C3—C2—N1 | 129.6 (3) | C12—C11—C16 | 118.7 (3) |
C7—C2—N1 | 109.2 (2) | C12—C11—C9 | 121.7 (3) |
C4—C3—C2 | 117.5 (3) | C16—C11—C9 | 119.5 (2) |
C4—C3—H3 | 121.3 | C11—C12—C13 | 120.7 (3) |
C2—C3—H3 | 121.3 | C11—C12—H12 | 119.6 |
C5—C4—C3 | 122.1 (3) | C13—C12—H12 | 119.6 |
C5—C4—H4 | 119.0 | C14—C13—C12 | 119.1 (3) |
C3—C4—H4 | 119.0 | C14—C13—H13 | 120.5 |
C4—C5—C6 | 120.5 (3) | C12—C13—H13 | 120.5 |
C4—C5—H5 | 119.8 | C13—C14—C15 | 121.6 (3) |
C6—C5—H5 | 119.8 | C13—C14—Br1 | 119.4 (3) |
C7—C6—C5 | 118.3 (3) | C15—C14—Br1 | 119.0 (3) |
C7—C6—H6 | 120.8 | C16—C15—C14 | 118.6 (3) |
C5—C6—H6 | 120.8 | C16—C15—H15 | 120.7 |
C6—C7—C2 | 120.7 (3) | C14—C15—H15 | 120.7 |
C6—C7—C8 | 129.8 (3) | C15—C16—C11 | 121.3 (3) |
C2—C7—C8 | 109.5 (2) | C15—C16—H16 | 119.3 |
O2—C8—C7 | 117.6 (2) | C11—C16—H16 | 119.3 |
O2—C8—C1 | 111.9 (2) | O3—C17—N1 | 119.3 (3) |
C7—C8—C1 | 103.2 (2) | O3—C17—C18 | 123.6 (3) |
O2—C8—C9 | 89.71 (19) | N1—C17—C18 | 117.0 (3) |
C7—C8—C9 | 123.7 (3) | C17—C18—H18A | 109.5 |
C1—C8—C9 | 110.7 (2) | C17—C18—H18B | 109.5 |
C11—C9—C10 | 121.1 (2) | H18A—C18—H18B | 109.5 |
C11—C9—C8 | 119.4 (2) | C17—C18—H18C | 109.5 |
C10—C9—C8 | 84.1 (2) | H18A—C18—H18C | 109.5 |
C11—C9—Cl1 | 108.6 (2) | H18B—C18—H18C | 109.5 |
C17—N1—C1—O1 | 13.2 (5) | O2—C8—C9—C11 | −134.3 (2) |
C2—N1—C1—O1 | −164.8 (3) | C7—C8—C9—C11 | 102.2 (3) |
C17—N1—C1—C8 | −168.2 (3) | C1—C8—C9—C11 | −20.8 (3) |
C2—N1—C1—C8 | 13.8 (3) | O2—C8—C9—C10 | −11.7 (2) |
C1—N1—C2—C3 | 168.4 (3) | C7—C8—C9—C10 | −135.3 (3) |
C17—N1—C2—C3 | −9.6 (5) | C1—C8—C9—C10 | 101.7 (3) |
C1—N1—C2—C7 | −7.1 (3) | O2—C8—C9—Cl1 | 98.2 (2) |
C17—N1—C2—C7 | 174.8 (3) | C7—C8—C9—Cl1 | −25.4 (3) |
C7—C2—C3—C4 | 0.3 (4) | C1—C8—C9—Cl1 | −148.4 (2) |
N1—C2—C3—C4 | −174.8 (3) | C8—O2—C10—C9 | −12.7 (2) |
C2—C3—C4—C5 | 0.2 (5) | C11—C9—C10—O2 | 132.5 (3) |
C3—C4—C5—C6 | −0.1 (5) | C8—C9—C10—O2 | 11.6 (2) |
C4—C5—C6—C7 | −0.4 (5) | Cl1—C9—C10—O2 | −98.7 (2) |
C5—C6—C7—C2 | 0.9 (4) | C10—C9—C11—C12 | 22.9 (4) |
C5—C6—C7—C8 | 178.5 (3) | C8—C9—C11—C12 | 124.5 (3) |
C3—C2—C7—C6 | −0.8 (4) | Cl1—C9—C11—C12 | −106.8 (3) |
N1—C2—C7—C6 | 175.2 (2) | C10—C9—C11—C16 | −157.2 (3) |
C3—C2—C7—C8 | −178.8 (3) | C8—C9—C11—C16 | −55.6 (4) |
N1—C2—C7—C8 | −2.8 (3) | Cl1—C9—C11—C16 | 73.1 (3) |
C10—O2—C8—C7 | 140.8 (3) | C16—C11—C12—C13 | −0.4 (4) |
C10—O2—C8—C1 | −99.9 (3) | C9—C11—C12—C13 | 179.5 (3) |
C10—O2—C8—C9 | 12.3 (2) | C11—C12—C13—C14 | 1.2 (5) |
C6—C7—C8—O2 | −43.4 (4) | C12—C13—C14—C15 | −0.8 (5) |
C2—C7—C8—O2 | 134.4 (3) | C12—C13—C14—Br1 | 179.2 (2) |
C6—C7—C8—C1 | −167.1 (3) | C13—C14—C15—C16 | −0.3 (5) |
C2—C7—C8—C1 | 10.7 (3) | Br1—C14—C15—C16 | 179.7 (3) |
C6—C7—C8—C9 | 66.6 (4) | C14—C15—C16—C11 | 1.1 (5) |
C2—C7—C8—C9 | −115.6 (3) | C12—C11—C16—C15 | −0.8 (5) |
O1—C1—C8—O2 | 36.3 (4) | C9—C11—C16—C15 | 179.3 (3) |
N1—C1—C8—O2 | −142.3 (2) | C1—N1—C17—O3 | −172.8 (3) |
O1—C1—C8—C7 | 163.7 (3) | C2—N1—C17—O3 | 4.9 (5) |
N1—C1—C8—C7 | −14.9 (3) | C1—N1—C17—C18 | 9.5 (5) |
O1—C1—C8—C9 | −62.1 (4) | C2—N1—C17—C18 | −172.8 (3) |
N1—C1—C8—C9 | 119.3 (2) |
Experimental details
Crystal data | |
Chemical formula | C18H13BrClNO3 |
Mr | 406.65 |
Crystal system, space group | Monoclinic, P21/c |
Temperature (K) | 233 |
a, b, c (Å) | 18.5810 (5), 12.5906 (4), 7.4709 (2) |
β (°) | 94.645 (1) |
V (Å3) | 1742.05 (9) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 2.53 |
Crystal size (mm) | 0.36 × 0.28 × 0.16 |
Data collection | |
Diffractometer | Siemens SMART CCD area-detector diffractometer |
Absorption correction | Empirical (using intensity measurements) (SADABS; Sheldrick, 1996) |
Tmin, Tmax | 0.463, 0.688 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 10113, 4173, 2016 |
Rint | 0.080 |
(sin θ/λ)max (Å−1) | 0.666 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.050, 0.120, 0.81 |
No. of reflections | 4173 |
No. of parameters | 219 |
H-atom treatment | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 0.45, −0.76 |
Computer programs: SMART (Siemens, 1996), SAINT (Siemens, 1996), SAINT, SHELXTL (Sheldrick, 1997), SHELXTL, PARST (Nardelli, 1995) and PLATON (Spek, 1990).
Br1—C14 | 1.900 (3) | C8—C9 | 1.587 (4) |
Cl1—C9 | 1.805 (3) | C9—C11 | 1.505 (4) |
C1—C8 | 1.526 (4) | C9—C10 | 1.535 (4) |
C7—C8 | 1.479 (4) |
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The compound 1-acetylisatin undergoes photoinduced cycloaddition reactions with a wide range of alkenes. These reactions have become one of the synthetic routes to obtain the corresponding spiroxetane derivatives (Xue et al., 2001; Zhang et al., 2002). The asymmetric alkenes in these reactions give syn- and anticlinal spiroxetanes as a separable mixture by column chromatography. The structure analyses of the spiroxetanes have also been reported by us in previous studies (Usman et al., 2001, 2002). As an extension of our systematic study into these photoinduced reactions, we have isolated the title compound, (I), which was one of the spiroxetanes resulting from such a photoinduced reaction of 1-acetylisatin with β-chloro-4-bromostyrene. An X-ray crystal structure analysis has been undertaken to elucidate its steric configuration and conformation, and the results are presented here. \sch
The bond lengths and angles in (I) (Fig. 1) are within normal ranges (Allen et al., 1987). The C8—C9 bond length of the spiroxetane (C8/C9/C10/O2) is slightly longer than the typical value for Csp3—Csp3 due to the bulky substituents attached to both atoms C8 and C9. The spiroxetane is out of planarity, with atoms O2, C8, C9, and C10 deviating by 0.085 (2), -0.078 (3), 0.074 (3), and -0.080 (3) Å, respectively, from its mean plane, and the dihedral angle between the O2/C8/C10 and C8/C9/C10 planes is 163.0 (3)°.
The orientations of the indole (C1/N1/C2—C8), bromophenyl (C11—C16/Br1) and chloro (Cl1) substituents are conditioned by the Csp3 state of atoms C8 and C9, while the relative distribution of the indole and bromophenyl substituents is determined by the torsion angles of C7—C8—C9—Cl1 - 25.4 (1)° and C1—C8—C9—C11 - 20.8 (3). These indicate the staggered configuration of atoms C8 and C9 joining the two subtituents. The bond angles subtended at atoms C8 and C9 are in the ranges 89.7 (2)–123.7 (3)° and 84.1 (2)–121.1 (2)°, respectively. The oxetane ring and the indole moiety are approximately orthogonal, corresponding to an angle of 81.1 (2)° between their mean planes, and the planar bromophenyl substituent makes a dihedral angle of 42.9 (2)° with respect to the mean plane of the oxetane ring.
The indole moiety is out of planarity, with the heterocyclic ring being distorted from planarity towards an envelope conformation. Atom C1 is displaced by 0.216 (3) Å from the N1/C2/C7/C8 plane, and the ketone atom O1 attached to C1 deviates by 0.331 (2) Å from the mean plane of the heterocyclic ring. The mean plane of the heterocyclic ring makes an angle of 7.1 (2)° with the benzene ring (C2—C7).
In (I), the acetyl group (O3/C17/C18) attached at N1 is twisted by an angle of 5.1 (1)° from the mean plane of the indole moiety. This indicates that the acetyl group tends to be coplanar with the indole moiety, as usually observed in 1-acetylindole (Usman et al., 2002), due to the interactions of the π-conjugation of the acetyl group. The intramolecular C3—H3···O3 interaction (Table 2), which forms a six-membered closed ring, O3/C17/N1/C2/C3/H3, also participates in the π-conjugation.
As seen in Fig. 1, atom C8 is the S chiral centre and atom C9 is the R chiral centre. However, the centrosymmetric crystal space group indicates that the photoinduced cycloaddition reaction of both achiral 1-acetylisatin and β-chloro-4-bromostyrene gives the racemate spiroxetane mixture of (I).
The molecules of (I) are packed into columns along the b direction (Fig. 2). There are weak intermolecular π···π interactions observed in the crystal, involving the centroid of the benzene ring of the indole moiety. The π···πi [symmetry code: (i) x, -1/2 - y, z - 1/2] and π···πii [symmetry code: (ii) x, -1/2 - y, 1/2 + z] distances are 3.825 (5) Å for both interactions, and the perpendicular distances are 3.392 (5) and 3.535 (5) Å, respectively.