(2RS,4SR)-7-Bromo-2-exo-(2-chloro­phenyl)-2,3,4,5-tetra­hydro-1,4-ep­oxy­naphtho[1,2-b]azepine: sheets built by the [pi]-stacking of hydrogen-bonded chains

The mol­ecules of the title compound, C₂₀H₁₅BrClNO, are linked into chains by a C-H...[pi](arene) hydrogen bond, in which the acceptor is the brominated ring of the naphthalene unit, and these chains are linked by an aromatic [pi]-[pi] stacking inter­action, again involving the naphthalene unit, into a sheet structure.

S1. Comment

We report here the molecular and supramolecular structure of the title compound, (I) (Fig. 1), which we compare with the positional isomer (II) (see scheme), the structure of which was reported recently (Palma et al., 2009). The synthetic route involves the oxidation of the corresponding 2-allyl-N-arylmethyl-1-naphthylamine with an excess of aqueous hydrogen peroxide in the presence of catalytic quantities of sodium tungstate, followed by a thermally induced intramolecular 1,3-dipolar cycloaddition of the intermediate nitrone (cf. Acosta et al., 2008).

The molecule of (I) contains two stereogenic centres, at atoms C2 and C4 (Fig. 1), and the reference molecule was selected to have the R configuration at C2; on this basis, the configuration at C4 is S. Since (I) crystallizes in the centrosymmetric space group P2₁/c, the unit cell accommodates equal numbers of the two enantiomers, so that the compound crystallizes as a true racemate with conformation (2RS,4SR). The isomeric compound (II) also crystallizes as a racemate, with the configuration (2RS,4SR), but in a different centrosymmetric space group, viz. Pbca.

The conformations of the fused heterocyclic ring systems in (I) and (II) are very similar, as shown by the values (Table 2) of the ring-puckering parameters (Cremer & Pople, 1975). The five-membered rings are twisted about a line between atom C3 and the mid-point of the N1—O14 bond. The six-membered rings have conformations intermediate between envelope and half-chair forms. For a six-membered ring with equal bond lengths, the idealized values of the ring-puckering parameters are θ = 54.7° and ϕ = (60k)° for the envelope conformation, and θ = 50.8° and ϕ = (60k + 30)° for the half-chair form, where k represents an integer in both cases. The specification of the molecular conformation can be completed by the torsion angle N1—C2—C21—C22 defining the orientation of the pendant aryl ring relative to the fused ring system; the values of this angle in (I) and (II) are fairly similar, viz. -173.87 (19)° in (I) and 172.4 (3)° in (II).

Thus, despite the different crystallization behaviour, as shown by the different space groups, the molecular conformations of (I) and (II) are very similar. However, the supramolecular assembly in these two compounds is significantly different.

The crystal structure of (I) contains no C—H···O or C—H···N hydrogen bonds, and the supramolecular assembly is determined by a combination of a C—H···π(arene) hydrogen bond (Table 1) and an aromatic π–π stacking interaction. The C—H···π(arene) hydrogen bond utilizes the brominated ring of the naphthalene unit as the acceptor, and it links molecules related by the 2₁ screw axis along (1/2, y, 3/4) into a chain running parallel to the [010] direction (Fig. 2).

Within the naphthalene unit, the two rings are not quite parallel and the angle between the normals of the two six-membered rings is 2.76 (11)°. In the aromatic π–π stacking interaction (Fig. 3), the distance between the centroid of the brominated ring C5a/C6/C7/C7a/C11a/C11b of the molecule at (x, y, z) and that of the unsubstituted ring C7a/C8/C9/C10/C11/C11a in the molecule at (-x, -y + 1, z + 1) is 3.816 (2) Å. These rings make a dihedral angle of 2.76 (11)° and the distance between the ring planes is ca 3.46 Å. Thus, the molecules at (x, y, z) and (-x + 1, y + 1/2, -z + 3/2), which form parts of the hydrogen-bonded chain along (1/2, y, 3/4), form π–π stacking interactions with the molecules at (-x, -y + 1, -z + 1) and (x + 1, -y + 1/2, z + 1/2), respectively, which form parts of the hydrogen-bonded chains along (-1/2, y, 1/4) and (3/2, y, 5/4), respectively. Hence the action of the π–π stacking interaction is to link the hydrogen-bonded chains which run parallel to [010] into a sheet lying parallel to (102) (Fig. 4). Both faces of the naphthalene unit are involved in the sheet formation, with one face acting as the hydrogen-bond acceptor, while the other participates in the π–π stacking interaction (Fig. 4).

By contrast, there are no C—H···π hydrogen bonds in the structure of (II). Instead, the assembly in (II) is determined by a combination of a C—H···O hydrogen bond and an aromatic π–π stacking interaction involving the pendant 4-chlorophenyl rings of inversion-related pairs of molecules (Palma et al., 2009). The C—H···O hydrogen bond links molecules related by a b-glide plane in space group Pbca into a chain running parallel to [010], and these chains are linked by the π–π stacking interaction into a sheet lying parallel to (001).

It is of interest to note here that, although the structures of (I) and (II) contain π–π stacking interactions, these involve only the naphthalene unit in (I) and only the pendant phenyl ring in (II).

Related literature

For related literature, see: Acosta et al. (2008); Cremer & Pople (1975); Palma et al. (2009).

S2. Experimental

Sodium tungstate dihydrate (5–10 mol%), followed by 30% aqueous hydrogen peroxide solution (30 mmol), were added to a stirred and cooled (ice-bath) solution of 2-allyl-4-bromo-N-(2-chlorobenzyl)-1-naphthylamine (10 mmol) in acetone–water (30 ml, 10:1 v/v). The resulting mixture was stirred at 273 K for 2 h and then at ambient temperature for an additional 72 h. The reaction mixture was filtered and then extracted with ethyl acetate, and the organic fraction was dried over anhydrous sodium sulfate. The solvent was removed under reduced pressure, and then toluene (30 ml) was added to the solid residue. The resulting solution was heated at 363–373 K for 12 h. The solution was then cooled to ambient temperature and the solvent was removed under reduced pressure, before the crude product was purified by silica-gel column chromatography using heptane–ethyl acetate (from 30:1 to 10:1 v/v) as eluent, to obtain the product, (I), as pale-yellow crystals suitable for single-crystal X-ray diffraction (yield 48%, m.p. 464–465 K). MS (70 eV) m/z (%): 399 (M⁺, ³⁵Cl, ⁷⁹Br, 1), 365 (100), 348 (6), 322 (2), 335 (4), 257 (3), 231 (1).

S3. Refinement

All H atoms were located in difference maps and then treated as riding atoms in geometrically idealized positions, with C—H = 0.95 (aromatic), 0.99 (CH₂) or 1.00 Å (aliphatic CH), and with U_iso(H) = 1.2U_eq(C).

Computing details

Data collection: COLLECT (Nonius, 1999); cell refinement: DIRAX/LSQ (Duisenberg et al., 2000); data reduction: EVALCCD (Duisenberg et al., 2003); program(s) used to solve structure: SIR2004 (Burla et al., 2005); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: PLATON (Spek, 2009); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008) and PLATON (Spek, 2009).

Figures

	Fig. 1. The molecular structure of (I), showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 30% probability level.
	Fig. 2. Part of the crystal structure of (I), showing the formation of a hydrogen-bonded chain parallel to [010]. For the sake of clarity, H atoms not involved in the motif shown have been omitted. Atoms marked with an asterisk (*), a hash (#), a dollar sign ($) or an ampersand (&) are at the symmetry positions (-x + 1, y - 1/2, -z + 3/2), (x, y - 1, z), (-x + 1, y + 1/2, -z + 3/2) and (x, y + 1, z), respectively.
	Fig. 3. Part of the crystal structure of (I), showing the π–π stacking interaction which links the hydrogen-bonded chains. For the sake of clarity, H atoms have been omitted. The atom marked with an asterisk (*) is at the symmetry position (-x, -y + 1, -z + 1).
	Fig. 4. A stereoview of part of the crystal structure of (I), showing the formation of a sheet parallel to (102) formed by the π-stacking of hydrogen-bonded chains. For the sake of clarity, H atoms not involved in the motifs shown have been omitted.

7-bromo-2-exo-(2-chlorophenyl)-2,3,4,5-tetrahydro- 1,4-epoxynaphtho[1,2-b]azepine

Crystal data

C20H15BrClNO	F(000) = 808
Mr = 400.68	Dx = 1.663 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 23672 reflections
a = 11.5083 (8) Å	θ = 3.1–27.5°
b = 8.1027 (6) Å	µ = 2.74 mm^−1
c = 18.3210 (16) Å	T = 120 K
β = 110.505 (5)°	Plate, pale yellow
V = 1600.2 (2) Å^3	0.38 × 0.30 × 0.10 mm
Z = 4

Data collection

Bruker Nonius KappaCCD area-detector diffractometer	3672 independent reflections
Radiation source: Bruker Nonius FR591 rotating anode	2969 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.041
Detector resolution: 9.091 pixels mm^-1	θmax = 27.5°, θmin = 3.1°
ϕ and ω scans	h = −13→14
Absorption correction: multi-scan (SADABS; Sheldrick, 2003)	k = −9→10
Tmin = 0.422, Tmax = 0.771	l = −23→23
22802 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)] = 0.034	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.069	H-atom parameters constrained
S = 1.12	w = 1/[σ^2(Fo^2) + (0.0219P)^2 + 1.5269P] where P = (Fo^2 + 2Fc^2)/3
3672 reflections	(Δ/σ)max = 0.001
217 parameters	Δρmax = 0.39 e Å^−3
0 restraints	Δρmin = −0.37 e Å^−3

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

	x	y	z	Uiso*/Ueq
N1	0.30373 (17)	0.4120 (2)	0.56731 (10)	0.0160 (4)
C2	0.4182 (2)	0.4418 (3)	0.63424 (12)	0.0147 (4)
H2	0.3969	0.4615	0.6819	0.018*
C3	0.4712 (2)	0.6025 (3)	0.61228 (13)	0.0184 (5)
H3A	0.4629	0.6964	0.6447	0.022*
H3B	0.5597	0.5891	0.6185	0.022*
C4	0.3915 (2)	0.6276 (3)	0.52732 (14)	0.0190 (5)
H4	0.4439	0.6614	0.4964	0.023*
C5	0.2851 (2)	0.7478 (3)	0.51442 (14)	0.0199 (5)
H5A	0.3170	0.8535	0.5410	0.024*
H5B	0.2447	0.7701	0.4580	0.024*
C5a	0.1928 (2)	0.6755 (3)	0.54616 (13)	0.0169 (5)
C6	0.0936 (2)	0.7702 (3)	0.55103 (13)	0.0192 (5)
H6	0.0824	0.8799	0.5315	0.023*
C7	0.0135 (2)	0.7071 (3)	0.58320 (13)	0.0190 (5)
Br7	−0.11653 (2)	0.84352 (3)	0.588544 (15)	0.02630 (8)
C7a	0.0256 (2)	0.5441 (3)	0.61313 (13)	0.0182 (5)
C8	−0.0522 (2)	0.4748 (3)	0.64992 (14)	0.0243 (5)
H8	−0.1194	0.5373	0.6541	0.029*
C9	−0.0315 (2)	0.3191 (3)	0.67948 (15)	0.0270 (6)
H9	−0.0830	0.2754	0.7055	0.032*
C10	0.0643 (2)	0.2226 (3)	0.67217 (14)	0.0250 (6)
H10	0.0771	0.1139	0.6929	0.030*
C11	0.1395 (2)	0.2837 (3)	0.63544 (13)	0.0200 (5)
H11	0.2030	0.2162	0.6294	0.024*
C11a	0.1238 (2)	0.4465 (3)	0.60636 (13)	0.0168 (5)
C11b	0.2052 (2)	0.5156 (3)	0.57208 (13)	0.0157 (5)
O14	0.33742 (15)	0.46699 (19)	0.50281 (9)	0.0186 (3)
C21	0.5053 (2)	0.2972 (3)	0.64787 (13)	0.0147 (5)
C22	0.6136 (2)	0.2937 (3)	0.71277 (13)	0.0177 (5)
Cl22	0.64630 (6)	0.45655 (8)	0.77856 (3)	0.02621 (14)
C23	0.6963 (2)	0.1646 (3)	0.72798 (14)	0.0222 (5)
H23	0.7691	0.1657	0.7732	0.027*
C24	0.6720 (2)	0.0333 (3)	0.67669 (15)	0.0236 (5)
H24	0.7286	−0.0564	0.6863	0.028*
C25	0.5660 (2)	0.0329 (3)	0.61186 (14)	0.0217 (5)
H25	0.5494	−0.0568	0.5763	0.026*
C26	0.4830 (2)	0.1632 (3)	0.59818 (13)	0.0181 (5)
H26	0.4092	0.1603	0.5536	0.022*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N1	0.0181 (10)	0.0182 (9)	0.0128 (9)	−0.0009 (8)	0.0068 (8)	0.0012 (8)
C2	0.0155 (11)	0.0152 (11)	0.0128 (11)	−0.0018 (9)	0.0041 (9)	−0.0010 (9)
C3	0.0185 (11)	0.0151 (11)	0.0217 (12)	−0.0013 (9)	0.0073 (10)	−0.0001 (9)
C4	0.0222 (12)	0.0160 (12)	0.0219 (12)	−0.0014 (9)	0.0117 (10)	0.0024 (9)
C5	0.0208 (12)	0.0186 (12)	0.0206 (12)	0.0008 (10)	0.0075 (10)	0.0070 (10)
C5a	0.0144 (11)	0.0202 (12)	0.0147 (11)	−0.0008 (9)	0.0032 (9)	0.0007 (9)
C6	0.0189 (11)	0.0177 (11)	0.0172 (12)	0.0015 (10)	0.0017 (10)	0.0013 (10)
C7	0.0140 (11)	0.0229 (12)	0.0170 (12)	0.0012 (9)	0.0017 (9)	−0.0048 (10)
Br7	0.01782 (12)	0.02671 (13)	0.03345 (15)	0.00318 (11)	0.00781 (10)	−0.00495 (12)
C7a	0.0127 (11)	0.0232 (12)	0.0154 (11)	−0.0032 (9)	0.0007 (9)	−0.0033 (10)
C8	0.0161 (12)	0.0333 (14)	0.0224 (13)	−0.0044 (11)	0.0053 (10)	−0.0015 (11)
C9	0.0192 (12)	0.0375 (16)	0.0244 (13)	−0.0089 (11)	0.0078 (10)	0.0056 (12)
C10	0.0226 (13)	0.0262 (13)	0.0231 (13)	−0.0054 (11)	0.0040 (11)	0.0056 (11)
C11	0.0162 (11)	0.0215 (12)	0.0190 (12)	−0.0034 (10)	0.0018 (10)	0.0010 (10)
C11a	0.0149 (11)	0.0194 (12)	0.0125 (11)	−0.0039 (9)	0.0002 (9)	0.0000 (9)
C11b	0.0148 (11)	0.0164 (11)	0.0142 (11)	−0.0005 (9)	0.0030 (9)	−0.0011 (9)
O14	0.0252 (9)	0.0184 (8)	0.0144 (8)	−0.0014 (7)	0.0100 (7)	0.0010 (7)
C21	0.0167 (11)	0.0150 (11)	0.0154 (11)	−0.0018 (8)	0.0094 (9)	0.0013 (9)
C22	0.0181 (11)	0.0201 (12)	0.0175 (11)	−0.0021 (9)	0.0095 (10)	0.0009 (9)
Cl22	0.0264 (3)	0.0278 (3)	0.0198 (3)	−0.0025 (3)	0.0023 (2)	−0.0046 (3)
C23	0.0170 (11)	0.0274 (13)	0.0229 (12)	0.0014 (10)	0.0080 (10)	0.0086 (11)
C24	0.0236 (12)	0.0218 (13)	0.0321 (14)	0.0069 (10)	0.0181 (11)	0.0100 (11)
C25	0.0295 (13)	0.0171 (12)	0.0252 (13)	0.0005 (10)	0.0178 (11)	0.0010 (10)
C26	0.0206 (11)	0.0170 (11)	0.0187 (11)	−0.0007 (10)	0.0095 (9)	0.0026 (10)

Geometric parameters (Å, º)

N1—O14	1.438 (2)	C7a—C11a	1.420 (3)
N1—C11b	1.438 (3)	C8—C9	1.360 (4)
N1—C2	1.472 (3)	C8—H8	0.9500
C2—C21	1.505 (3)	C9—C10	1.395 (4)
C2—C3	1.550 (3)	C9—H9	0.9500
C2—H2	1.0000	C10—C11	1.362 (3)
C3—C4	1.518 (3)	C10—H10	0.9500
C3—H3A	0.9900	C11—C11a	1.410 (3)
C3—H3B	0.9900	C11—H11	0.9500
C4—O14	1.444 (3)	C11a—C11b	1.414 (3)
C4—C5	1.517 (3)	C21—C26	1.382 (3)
C4—H4	1.0000	C21—C22	1.390 (3)
C5—C5a	1.498 (3)	C22—C23	1.375 (3)
C5—H5A	0.9900	C22—Cl22	1.737 (2)
C5—H5B	0.9900	C23—C24	1.382 (4)
C5a—C11b	1.370 (3)	C23—H23	0.9500
C5a—C6	1.404 (3)	C24—C25	1.373 (4)
C6—C7	1.356 (3)	C24—H24	0.9500
C6—H6	0.9500	C25—C26	1.386 (3)
C7—C7a	1.418 (3)	C25—H25	0.9500
C7—Br7	1.891 (2)	C26—H26	0.9500
C7a—C8	1.412 (3)
O14—N1—C11b	108.31 (16)	C7—C7a—C11a	117.2 (2)
O14—N1—C2	102.32 (15)	C9—C8—C7a	120.5 (2)
C11b—N1—C2	110.36 (17)	C9—C8—H8	119.8
N1—C2—C21	111.09 (18)	C7a—C8—H8	119.8
N1—C2—C3	103.94 (17)	C8—C9—C10	121.0 (2)
C21—C2—C3	113.42 (18)	C8—C9—H9	119.5
N1—C2—H2	109.4	C10—C9—H9	119.5
C21—C2—H2	109.4	C11—C10—C9	120.2 (2)
C3—C2—H2	109.4	C11—C10—H10	119.9
C4—C3—C2	103.11 (18)	C9—C10—H10	119.9
C4—C3—H3A	111.1	C10—C11—C11a	120.5 (2)
C2—C3—H3A	111.1	C10—C11—H11	119.8
C4—C3—H3B	111.1	C11a—C11—H11	119.8
C2—C3—H3B	111.1	C11—C11a—C11b	121.4 (2)
H3A—C3—H3B	109.1	C11—C11a—C7a	119.2 (2)
O14—C4—C5	107.11 (18)	C11b—C11a—C7a	119.4 (2)
O14—C4—C3	103.78 (17)	C5a—C11b—C11a	121.5 (2)
C5—C4—C3	114.26 (19)	C5a—C11b—N1	121.4 (2)
O14—C4—H4	110.5	C11a—C11b—N1	117.1 (2)
C5—C4—H4	110.5	N1—O14—C4	103.56 (15)
C3—C4—H4	110.5	C26—C21—C22	116.8 (2)
C5a—C5—C4	109.38 (19)	C26—C21—C2	122.9 (2)
C5a—C5—H5A	109.8	C22—C21—C2	120.2 (2)
C4—C5—H5A	109.8	C23—C22—C21	122.6 (2)
C5a—C5—H5B	109.8	C23—C22—Cl22	118.10 (18)
C4—C5—H5B	109.8	C21—C22—Cl22	119.30 (18)
H5A—C5—H5B	108.2	C22—C23—C24	119.2 (2)
C11b—C5a—C6	118.9 (2)	C22—C23—H23	120.4
C11b—C5a—C5	120.1 (2)	C24—C23—H23	120.4
C6—C5a—C5	120.9 (2)	C25—C24—C23	119.8 (2)
C7—C6—C5a	120.9 (2)	C25—C24—H24	120.1
C7—C6—H6	119.6	C23—C24—H24	120.1
C5a—C6—H6	119.6	C24—C25—C26	120.1 (2)
C6—C7—C7a	122.0 (2)	C24—C25—H25	119.9
C6—C7—Br7	118.22 (18)	C26—C25—H25	119.9
C7a—C7—Br7	119.76 (17)	C21—C26—C25	121.5 (2)
C8—C7a—C7	124.2 (2)	C21—C26—H26	119.3
C8—C7a—C11a	118.5 (2)	C25—C26—H26	119.3
O14—N1—C2—C21	−86.58 (19)	C6—C5a—C11b—C11a	−2.6 (3)
C11b—N1—C2—C21	158.33 (18)	C5—C5a—C11b—C11a	176.4 (2)
O14—N1—C2—C3	35.74 (19)	C6—C5a—C11b—N1	178.9 (2)
C11b—N1—C2—C3	−79.3 (2)	C5—C5a—C11b—N1	−2.0 (3)
N1—C2—C3—C4	−10.3 (2)	C11—C11a—C11b—C5a	−177.8 (2)
C21—C2—C3—C4	110.5 (2)	C7a—C11a—C11b—C5a	0.9 (3)
C2—C3—C4—O14	−18.7 (2)	C11—C11a—C11b—N1	0.8 (3)
C2—C3—C4—C5	97.6 (2)	C7a—C11a—C11b—N1	179.44 (19)
O14—C4—C5—C5a	46.9 (2)	O14—N1—C11b—C5a	−28.0 (3)
C3—C4—C5—C5a	−67.4 (2)	C2—N1—C11b—C5a	83.3 (2)
C4—C5—C5a—C11b	−7.5 (3)	O14—N1—C11b—C11a	153.52 (18)
C4—C5—C5a—C6	171.5 (2)	C2—N1—C11b—C11a	−95.2 (2)
C11b—C5a—C6—C7	2.2 (3)	C11b—N1—O14—C4	67.30 (19)
C5—C5a—C6—C7	−176.8 (2)	C2—N1—O14—C4	−49.28 (19)
C5a—C6—C7—C7a	−0.1 (3)	C5—C4—O14—N1	−79.03 (19)
C5a—C6—C7—Br7	179.32 (17)	C3—C4—O14—N1	42.2 (2)
C6—C7—C7a—C8	177.4 (2)	N1—C2—C21—C26	6.0 (3)
Br7—C7—C7a—C8	−2.0 (3)	C3—C2—C21—C26	−110.7 (2)
C6—C7—C7a—C11a	−1.6 (3)	N1—C2—C21—C22	−173.87 (19)
Br7—C7—C7a—C11a	179.00 (16)	C3—C2—C21—C22	69.5 (3)
C7—C7a—C8—C9	−177.7 (2)	C26—C21—C22—C23	0.1 (3)
C11a—C7a—C8—C9	1.3 (3)	C2—C21—C22—C23	180.0 (2)
C7a—C8—C9—C10	−1.9 (4)	C26—C21—C22—Cl22	−178.97 (16)
C8—C9—C10—C11	0.4 (4)	C2—C21—C22—Cl22	0.9 (3)
C9—C10—C11—C11a	1.8 (4)	C21—C22—C23—C24	0.6 (3)
C10—C11—C11a—C11b	176.3 (2)	Cl22—C22—C23—C24	179.72 (18)
C10—C11—C11a—C7a	−2.4 (3)	C22—C23—C24—C25	−0.4 (3)
C8—C7a—C11a—C11	0.8 (3)	C23—C24—C25—C26	−0.5 (3)
C7—C7a—C11a—C11	179.9 (2)	C22—C21—C26—C25	−1.1 (3)
C8—C7a—C11a—C11b	−177.9 (2)	C2—C21—C26—C25	179.1 (2)
C7—C7a—C11a—C11b	1.2 (3)	C24—C25—C26—C21	1.3 (3)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C23—H23···Cg^i	0.95	2.62	3.494 (3)	153

Symmetry code: (i) −x+1, y−1/2, −z+3/2.