3,7-Dibromohinokitiol: a redetermination

The structure of the title compound (systematic name: 3,7-di­bromo-2-hydroxy-6-iso­propyl­cyclo­hepta-2,4,6-trien-1-one), C₁₀H₁₀Br₂O₂, previously described by Ito, Fukazawa & Iitaka [Tetrahedron Lett. (1972), 13, 745–749], has been redetermined. Strong inter- and intramolecular hydrogen bonds, with H...O distances of 2.17 (9) and 2.06 (6) Å, respectively, are observed. There are also two short Br...Br and two short Br...(ring centroid) interactions. Important dimensions include C—O(carbonyl) = 1.252 (5) Å, C—O(hydroxyl) = 1.355 (5) Å, C—Br(3-position) = 1.904 (4) Å and C—Br(7-­position) = 1.905 (4) Å, and an O—C—C—O ring torsion angle of −6.7 (6)°.

S1. Comment

We are interested in the chemical behaviour of troponoid compounds in rhodium(I) complexes (Steyl et al., 2001; Roodt et al., 2003), and have therefore synthesized the title compound, (I), by means of direct bromination of hinokitiol in an aqueous medium. Although the structure of (I) has been reported previously (Ito et al., 1972), limited data were available, and so a new data set was collected to obtain a more accurate structure. \sch

The molecular structure of (I) is shown in Fig. 1, with the associated dimensions given in Table 1. A clear bond pattern is observed for the troponoid ring system, with the C2—C3 [1.355 (6) Å] and C4—C5 [1.369 (6) Å] distances tending towards the standard C—C double-bond length (1.34 Å). The remaining bonds between the atoms in the seven-membered ring fall well within the range observed in benzene for delocalized C—C bonds (C≐C 1.44 Å). Furthermore, the C5—C6—C7—C1 torsion angle of 0.3 (8)° indicates a planar delocalized π–π system, as expected for standard troponoid compounds. High anisotropy is observed for atom C10, which lies on the periphery of the molecule, and this is considered to be a result of weak packing forces, allowing for high flexibility of the propyl moeity.

The crystal packing in (I) involves several different types of secondary interaction. An intermolecular O2—H2···O1 hydrogen bond connects molecules to form inversion-symmetric dimers (Fig. 2 and Table 2). The distance between the planes through the cycloheptatriene rings in the dimeric unit is 0.65 (1) Å. A further intermolecular interaction is observed for C9—H9B···Br7. Intramolecular hydrogen bonding occurs via O2—H2···O1 and C8—H8···Br7 (Table 2). A short Br—Br interaction of 3.616 (1) Å is observed between atoms Br3 and Br7(1/2 − x, y − 1/2, z), with a weaker interaction of 3.826 (1) Å between atoms Br3(1 − x, 1 − y, 1 − z) and Br7(1 − x, 1/2 + y, 1/2 − z) (Fig. 2). Finally, there are two aromatic-Br interactions between Br atoms and the cycloheptatriene (C1—C7) ring system. In this first of these, there is a short distance between atom Br3(1/2 + x, y, 1/2 − z) and the plane of the C1—C7 ring [3.727 (2) Å, with individual Br3···C distances ranging from 3.817 (4) to 4.405 (5) Å]. Thus, atom Br3 actually lies nearer to the centroid of the troponoid ring than to any individual atom. Secondly, there is an interaction between atom Br7 and the same plane at (1/2 + x, y, 1/2 − z) [3.515 (3) Å, with individual Br7···C distances ranging from 3.639 (4) to 4.962 (4) Å] (Fig. 2). The latter is in good agreement with observed bromine interactions with benzene and toluene (Vasilyev et al., 2002).

The molecule of (I) has a somewhat distorted ring system, as expressed by the O1—C1—C2—O2 torsion angle of −6.7 (6)°. This is in contrast to other α-diketonates, which tend to be more planar in the solid state, e.g. the parent compound hinokitiol (Derry & Hamor, 1972; Ohishi et al., 1994; Tanaka et al., 2001), which has maximum absolute torsion angles of only ± 2°. In the previous study (Ito et al., 1972), the distortion of the cycloheptatriene system was attributed to steric effects. This raised the question of whether the distortion was induced by packing. The geometry of (I) was thus optimized using PCGAMESS (Granovsky, 2003; Schmidt et al., 1993) with no restraints and characterized as a minimum from the vibrational analysis. The calculated structure is in good agreement with the conformation observed in the crystallographic study (r.m.s. overlay 0.19 Å for the overall structure) (Table 3). In contrast with the observed torsion angle, the calculated O1—C1—C2—O2 torsion angle was only −0.3°, which indeed suggests significant distortion in the solid-state structure due to packing effects. Of additional interest is the fact that the C5—C6—C7—C1 torsion angle of −4.1° in the calculated structure correlates well with those in known hinokitiol compounds (Derry & Hamor, 1972; Ohishi et al., 1994; Tanaka et al., 2001), with a maximum value of ± 5°.

S2. Experimental

Hinokitiol (2-hydroxy-4-isopropyl-2,4,6-cycloheptatrien-1-one, C₁₀O₂H₁₂) (0.134 g, 0.816 mmol) was suspended in water (ca 2 ml) and treated with aqueous bromine solution (ca 4 ml), and the light-yellow product precipitated immediately. The aqueous bromine solution was prepared by dissolving bromine (2 ml) in potassium bromide (7.5 g, 0.063 mol) solution in water (50 ml). Compound (I) was recrystallized from 4 ml me thanol (yield 0.2 g, 76%). Spectroscopic data: ¹H NMR (CDCl₃, 300 MHz, δ, p.p.m.): 1.27 (d, 6H), 3.95 (m, 1H), 6.79 (d, 1H), 7.79 (d, 1H), 10.05 (s, 1H).

S3. Refinement

Computational details: 6–31G**/MP2; effective core potentials were used for all heavy atoms. Optimized structure total energy −118.05775 a.u.; MP2/total energy −120.04197 a.u. Please provide SI equivalent of these energy units. All energies were corrected and ZPE scaled by 0.97. µ = 5.35842 Debye. The coordinates of the hydroxy H atom were refined freely, but its U value was fixed at 1.5U_eq of the parent atom. All other H atoms were positioned geometrically with C—H distances in the range 0.93–0.98 Å Is this correct? and allowed to ride on their parent atoms, with U_iso(H) = 1.2U_eq of the parent atom.

Computing details

Data collection: SMART-NT (Bruker, 1998); cell refinement: SAINT-Plus (Bruker, 1999); data reduction: SAINT-Plus and XPREP (Bruker, 1999); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: DIAMOND (Brandenburg, 2000); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. The molecular structure of (I), showing the atom-numbering scheme and with displacement ellipsoids at the 30% probability level.
	Fig. 2. Part of the unit cell of (I), showing the intra- and intermolecular hydrogen bonding [symmetry codes: (i) 1 − x, 1 − y, 1 − z; (ii) x, 1/2 − y, z − 1/2; (iii) 1/2 − x, 1/2 + y, z].

3,7-dibromo-2-hydroxy-6-isopropyl-2,4,6-cycloheptatrien-1-one

Crystal data

C10H10Br2O2	Dx = 1.942 Mg m^−3 Dm = 1.94 Mg m^−3 Dm measured by flotation in aqueous KI
Mr = 322.00	Melting point: 133 K
Orthorhombic, Pbca	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -p 2ac 2ab	Cell parameters from 1015 reflections
a = 11.138 (2) Å	θ = 2.8–24.4°
b = 13.570 (3) Å	µ = 7.33 mm^−1
c = 14.570 (3) Å	T = 293 K
V = 2202.3 (8) Å^3	Parallelepiped, orange
Z = 8	0.35 × 0.17 × 0.16 mm
F(000) = 1248

Data collection

Make? Model? CCD area-detector diffractometer	2080 independent reflections
Radiation source: fine-focus sealed tube	1313 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.046
Detector resolution: 512 x 512 pixels mm^-1	θmax = 25.7°, θmin = 5.2°
ω scans	h = −11→13
Absorption correction: empirical (using intensity measurements) (SADABS; Sheldrick, 1996)	k = −14→16
Tmin = 0.170, Tmax = 0.309	l = −17→17
11457 measured reflections

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.037	Hydrogen site location: riding model
wR(F^2) = 0.106	H-atom parameters constrained
S = 1.01	w = 1/[σ^2(Fo^2) + (0.0587P)^2] where P = (Fo^2 + 2Fc^2)/3
2080 reflections	(Δ/σ)max < 0.001
131 parameters	Δρmax = 0.60 e Å^−3
0 restraints	Δρmin = −0.70 e Å^−3

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 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Br7	0.60519 (5)	0.28836 (4)	0.30348 (4)	0.0604 (2)
Br3	0.15095 (5)	0.62456 (4)	0.30105 (4)	0.0592 (2)
O2	0.3374 (3)	0.5565 (3)	0.4254 (2)	0.0557 (10)
H2	0.391 (5)	0.548 (5)	0.464 (4)	0.084*
O1	0.5205 (3)	0.4465 (2)	0.4124 (2)	0.0550 (9)
C6	0.4460 (4)	0.3779 (3)	0.1767 (3)	0.0406 (11)
C1	0.4591 (4)	0.4479 (3)	0.3405 (3)	0.0374 (10)
C8	0.4958 (5)	0.3019 (3)	0.1084 (3)	0.0540 (13)
H8	0.5362	0.2506	0.1444	0.065*
C3	0.2815 (4)	0.5395 (3)	0.2722 (3)	0.0393 (10)
C4	0.2878 (5)	0.5125 (3)	0.1798 (3)	0.0474 (13)
H4	0.2357	0.5456	0.1406	0.057*
C5	0.3605 (4)	0.4439 (4)	0.1391 (3)	0.0472 (12)
H5	0.3525	0.4398	0.0757	0.057*
C2	0.3561 (4)	0.5149 (3)	0.3420 (3)	0.0394 (11)
C7	0.4876 (4)	0.3820 (3)	0.2659 (3)	0.0360 (10)
C9	0.4008 (6)	0.2516 (4)	0.0513 (4)	0.0691 (16)
H9B	0.3441	0.2197	0.0910	0.104*
H9A	0.4379	0.2035	0.0122	0.104*
H9C	0.3601	0.2998	0.0144	0.104*
C10	0.5910 (6)	0.3505 (6)	0.0482 (5)	0.110 (3)
H10A	0.6492	0.3828	0.0864	0.164*
H10C	0.5535	0.3981	0.0088	0.164*
H10B	0.6301	0.3012	0.0116	0.164*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Br7	0.0608 (4)	0.0574 (4)	0.0631 (4)	0.0144 (3)	−0.0172 (3)	−0.0059 (3)
Br3	0.0546 (4)	0.0563 (3)	0.0667 (4)	0.0143 (2)	0.0017 (3)	−0.0055 (3)
O2	0.060 (2)	0.068 (2)	0.039 (2)	0.0088 (19)	0.0000 (16)	−0.0139 (18)
O1	0.062 (2)	0.072 (2)	0.0306 (18)	0.0109 (18)	−0.0082 (16)	−0.0098 (16)
C6	0.042 (3)	0.046 (3)	0.034 (3)	−0.005 (2)	0.001 (2)	0.000 (2)
C1	0.039 (3)	0.038 (2)	0.035 (2)	−0.004 (2)	−0.001 (2)	0.000 (2)
C8	0.066 (4)	0.058 (3)	0.038 (3)	0.010 (3)	−0.001 (3)	−0.012 (2)
C3	0.039 (3)	0.036 (2)	0.043 (3)	0.001 (2)	−0.001 (2)	−0.005 (2)
C4	0.055 (3)	0.047 (3)	0.040 (3)	0.003 (2)	−0.013 (2)	0.004 (2)
C5	0.055 (3)	0.057 (3)	0.029 (3)	0.004 (3)	−0.007 (2)	−0.002 (2)
C2	0.046 (3)	0.039 (3)	0.033 (2)	−0.005 (2)	0.007 (2)	−0.005 (2)
C7	0.036 (3)	0.034 (2)	0.038 (2)	−0.0047 (19)	0.001 (2)	0.003 (2)
C9	0.087 (5)	0.068 (4)	0.052 (3)	−0.007 (3)	0.003 (3)	−0.017 (3)
C10	0.084 (5)	0.130 (6)	0.114 (6)	−0.031 (4)	0.057 (5)	−0.069 (5)

Geometric parameters (Å, º)

Br7—C7	1.905 (4)	C8—H8	0.9800
Br3—C3	1.904 (4)	C3—C2	1.355 (6)
O2—C2	1.355 (5)	C3—C4	1.397 (6)
O2—H2	0.83 (6)	C4—C5	1.369 (6)
O1—C1	1.252 (5)	C4—H4	0.9300
C6—C7	1.380 (6)	C5—H5	0.9300
C6—C5	1.417 (6)	C9—H9B	0.9600
C6—C8	1.537 (6)	C9—H9A	0.9600
C1—C7	1.444 (6)	C9—H9C	0.9600
C1—C2	1.464 (6)	C10—H10A	0.9600
C8—C9	1.509 (7)	C10—H10C	0.9600
C8—C10	1.526 (8)	C10—H10B	0.9600
C2—O2—H2	116 (5)	C4—C5—H5	114.4
C7—C6—C5	124.3 (4)	C6—C5—H5	114.4
C7—C6—C8	121.0 (4)	C3—C2—O2	118.4 (4)
C5—C6—C8	114.6 (4)	C3—C2—C1	128.4 (4)
O1—C1—C7	120.1 (4)	O2—C2—C1	113.1 (4)
O1—C1—C2	115.2 (4)	C6—C7—C1	131.3 (4)
C7—C1—C2	124.7 (4)	C6—C7—Br7	118.3 (3)
C9—C8—C10	111.4 (5)	C1—C7—Br7	110.4 (3)
C9—C8—C6	114.0 (4)	C8—C9—H9B	109.5
C10—C8—C6	109.4 (4)	C8—C9—H9A	109.5
C9—C8—H8	107.2	H9B—C9—H9A	109.5
C10—C8—H8	107.2	C8—C9—H9C	109.5
C6—C8—H8	107.2	H9B—C9—H9C	109.5
C2—C3—C4	128.9 (4)	H9A—C9—H9C	109.5
C2—C3—Br3	116.8 (3)	C8—C10—H10A	109.5
C4—C3—Br3	114.2 (3)	C8—C10—H10C	109.5
C5—C4—C3	128.7 (4)	H10A—C10—H10C	109.5
C5—C4—H4	115.7	C8—C10—H10B	109.5
C3—C4—H4	115.7	H10A—C10—H10B	109.5
C4—C5—C6	131.3 (4)	H10C—C10—H10B	109.5
C7—C6—C8—C9	136.0 (5)	O1—C1—C2—C3	172.7 (4)
C5—C6—C8—C9	−46.8 (6)	C7—C1—C2—C3	−11.2 (7)
C7—C6—C8—C10	−98.5 (6)	O1—C1—C2—O2	−6.7 (6)
C5—C6—C8—C10	78.7 (6)	C7—C1—C2—O2	169.4 (4)
C2—C3—C4—C5	10.2 (9)	C5—C6—C7—C1	0.3 (8)
Br3—C3—C4—C5	−171.3 (4)	C8—C6—C7—C1	177.2 (4)
C3—C4—C5—C6	2.8 (9)	C5—C6—C7—Br7	−178.7 (4)
C7—C6—C5—C4	−11.4 (8)	C8—C6—C7—Br7	−1.8 (6)
C8—C6—C5—C4	171.5 (5)	O1—C1—C7—C6	−169.9 (5)
C4—C3—C2—O2	174.7 (5)	C2—C1—C7—C6	14.2 (7)
Br3—C3—C2—O2	−3.8 (6)	O1—C1—C7—Br7	9.2 (5)
C4—C3—C2—C1	−4.6 (8)	C2—C1—C7—Br7	−166.8 (3)
Br3—C3—C2—C1	176.9 (4)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O2—H2···O1	0.83 (6)	2.17 (9)	2.530 (5)	110 (5)
O2—H2···O1^i	0.83 (6)	2.06 (6)	2.845 (5)	159 (6)
C8—H8···Br7	0.98	2.50	3.097 (5)	119
C9—H9B···Br7^ii	0.96	3.21	3.946 (5)	135

Symmetry codes: (i) −x+1, −y+1, −z+1; (ii) x−1/2, y, −z+1/2.