Two similar dibenzo cyclic ethers with dissimilar conformations

Two dibenzo cyclic ether compounds, 6,12-dibromo­di­ben­zo[d,i]-1,2,3,6,7,8-hexa­hydro-1,3-dioxecin (systematic name: 8,16-dibromo-2,4-dioxatricyclo[12.4.0.0^5,10]octadeca-5,7,9,14,16,18-hexaene), C₁₆H₁₄Br₂O₂, (II), and 8,14-dibromodibenzo[f,k]-1,5-dioxa-1,2,3,4,5,8,9,10-octa­hydrocyclo­dodecene (systematic name: 7,19-dibromo-11,15-dioxatricyclo[14.4.0.0^5,10]icosa-5,7,9,16,18,20-hexaene), C₁₈H₁₈Br₂O₂, (III), were pre­pared as scaffolding for phosphate-anion receptors. In both compounds, the two aromatic rings are linked by three methyl­ene units ortho to the oxygen substituent of each ring. The only difference between the two compounds is the number of methyl­ene units linking the two ether O atoms. The dibenzo cyclic ether with an ether linkage of one methyl­ene unit adopts a chair-like conformation, where the two aromatic rings are parallel to each other. On the other hand, the dibenzo cyclic ether with an oxygen linkage of three methyl­ene units adopts a bowl-like conformation. The latter scaffold configuration is the only structure of the two that would allow for the placement of convergent functional groups necessary for the establishment of an anion-selective binding pocket.

S1. Comment

The design and fabrication of artificial anion receptors is an area of much current interest (Antonisse & Reinhoudt, 1998; Beer & Gale, 2001; Biaci et al., 1997; Schmidtchen & Berger, 1997; Sessler et al., 2006). This is partly due to the fact that anions are vital to the maintenance of biological systems; the large majority of protein–cofactor, protein–protein, or protein–DNA interactions, for example, involve anions (Sessler et al., 2006). Additionally, because the use of anions in agriculture and other industry has had deleterious environmental impact, the need for environmental sensors or environmental remediation requiring anion receptors has increased. Particularly challenging is the preparation of receptors that exhibit a high degree of discrimination towards specific anions. To accomplish this, a receptor's binding groups must be aligned correctly in its supramolecular matrix so as to differentiate between the three-dimensional shapes (e.g. linear, trigonal, tetrahedral, or spherical) of anions.

Our goal to prepare selective receptors for phosphatidylglycerol, an anionic phospholipid unique to bacterial membranes, dictated the synthesis of a receptor that could bind to the lipid's phosphate anion and the glycerol hydroxyl groups. The scaffold portion of the receptor had to be amenable to chemical modification that would allow for the proper positioning of binding groups during the target molecule's synthetic pathway. Molecular modeling suggested the scaffold should be somewhat concave to best align the phosphate-anion-binding groups with the receptor's functional groups intended to bind to the hydroxyl groups of the glycerol. Results from our previous work suggested that the best way to bind the phosphate anion would be with two functional groups, such as neutral urea groups or charged ammonium groups (Burns et al., 2005; Calderon-Kawasaki et al., 2007; Jagessar et al., 1997, 1998), and modeling suggested the use of two more hydrogen-bonding groups to bind to the hydroxyl moieties. Based on these requirements, the scaffold chosen was bis-phenol 1 (shown in Fig. 1). This structure is readily available in good yield by coupling appropriate Grignard and bis-tosylate reagents with the use of our soluble Cu^I catalyst (Burns et al., 1997, 2000). The ortho positions on the bis-phenol can be elaborated via aromatic electrophilic addition to provide for the anion-binding unit, while the bromine-substituted para positions can be elaborated via organometallic reactions to provide the hydroxyl-binding unit. The phenolic O atoms can be linked to provide a preorganized binding pocket with the newly formed dibenzo cyclic ether. What was not clear a priori was how the length of linkage between the two phenolic O atoms would affect the overall conformation of the molecule. Therefore, two dibenzo cyclic ethers were prepared, (II) and (III) . Molecular modeling suggested that a linkage containing either one methylene or three methylenes would furnish a receptor with an appropriately sized binding pocket.

X-ray crystal structures of the two linked compounds are shown in Fig. 2. (III) displays a concave structure and would act as a good scaffold for the receptor's binding groups. In contrast, the ring in (II) adopts a chair-like conformation, with the two aromatic rings parallel to each other. With the desired concave structure, the macrocycle in (III) could be elaborated with appropriate functional groups that would be aligned correctly in space, and therefore has the potential to furnish a binding pocket that would be phosphate-anion selective. With the chair-like configuration of (II), any anion-binding functional groups would be positioned in opposite directions, precluding the correct alignment of convergent functional groups deemed necessary for selective anion binding.

(II) crystallizes on a general position in the monoclinic space group P2₁/c. The dihedral angle between the two aromatic rings is 11.24 (13)°. The dihedral angles between the aromatic rings and the plane defined by O1, O2, C7 and C9 are 74.38 (7) and 79.08 (7)°. The (CH₂)₃ and OCH₂O chains linking the two aromatic rings essentially mirror each other. (III) crystallizes on a general position in the orthorhombic space group Pbca. In contrast to (II), (III) adopts a concave bowl conformation, with a dihedral angle between the two aromatic rings of 61.67 (12)°, and dihedral angles between the aromatic rings and the mean plane defined by O1, O2, C16 and C18 of 28.92 (11) and 32.76 (11)°. The two O atoms are both directed towards the bottom of the bowl, with an O1···O2 distance of 2.824 (4) Å. The crystal packing in both (II) and (III) shows short Br···Br contacts between the aryl bromide moieties of different molecules (Fig. 3a). Such interactions are recognized as a driving force in crystal packing and have been classified into two types: type A, a linear arrangement with both C—Br···Br angles in the order of 150–180°; and type B, a perpendicular arrangement with one linear C—Br···Br angle and the other C—Br···Br angle close to 90° (Brehmer et al., 2000). In (II), the Br···Br interaction is between inversion-related Br atoms to form dimers. The Br1···Br1ⁱ distance is 3.4322 (4) Å and the C1—Br1···Br1ⁱ angle is 160.59 (8)° [symmetry code (i) = 2 - x, 1 - y, -1 - z], both of which are in the range seen for type A. In (III), the Br···Br interaction is head-to-tail, forming a chain of molecules. The Br1···Br2ⁱ distance is 3.5548 (8) Å, with C1—Br1···Br2ⁱ = 156.93 (13)° [symmetry code (i) = x, 1/2 - y, 1/2 + z] and C13—Br2···Br1ⁱⁱ= 149.64 (14)° [symmetry code (ii) = x, 1/2 - y, z - 1/2] , also within the range for type A. The parameters of the Br···Br interaction in (III) are influenced by a C—H···Br interaction [C2···Br1ⁱⁱⁱ 3.732 (5) Å; symmetry code (iii) = 3/2 - x, 1/2 + y, z] and a π–π interaction (3.44 Å between planes) involving Br2.

The two compounds in this study demonstrate quite clearly the importance of the oxygen linkage in defining the conformation of the macrocycle and in organizing the scaffold for proper alignment of functional groups for selective anion binding. Work is currently underway to further elaborate (II) with the appropriate phosphate-anion-binding functional groups and hydroxyl-binding functional groups necessary for recognition of phosphatidylglycerol.

Related literature

For related literature, see: Antonisse & Reinhoudt (1998); Beer & Gale (2001); Biaci et al. (1997); Brehmer et al. (2000); Burns et al. (1997, 2000, 2005); Calderon-Kawasaki, Kularatne, Li, Noll, Scheidt & Burns (2007); Jagessar & Burns (1997); Jagessar et al. (1998); Schmidtchen & Berger (1997); Sessler et al. (2006).

S2. Experimental

For the synthesis of (II), 1,1'-(1,3-propanediyl)bis(5-bromo-2-methoxybenzene) (1 g, 2.6 mmol), dried under vacuum sitting over anhydrous phosphorous oxide, was transferred along with potassium carbonate (1.1 g, 7.8 mmol) and 18-crown-6 (1 g, 3.8 mmol) into a round-bottom flask under a nitrogen atmosphere. The flask was covered with aluminium foil, and 100 ml of THF distilled from sodium was added to the reaction mixture. Diiodomethane (0.83 ml, 10.3 mmol) was added dropwise to the solution, and the reaction mixture heated to 348 K for 18 h, at which time the reaction was judged to be complete as indicated by TLC. The reaction was then quenched with 1 M HCl and extracted three times with methylene chloride. The combined organic fractions were washed with saturated sodium bicarbonate and brine, dried over sodium sulfate and the solvent was removed under vacuum to give 1.5 g of a solid material. The crude product was recrystallized from hexanes layered upon ethyl acetate to give 0.61 g of crystals. The mother liquor was condensed and subjected to column chromatography, eluting with 35:65 methylene chloride:hexanes, furnishing 0.22 g of crystalline solid, which resulted in an overall yield of 81%; m.p. 450–451 K; ¹H NMR (300 MHz) CDCl₃ δ2.05 (m, 2H), 2.49 (t, 4H, J=6.04 Hz), 5.66 (s, 2H), 6.98 (d, 2H, J=4.21 Hz), 7.32–7.38 (m, 4H); ¹³C NMR (100.5 MHz) CDCl₃ δ24.14, 32.35, 97.66, 117.40, 120.92, 130.64, 133.25,137.27, 154.92. MS m/z 398 (M⁺), 317, 238.

For the synthesis of (III), 1,1'-(1,3-propanediyl)bis(5-bromo-2-methoxybenzene) (0.3 g, 0.8 mmol), dried under vacuum sitting over anhydrous phosphorous oxide, was transferred along with potassium carbonate (0.33 g, 2.4 mmol) and 18-crown-6 (0.32 g, 1.2 mmol) into a dried round-bottom flask under a nitrogen atmosphere. The flask was covered with aluminium foil and 25 ml of THF (distilled from sodium) was added to the reaction mixture. At this time, 1,3-dibromopropane (0.3 ml, 3 mmol) was added dropwise to the solution and the reaction mixture was heated to 348 K for 36 h, at which time the reaction was judged to be complete as indicated by TLC. The reaction was then quenched with 1 M HCl and extracted three times with ethyl acetate. The combined organic fractions were washed with saturated sodium bicarbonate and brine, dried over sodium sulfate and the solvent was removed under vacuum to yield 0.6 g of an oily product. The crude reaction product was subjected to Chromatotron^TM prep TLC (eluted with 10% ethyl acetate–hexane) to yield 0.192 g of a solid which was then recrystallized from ethanol to furnish 0.183 g (55% yield) of X-ray diffraction quality crystals. m.p. 445–446 K; ¹H NMR (300 MHz) CDCl₃ δ1.84–1.94 (m, 2H), 2.23–2.29 (m, 2H), 2.58 (t, 4H, J=7.4 Hz), 4.17 (t, 4H, J=4.84 Hz), 6.67 (d, 2H, J=4.48 Hz), 7.22–7.26 (m, 4H); ¹³C NMR (100 MHz) CDCl₃ δ27.99, 29.90, 31.47, 67.97, 112.45, 129.56, 132.84, 134.18, 156.04. MS m/z 424,425,426 (M⁺).

S3. Refinement

H atoms were inserted at calculated positions and refined with standard SHELXL97 constraints.

Computing details

For both compounds, data collection: APEX2 (Bruker, 2005); cell refinement: APEX2 (Bruker, 2005); data reduction: SAINT (Bruker, 1996); 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).

Figures

	Fig. 1. Modular structure of the bis-phenol receptor. Facile elaboration allows iterative studies of structure–function relationships using different anion- and solvent-binding sites.
	Fig. 2. Displacement ellipsoid drawings (50% probability) of (II) and (III). H atoms have been omitted for clarity.
	Fig. 3. ORTEP drawings of (II) and (III), showing the intermolecular Br···Br and π–π interactions. Symmetry codes: (a) = 2 - x, 1 - y, -1 - z for (II); (a) = x, 1/2 - y, -1/2 + z , b = 2 -x, 1 - y, 1 - z for (III).

(II) 8,16-dibromo-2,4-dioxatricyclo[12.4.0.0^5,10]octadeca-5,7,9,14,16,18-hexaene

Crystal data

C16H14Br2O2	F(000) = 784
Mr = 398.09	Dx = 1.811 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 5967 reflections
a = 21.3204 (5) Å	θ = 3.5–26°
b = 8.8456 (2) Å	µ = 5.55 mm^−1
c = 7.8155 (2) Å	T = 150 K
β = 97.969 (1)°	Block, colorless
V = 1459.70 (6) Å^3	0.25 × 0.18 × 0.14 mm
Z = 4

Data collection

CCD area-detector diffractometer	2860 independent reflections
Radiation source: fine-focus sealed tube	2415 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.053
ϕ and ω scans	θmax = 26.0°, θmin = 3.5°
Absorption correction: multi-scan (SADABS; Sheldrick, 2002)	h = −26→26
Tmin = 0.340, Tmax = 0.500	k = −10→10
26317 measured reflections	l = −9→9

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)] = 0.026	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.056	H-atom parameters not refined
S = 1.08	w = 1/[σ^2(Fo^2) + (0.0157P)^2 + 1.7696P] where P = (Fo^2 + 2Fc^2)/3
2860 reflections	(Δ/σ)max = 0.001
181 parameters	Δρmax = 0.38 e Å^−3
0 restraints	Δρmin = −0.46 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
Br2	0.495545 (13)	0.31359 (3)	0.26183 (4)	0.02697 (9)
Br1	0.941196 (15)	0.49131 (4)	−0.37098 (4)	0.03785 (10)
C1	0.89960 (13)	0.4979 (3)	−0.1706 (4)	0.0254 (6)
C2	0.92491 (13)	0.5843 (3)	−0.0303 (4)	0.0250 (6)
H2	0.9613	0.6415	−0.0337	0.030*
C3	0.89466 (13)	0.5832 (3)	0.1151 (4)	0.0244 (6)
H3	0.9111	0.6393	0.2116	0.029*
C4	0.84000 (13)	0.4991 (3)	0.1177 (3)	0.0197 (6)
C5	0.81399 (13)	0.4130 (3)	−0.0242 (3)	0.0197 (6)
C6	0.84548 (13)	0.4144 (3)	−0.1689 (4)	0.0245 (6)
H6	0.8296	0.3580	−0.2656	0.029*
C7	0.75441 (13)	0.3210 (3)	−0.0267 (3)	0.0205 (6)
H7A	0.7439	0.3147	0.0900	0.025*
H7B	0.7624	0.2191	−0.0641	0.025*
C8	0.69766 (12)	0.3856 (3)	−0.1449 (3)	0.0200 (6)
H8A	0.6633	0.3130	−0.1542	0.024*
H8B	0.7093	0.3999	−0.2594	0.024*
C9	0.67412 (13)	0.5368 (3)	−0.0809 (3)	0.0203 (6)
H9A	0.7087	0.6090	−0.0693	0.024*
H9B	0.6408	0.5758	−0.1666	0.024*
C10	0.64926 (13)	0.5234 (3)	0.0897 (3)	0.0190 (6)
C11	0.59357 (13)	0.4441 (3)	0.0996 (3)	0.0197 (6)
H11	0.5712	0.4026	0.0000	0.024*
C12	0.57120 (12)	0.4265 (3)	0.2551 (4)	0.0199 (6)
C13	0.60248 (13)	0.4884 (3)	0.4063 (3)	0.0215 (6)
H13	0.5869	0.4753	0.5107	0.026*
C14	0.65715 (13)	0.5698 (3)	0.3983 (3)	0.0207 (6)
H14	0.6785	0.6137	0.4979	0.025*
C15	0.68039 (13)	0.5865 (3)	0.2412 (3)	0.0187 (6)
C16	0.79036 (13)	0.6263 (3)	0.3318 (3)	0.0243 (6)
H16A	0.8226	0.7035	0.3310	0.029*
H16B	0.7827	0.6124	0.4502	0.029*
O1	0.81220 (9)	0.4898 (2)	0.2689 (2)	0.0223 (4)
O2	0.73395 (8)	0.6748 (2)	0.2300 (2)	0.0217 (4)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Br2	0.01901 (15)	0.03477 (17)	0.02772 (15)	−0.00301 (13)	0.00537 (11)	0.00636 (13)
Br1	0.02554 (17)	0.0642 (2)	0.02601 (16)	0.00385 (16)	0.01132 (12)	0.00345 (15)
C1	0.0215 (15)	0.0351 (17)	0.0206 (14)	0.0086 (13)	0.0061 (11)	0.0047 (13)
C2	0.0161 (14)	0.0286 (16)	0.0298 (16)	0.0005 (12)	0.0018 (12)	0.0040 (12)
C3	0.0231 (15)	0.0271 (16)	0.0218 (14)	0.0028 (12)	−0.0007 (12)	−0.0006 (12)
C4	0.0204 (14)	0.0198 (14)	0.0191 (13)	0.0045 (12)	0.0028 (11)	0.0040 (11)
C5	0.0179 (14)	0.0188 (14)	0.0219 (14)	0.0059 (11)	0.0015 (11)	0.0027 (11)
C6	0.0235 (16)	0.0291 (17)	0.0205 (14)	0.0025 (12)	0.0017 (12)	−0.0027 (12)
C7	0.0239 (14)	0.0192 (14)	0.0190 (13)	−0.0010 (12)	0.0052 (11)	0.0002 (11)
C8	0.0201 (14)	0.0245 (14)	0.0158 (13)	−0.0028 (12)	0.0033 (11)	−0.0049 (12)
C9	0.0213 (14)	0.0215 (15)	0.0184 (13)	−0.0002 (11)	0.0039 (11)	0.0012 (11)
C10	0.0216 (14)	0.0158 (14)	0.0202 (13)	0.0037 (11)	0.0046 (11)	0.0032 (11)
C11	0.0202 (14)	0.0200 (14)	0.0187 (13)	0.0019 (11)	0.0016 (11)	0.0023 (11)
C12	0.0147 (14)	0.0182 (14)	0.0275 (15)	0.0039 (11)	0.0047 (11)	0.0035 (11)
C13	0.0253 (16)	0.0231 (15)	0.0174 (13)	0.0047 (12)	0.0076 (11)	0.0014 (12)
C14	0.0234 (15)	0.0191 (14)	0.0192 (14)	0.0028 (12)	0.0015 (11)	−0.0038 (11)
C15	0.0198 (14)	0.0150 (14)	0.0221 (14)	0.0010 (11)	0.0061 (11)	0.0010 (11)
C16	0.0230 (15)	0.0290 (15)	0.0208 (14)	−0.0023 (13)	0.0026 (11)	−0.0091 (13)
O1	0.0252 (11)	0.0251 (10)	0.0173 (9)	0.0018 (9)	0.0058 (8)	−0.0007 (8)
O2	0.0209 (10)	0.0201 (10)	0.0245 (10)	−0.0030 (8)	0.0051 (8)	−0.0024 (8)

Geometric parameters (Å, º)

Br2—C12	1.904 (3)	C8—H8B	0.9700
Br1—C1	1.904 (3)	C9—C10	1.506 (4)
C1—C6	1.372 (4)	C9—H9A	0.9700
C1—C2	1.383 (4)	C9—H9B	0.9700
C2—C3	1.382 (4)	C10—C11	1.390 (4)
C2—H2	0.9300	C10—C15	1.392 (4)
C3—C4	1.385 (4)	C11—C12	1.375 (4)
C3—H3	0.9300	C11—H11	0.9300
C4—C5	1.395 (4)	C12—C13	1.386 (4)
C4—O1	1.397 (3)	C13—C14	1.379 (4)
C5—C6	1.393 (4)	C13—H13	0.9300
C5—C7	1.507 (4)	C14—C15	1.394 (4)
C6—H6	0.9300	C14—H14	0.9300
C7—C8	1.528 (4)	C15—O2	1.396 (3)
C7—H7A	0.9700	C16—O1	1.407 (3)
C7—H7B	0.9700	C16—O2	1.413 (3)
C8—C9	1.536 (4)	C16—H16A	0.9700
C8—H8A	0.9700	C16—H16B	0.9700
C6—C1—C2	121.7 (3)	C10—C9—H9A	109.0
C6—C1—Br1	118.7 (2)	C8—C9—H9A	109.0
C2—C1—Br1	119.6 (2)	C10—C9—H9B	109.0
C3—C2—C1	118.2 (3)	C8—C9—H9B	109.0
C3—C2—H2	120.9	H9A—C9—H9B	107.8
C1—C2—H2	120.9	C11—C10—C15	117.7 (2)
C2—C3—C4	120.3 (3)	C11—C10—C9	119.8 (2)
C2—C3—H3	119.8	C15—C10—C9	122.5 (2)
C4—C3—H3	119.8	C12—C11—C10	120.7 (3)
C3—C4—C5	121.6 (3)	C12—C11—H11	119.7
C3—C4—O1	120.1 (2)	C10—C11—H11	119.7
C5—C4—O1	118.2 (2)	C11—C12—C13	121.6 (3)
C6—C5—C4	117.2 (3)	C11—C12—Br2	118.9 (2)
C6—C5—C7	119.6 (2)	C13—C12—Br2	119.5 (2)
C4—C5—C7	123.2 (2)	C14—C13—C12	118.5 (2)
C1—C6—C5	120.9 (3)	C14—C13—H13	120.7
C1—C6—H6	119.5	C12—C13—H13	120.7
C5—C6—H6	119.5	C13—C14—C15	120.0 (2)
C5—C7—C8	113.6 (2)	C13—C14—H14	120.0
C5—C7—H7A	108.8	C15—C14—H14	120.0
C8—C7—H7A	108.8	C10—C15—C14	121.4 (2)
C5—C7—H7B	108.8	C10—C15—O2	117.9 (2)
C8—C7—H7B	108.8	C14—C15—O2	120.5 (2)
H7A—C7—H7B	107.7	O1—C16—O2	111.1 (2)
C7—C8—C9	113.3 (2)	O1—C16—H16A	109.4
C7—C8—H8A	108.9	O2—C16—H16A	109.4
C9—C8—H8A	108.9	O1—C16—H16B	109.4
C7—C8—H8B	108.9	O2—C16—H16B	109.4
C9—C8—H8B	108.9	H16A—C16—H16B	108.0
H8A—C8—H8B	107.7	C4—O1—C16	116.4 (2)
C10—C9—C8	113.0 (2)	C15—O2—C16	115.8 (2)
C16—O1—C4—C3	62.4 (3)	C6—C5—C7—C8	−70.8 (3)
C16—O1—C4—C5	−122.3 (3)	C4—C5—C7—C8	109.1 (3)
C4—O1—C16—O2	74.2 (3)	C5—C7—C8—C9	−67.6 (3)
C16—O2—C15—C10	−122.0 (2)	C7—C8—C9—C10	−63.8 (3)
C16—O2—C15—C14	61.5 (3)	C8—C9—C10—C11	−68.3 (3)
C15—O2—C16—O1	69.0 (3)	C8—C9—C10—C15	111.0 (3)
Br1—C1—C6—C5	178.7 (2)	C9—C10—C15—O2	5.0 (4)
Br1—C1—C2—C3	−178.1 (2)	C11—C10—C15—C14	0.7 (4)
C6—C1—C2—C3	0.9 (4)	C9—C10—C15—C14	−178.6 (2)
C2—C1—C6—C5	−0.4 (4)	C11—C10—C15—O2	−175.8 (2)
C1—C2—C3—C4	−0.9 (4)	C9—C10—C11—C12	177.9 (2)
C2—C3—C4—O1	175.4 (2)	C15—C10—C11—C12	−1.4 (4)
C2—C3—C4—C5	0.3 (4)	C10—C11—C12—Br2	−178.8 (2)
O1—C4—C5—C7	5.2 (4)	C10—C11—C12—C13	1.0 (4)
C3—C4—C5—C6	0.3 (4)	Br2—C12—C13—C14	−180.0 (2)
O1—C4—C5—C6	−174.9 (2)	C11—C12—C13—C14	0.3 (4)
C3—C4—C5—C7	−179.6 (3)	C12—C13—C14—C15	−1.0 (4)
C4—C5—C6—C1	−0.3 (4)	C13—C14—C15—O2	176.9 (2)
C7—C5—C6—C1	179.6 (3)	C13—C14—C15—C10	0.5 (4)

(III) 7,19-dibromo-11,15-dioxatricyclo[14.4.0.0^5,10]icosaa-5,7,9,16,18,20-hexaene

Crystal data

C18H18Br2O2	F(000) = 1696
Mr = 426.14	Dx = 1.697 Mg m^−3
Orthorhombic, Pbca	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ac 2ab	Cell parameters from 5030 reflections
a = 13.7971 (5) Å	θ = 3.0–18.2°
b = 8.5744 (3) Å	µ = 4.87 mm^−1
c = 28.1906 (10) Å	T = 150 K
V = 3335.0 (2) Å^3	Prism, colorless
Z = 8	0.25 × 0.17 × 0.11 mm

Data collection

CCD area-detector diffractometer	3270 independent reflections
Radiation source: fine-focus sealed tube	2067 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.156
ϕ and ω scans	θmax = 26.0°, θmin = 3.3°
Absorption correction: multi-scan (SADABS; Sheldrick, 2002)	h = −17→17
Tmin = 0.380, Tmax = 0.607	k = −10→10
81249 measured reflections	l = −34→34

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)] = 0.040	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.100	H-atom parameters not refined
S = 1.03	w = 1/[σ^2(Fo^2) + (0.0405P)^2 + 3.5204P] where P = (Fo^2 + 2Fc^2)/3
3270 reflections	(Δ/σ)max = 0.001
199 parameters	Δρmax = 0.32 e Å^−3
0 restraints	Δρmin = −0.45 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
Br1	0.84124 (4)	0.56142 (6)	0.888508 (19)	0.05551 (19)
Br2	0.91741 (4)	0.17270 (6)	0.48567 (2)	0.04864 (18)
C1	0.8473 (3)	0.6518 (5)	0.82705 (16)	0.0375 (11)
C2	0.7773 (3)	0.7581 (6)	0.81338 (18)	0.0432 (12)
H2	0.7264	0.7832	0.8336	0.052*
C3	0.7844 (3)	0.8264 (5)	0.76936 (18)	0.0396 (12)
H3	0.7374	0.8975	0.7598	0.047*
C4	0.8600 (3)	0.7909 (5)	0.73915 (16)	0.0307 (10)
C5	0.9304 (3)	0.6797 (5)	0.75269 (16)	0.0306 (10)
C6	0.9221 (3)	0.6120 (5)	0.79684 (16)	0.0324 (11)
H6	0.9676	0.5384	0.8064	0.039*
C7	0.8039 (3)	0.9588 (5)	0.67602 (17)	0.0391 (12)
H16A	0.7951	1.0497	0.6960	0.047*
H16B	0.7425	0.9043	0.6737	0.047*
C8	0.8374 (3)	1.0081 (5)	0.62746 (17)	0.0392 (12)
H8A	0.9045	1.0411	0.6297	0.047*
H8B	0.7995	1.0978	0.6177	0.047*
C9	0.8298 (3)	0.8850 (5)	0.58938 (17)	0.0354 (11)
H17A	0.7641	0.8449	0.5879	0.043*
H17B	0.8460	0.9294	0.5587	0.043*
C10	0.8972 (3)	0.6333 (5)	0.57272 (16)	0.0316 (11)
C11	0.8421 (3)	0.6148 (5)	0.53215 (16)	0.0321 (10)
H15	0.8014	0.6949	0.5222	0.038*
C12	0.8470 (3)	0.4780 (5)	0.50624 (17)	0.0376 (11)
H14	0.8092	0.4654	0.4792	0.045*
C13	0.9083 (3)	0.3608 (5)	0.52079 (17)	0.0365 (11)
C14	0.9649 (3)	0.3791 (5)	0.56123 (17)	0.0362 (11)
H12	1.0055	0.2985	0.5708	0.043*
C15	0.9616 (3)	0.5150 (5)	0.58746 (16)	0.0327 (11)
C16	1.0229 (3)	0.5411 (6)	0.63035 (16)	0.0365 (11)
H20A	1.0553	0.6410	0.6275	0.044*
H20B	1.0723	0.4608	0.6318	0.044*
C17	0.9642 (3)	0.5387 (5)	0.67668 (15)	0.0313 (10)
H19A	0.8995	0.5776	0.6701	0.038*
H19B	0.9578	0.4313	0.6871	0.038*
C18	1.0072 (3)	0.6341 (5)	0.71733 (16)	0.0343 (11)
H18A	1.0569	0.5734	0.7332	0.041*
H18B	1.0374	0.7274	0.7047	0.041*
O1	0.8762 (2)	0.8577 (3)	0.69613 (11)	0.0342 (7)
O2	0.8960 (2)	0.7615 (3)	0.60083 (10)	0.0335 (7)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Br1	0.0667 (4)	0.0603 (3)	0.0395 (3)	−0.0217 (3)	0.0006 (3)	−0.0012 (3)
Br2	0.0478 (3)	0.0402 (3)	0.0579 (4)	−0.0080 (2)	0.0178 (3)	−0.0057 (3)
C1	0.043 (3)	0.035 (3)	0.035 (3)	−0.012 (2)	−0.003 (2)	−0.007 (2)
C2	0.035 (3)	0.047 (3)	0.048 (3)	−0.009 (2)	0.003 (3)	−0.018 (3)
C3	0.032 (3)	0.034 (3)	0.053 (3)	0.000 (2)	−0.002 (2)	−0.013 (3)
C4	0.026 (2)	0.026 (2)	0.041 (3)	0.0016 (18)	−0.001 (2)	−0.001 (2)
C5	0.024 (2)	0.030 (2)	0.038 (3)	−0.003 (2)	−0.004 (2)	−0.002 (2)
C6	0.028 (2)	0.028 (2)	0.041 (3)	−0.004 (2)	−0.006 (2)	−0.005 (2)
C7	0.030 (3)	0.033 (3)	0.054 (3)	0.014 (2)	−0.009 (2)	−0.003 (2)
C8	0.035 (3)	0.022 (2)	0.061 (3)	0.003 (2)	−0.015 (3)	0.005 (2)
C9	0.032 (3)	0.030 (2)	0.044 (3)	0.003 (2)	−0.006 (2)	0.011 (2)
C10	0.027 (3)	0.034 (2)	0.034 (3)	−0.0014 (19)	0.007 (2)	0.007 (2)
C11	0.025 (2)	0.034 (2)	0.037 (3)	0.003 (2)	0.006 (2)	0.011 (2)
C12	0.034 (3)	0.044 (3)	0.035 (3)	−0.006 (2)	0.007 (2)	0.006 (2)
C13	0.032 (3)	0.038 (3)	0.039 (3)	−0.004 (2)	0.014 (2)	−0.003 (2)
C14	0.032 (3)	0.036 (3)	0.041 (3)	0.004 (2)	0.012 (2)	0.009 (2)
C15	0.027 (2)	0.037 (3)	0.034 (3)	0.003 (2)	0.005 (2)	0.010 (2)
C16	0.025 (3)	0.041 (3)	0.043 (3)	0.011 (2)	0.004 (2)	0.006 (2)
C17	0.027 (2)	0.025 (2)	0.042 (3)	0.0051 (19)	−0.001 (2)	0.002 (2)
C18	0.022 (2)	0.038 (3)	0.044 (3)	0.008 (2)	−0.004 (2)	0.007 (2)
O1	0.0264 (16)	0.0312 (17)	0.045 (2)	0.0102 (13)	−0.0033 (15)	0.0037 (15)
O2	0.0288 (17)	0.0307 (16)	0.0410 (19)	0.0072 (13)	−0.0049 (14)	0.0031 (15)

Geometric parameters (Å, º)

Br1—C1	1.900 (5)	C9—H17A	0.9700
Br2—C13	1.897 (4)	C9—H17B	0.9700
C1—C6	1.382 (6)	C10—O2	1.355 (5)
C1—C2	1.382 (7)	C10—C11	1.382 (6)
C2—C3	1.375 (7)	C10—C15	1.412 (6)
C2—H2	0.9300	C11—C12	1.383 (6)
C3—C4	1.381 (6)	C11—H15	0.9300
C3—H3	0.9300	C12—C13	1.375 (6)
C4—O1	1.359 (5)	C12—H14	0.9300
C4—C5	1.413 (6)	C13—C14	1.391 (7)
C5—C6	1.378 (6)	C14—C15	1.380 (6)
C5—C18	1.507 (6)	C14—H12	0.9300
C6—H6	0.9300	C15—C16	1.492 (6)
C7—O1	1.438 (5)	C16—C17	1.537 (6)
C7—C8	1.505 (6)	C16—H20A	0.9700
C7—H16A	0.9700	C16—H20B	0.9700
C7—H16B	0.9700	C17—C18	1.528 (6)
C8—C9	1.509 (6)	C17—H19A	0.9700
C8—H8A	0.9700	C17—H19B	0.9700
C8—H8B	0.9700	C18—H18A	0.9700
C9—O2	1.435 (5)	C18—H18B	0.9700
C6—C1—C2	120.9 (5)	O2—C10—C15	114.7 (4)
C6—C1—Br1	119.6 (4)	C11—C10—C15	120.5 (4)
C2—C1—Br1	119.5 (4)	C10—C11—C12	120.5 (4)
C3—C2—C1	118.9 (5)	C10—C11—H15	119.8
C3—C2—H2	120.6	C12—C11—H15	119.8
C1—C2—H2	120.6	C13—C12—C11	119.5 (5)
C2—C3—C4	121.1 (5)	C13—C12—H14	120.3
C2—C3—H3	119.5	C11—C12—H14	120.3
C4—C3—H3	119.5	C12—C13—C14	120.5 (4)
O1—C4—C3	125.5 (4)	C12—C13—Br2	120.4 (4)
O1—C4—C5	114.4 (4)	C14—C13—Br2	119.1 (3)
C3—C4—C5	120.1 (4)	C15—C14—C13	121.1 (4)
C6—C5—C4	118.2 (4)	C15—C14—H12	119.5
C6—C5—C18	123.1 (4)	C13—C14—H12	119.5
C4—C5—C18	118.6 (4)	C14—C15—C10	118.0 (4)
C5—C6—C1	120.9 (4)	C14—C15—C16	122.8 (4)
C5—C6—H6	119.5	C10—C15—C16	119.2 (4)
C1—C6—H6	119.5	C15—C16—C17	112.8 (4)
O1—C7—C8	108.4 (4)	C15—C16—H20A	109.0
O1—C7—H16A	110.0	C17—C16—H20A	109.0
C8—C7—H16A	110.0	C15—C16—H20B	109.0
O1—C7—H16B	110.0	C17—C16—H20B	109.0
C8—C7—H16B	110.0	H20A—C16—H20B	107.8
H16A—C7—H16B	108.4	C18—C17—C16	115.2 (4)
C7—C8—C9	115.4 (4)	C18—C17—H19A	108.5
C7—C8—H8A	108.4	C16—C17—H19A	108.5
C9—C8—H8A	108.4	C18—C17—H19B	108.5
C7—C8—H8B	108.4	C16—C17—H19B	108.5
C9—C8—H8B	108.4	H19A—C17—H19B	107.5
H8A—C8—H8B	107.5	C5—C18—C17	111.2 (3)
O2—C9—C8	108.2 (3)	C5—C18—H18A	109.4
O2—C9—H17A	110.1	C17—C18—H18A	109.4
C8—C9—H17A	110.1	C5—C18—H18B	109.4
O2—C9—H17B	110.1	C17—C18—H18B	109.4
C8—C9—H17B	110.1	H18A—C18—H18B	108.0
H17A—C9—H17B	108.4	C4—O1—C7	119.5 (3)
O2—C10—C11	124.8 (4)	C10—O2—C9	118.3 (3)
C7—O1—C4—C3	−9.0 (6)	C4—C5—C6—C1	−0.1 (6)
C7—O1—C4—C5	172.8 (4)	O1—C7—C8—C9	74.6 (4)
C4—O1—C7—C8	−176.6 (3)	C7—C8—C9—O2	−65.9 (4)
C9—O2—C10—C11	3.1 (6)	O2—C10—C11—C12	−178.8 (4)
C10—O2—C9—C8	176.2 (3)	C15—C10—C11—C12	2.1 (7)
C9—O2—C10—C15	−177.7 (4)	O2—C10—C15—C14	178.3 (4)
Br1—C1—C2—C3	177.9 (3)	O2—C10—C15—C16	−1.6 (6)
C2—C1—C6—C5	1.5 (7)	C11—C10—C15—C14	−2.4 (6)
Br1—C1—C6—C5	−177.7 (3)	C11—C10—C15—C16	177.6 (4)
C6—C1—C2—C3	−1.3 (7)	C10—C11—C12—C13	−0.9 (7)
C1—C2—C3—C4	−0.3 (7)	C11—C12—C13—Br2	−179.4 (3)
C2—C3—C4—C5	1.7 (7)	C11—C12—C13—C14	0.1 (7)
C2—C3—C4—O1	−176.4 (4)	Br2—C13—C14—C15	179.1 (3)
O1—C4—C5—C6	176.9 (4)	C12—C13—C14—C15	−0.5 (7)
C3—C4—C5—C6	−1.5 (6)	C13—C14—C15—C10	1.6 (6)
C3—C4—C5—C18	175.1 (4)	C13—C14—C15—C16	−178.4 (4)
O1—C4—C5—C18	−6.6 (6)	C10—C15—C16—C17	71.1 (5)
C6—C5—C18—C17	106.5 (5)	C14—C15—C16—C17	−108.9 (5)
C18—C5—C6—C1	−176.5 (4)	C15—C16—C17—C18	−153.0 (4)
C4—C5—C18—C17	−69.8 (5)	C16—C17—C18—C5	156.8 (4)