(+)-(4R,5S)-4-Methyl-3-[2(R)-phenoxy­propion­yl]-5-phenyl­oxazolidin-2-one

Coumbarides, G.S.; Eames, J.; Motevalli, M.; Malatesti, N.; Yohannes, Y.

doi:10.1107/S1600536806031862

organic compounds

CRYSTALLOGRAPHIC
COMMUNICATIONS

ISSN: 2056-9890

Volume 62| Part 9| September 2006| Pages o4041-o4042

https://doi.org/10.1107/S1600536806031862

(+)-(4R,5S)-4-Methyl-3-[2(R)-phenoxypropionyl]-5-phenyloxazolidin-2-one

Gregory S. Coumbarides,^a Jason Eames,^b ^* Majid Motevalli,^a Nela Malatesti ^c and Yonas Yohannes ^a

^aDepartment of Chemistry, Queen Mary, University of London, Mile End Road, London E1 4NS, England, ^bDepartment of Chemistry, University of Hull, Cottingham Road, Kingston-upon-Hull HU6 7RX, England, and ^cDepartment of Chemistry, J. J. Strossmayer University of Osijek, Trg Sv. Trojstva 3, Osijek 31000, Croatia
^*Correspondence e-mail: j.eames@hull.ac.uk

(Received 27 June 2006; accepted 12 August 2006; online 23 August 2006)

In the title compound, C₁₉H₁₉NO₄, formed from enantiomerically pure (+)-(4R,5S)-4-methyl-5-phenyl-2-oxazolidinone and racemic 2-phenoxypropanoyl chloride, the two carbonyl groups are oriented anti to each other, and the two methyl groups are oriented anti to each other.

Comment

The title compound, (I), is the fifth in a series of structurally related compounds, introduced in our earlier report (Coumbarides et al., 2006 ). With R¹ = C₆H₅O, the reaction shown in that report yielded the anti–syn and syn–syn diastereomers in 44 and 45% yields, respectively. The title compound, (I), is the syn–syn diastereomer.

The conformation of (I) (Fig. 1) is closely comparable with that of the phenylpropionyl derivative (Coumbarides et al., 2006). The five-membered ring displays a twist conformation in which atoms C1 and C2 lie, respectively, 0.286 (5) Å above and 0.291 (5) Å below the plane defined by atoms O1, O2, N1 and C3. The two methyl groups (C4 and C19) lie anti to each other, on either side of the five-membered ring. The carbonyl groups (C3=O2 and C11=O3) are also oriented anti to each other [torsion angle O3—C11—N1—C3 = −171.2 (3)°], avoiding electrostatic repulsion between the two O atoms. The shortest intermolecular contacts (Fig. 2) are C—H⋯O interactions [H16⋯O2ⁱ = 2.66 Å; symmetry code: (i) $[{1\over 2}]$ − x, 2 − y, $[{1\over 2}]$ + z] and edge-to-face C—H⋯π interactions [H9⋯centroid(C13–C18) = 2.92 Å; symmetry code: (ii) 1 − x, $[{1\over 2}]$ + y, $[{3\over 2}]$ − z].

Figure 1
The molecular structure of (I)

, showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms have been omitted.

Figure 2
A view of (I)

along the b-axis direction. Displacement ellipsoids are drawn at the 50% probability level and H atoms have been omitted.

Experimental

The experimental procedure is comparable with that reported previously (Coumbarides et al., 2006). The actual quantities used for preparation of (I) were: n-butyllithium (12.42 ml, 2.5 M in hexanes, 31.0 mmol) and (R,S)-oxazolidinone (5.00 g, 28.2 mmol) in 60 ml tetrahydrofuran (THF), combined with a solution of (rac)-2-phenoxypropanoyl chloride (5.71 g, 31.0 mmol) in 10 ml THF. The crude residue was purified by flash column chromatography on silica gel, eluting with light petroleum (b.p. 313–333 K)/diethyl ether (1:1) to give a separable diastereoisomeric mixture in the approximate ratio anti–syn:syn–syn 50:50. The syn–syn diastereomer was isolated as colourless crystals {4.13 g, 45% yield, m.p. 403–404 K, R_F 0.42 [light petroleum b.p 313–333 K/diethyl ether, 1:1]}. Spectroscopic analysis: [α]²²_D = +69.8 (CHCl₃, 295 K, concentration 1.9 g per 100 ml); IR (CHCl₃, ν_max, cm⁻¹): 1770 (C=O), 1712 (C=O); ¹H NMR (250 MHz; CDCl₃): δ 7.44–7.21 (7H, m, 7 × CH; Ph_a and Ph_b), 6.99–6.84 (3H, t, J = 7.3 Hz, 3 × CH; Ph_a and/or Ph_b), 6.02 (1H, q, J = 6.6 Hz, PhCH), 5.75 (1H, d, J = 7.2 Hz, PhCHO), 5.69 (1H, m, CHN), 1.68 (3H, d, J = 6.6 Hz, CH₃CHCO), 0.90 (3H, d, J = 6.8 Hz, CH₃CHN); ¹³C NMR (67.9 MHz; CDCl₃): δ 172.2 (NC=O), 157.3 (i-CO; Ph), 152.9 (OC=O), 132.9 (i-C; Ph), 129.7, 129.1, 128.9, 125.7, 121.6, 115.0 (6 × CH; Ph_a and Ph_b), 80.8 (PhCHO), 71.7 (PhCH), 55.2 (CHN), 18.6 (CH₃), 14.5 (CH₃); found: MH⁺ 326.1393; C₁₉H₂₀NO₄ requires 326.1392.

Crystal data

C₁₉H₁₉NO₄
M_r = 325.35
Orthorhombic, P 2₁ 2₁ 2₁
a = 16.915 (12) Å
b = 10.634 (5) Å
c = 9.226 (6) Å
V = 1659.5 (18) Å³
Z = 4
D_x = 1.302 Mg m⁻³
Mo Kα radiation
μ = 0.09 mm⁻¹
T = 293 (2) K
Prism, colourless
0.40 × 0.30 × 0.30 mm

Data collection

Enraf–Nonius CAD-4 diffractometer
ω/2θ scans
Absorption correction: none
3072 measured reflections
1681 independent reflections
1115 reflections with I > 2σ(I)
R_int = 0.032
θ_max = 25.0°
2 standard reflections every 100 reflections intensity decay: 3%

Refinement

Refinement on F²
R[F² > 2σ(F²)] = 0.040
wR(F²) = 0.089
S = 1.01
1681 reflections
220 parameters
H-atom parameters constrained
w = 1/[σ²(F_o²) + (0.0441P)²] where P = (F_o² + 2F_c²)/3
(Δ/σ)_max < 0.001
Δρ_max = 0.14 e Å⁻³
Δρ_min = −0.14 e Å⁻³
Extinction correction: SHELXL97
Extinction coefficient: 0.017 (2)

H atoms were placed in geometrically idealized positions and constrained to ride on their parent atoms, with C—H = 0.93–0.98 Å and U_iso(H) = 1.2U_eq(C) or 1.5U_eq(methyl C). The methyl groups were allowed to rotate about their local threefold axes. In the absence of significant anomalous scattering effects, the few measured Friedel pairs have been merged. The absolute configuration is assigned on the basis of the known configuration of the starting material (Coumbarides et al., 2006).

Data collection: CAD-4-PC Software (Enraf–Nonius, 1994 ); cell refinement: CAD-4-PC Software; data reduction: XCAD4 (Harms & Wocadlo, 1995 ); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997 ); software used to prepare material for publication: WinGX (Farrugia, 1999 ).

Supporting information

Crystal structure: contains datablocks global, I. DOI: https://doi.org/10.1107/S1600536806031862/bi2034sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S1600536806031862/bi2034Isup2.hkl

Computing details top

Data collection: CAD-4-PC Software (Enraf–Nonius, 1994); cell refinement: CAD-4-PC Software; data reduction: XCAD4 (Harms & Wocadlo, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: WinGX (Farrugia, 1999).

(+)-(4R,5S)-4-Methyl-3-[2(R)-phenoxypropionyl]- 5-phenyloxazolidin-2-one top

Crystal data top

C₁₉H₁₉NO₄	F(000) = 688
M_r = 325.35	D_x = 1.302 Mg m⁻³
Orthorhombic, P2₁2₁2₁	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2ac 2ab	Cell parameters from 25 reflections
a = 16.915 (12) Å	θ = 10.1–12.0°
b = 10.634 (5) Å	µ = 0.09 mm⁻¹
c = 9.226 (6) Å	T = 293 K
V = 1659.5 (18) Å³	Prism, colourless
Z = 4	0.40 × 0.30 × 0.30 mm

Data collection top

Enraf–Nonius CAD-4 diffractometer	R_int = 0.032
Radiation source: fine-focus sealed tube	θ_max = 25.0°, θ_min = 2.3°
Graphite monochromator	h = −13→20
ω/2θ scans	k = −12→12
3072 measured reflections	l = −10→10
1681 independent reflections	2 standard reflections every 100 reflections
1115 reflections with I > 2σ(I)	intensity decay: 3%

Refinement top

Refinement on F²	Hydrogen site location: inferred from neighbouring sites
Least-squares matrix: full	H-atom parameters constrained
R[F² > 2σ(F²)] = 0.040	w = 1/[σ²(F_o²) + (0.0441P)²] where P = (F_o² + 2F_c²)/3
wR(F²) = 0.089	(Δ/σ)_max < 0.001
S = 1.02	Δρ_max = 0.14 e Å⁻³
1681 reflections	Δρ_min = −0.14 e Å⁻³
220 parameters	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
0 restraints	Extinction coefficient: 0.017 (2)
Primary atom site location: structure-invariant direct methods	Absolute structure: assigned on the basis of known starting material
Secondary atom site location: difference Fourier map

Special details top

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.

Least-squares planes (x,y,z in crystal coordinates) and deviations from them (* indicates atom used to define plane)

- 7.0724 (0.0216) x + 9.3149 (0.0101) y - 2.2196 (0.0144) z = 2.7468 (0.0234)

* 0.0012 (0.0008) O1 * 0.0017 (0.0011) O2 * 0.0013 (0.0008) N1 * -0.0042 (0.0027) C3 0.2866 (0.0047) C1 - 0.2905 (0.0047) C2

Rms deviation of fitted atoms = 0.0024

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 > 2σ(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 (Å²) top

	x	y	z	U_iso*/U_eq
C1	0.60109 (17)	1.0289 (3)	1.0360 (4)	0.0451 (8)
H1	0.6180	1.0100	1.1353	0.054*
C2	0.66484 (18)	0.9896 (3)	0.9279 (3)	0.0433 (8)
H2	0.6900	0.9130	0.9648	0.052*
C3	0.54789 (19)	0.9118 (3)	0.8452 (4)	0.0480 (8)
C4	0.5737 (2)	1.1638 (3)	1.0245 (4)	0.0612 (10)
H4A	0.5586	1.1815	0.9263	0.092*
H4B	0.6159	1.2190	1.0528	0.092*
H4C	0.5291	1.1766	1.0873	0.092*
C5	0.72911 (18)	1.0811 (3)	0.8882 (3)	0.0411 (8)
C6	0.79914 (19)	1.0795 (3)	0.9648 (4)	0.0557 (10)
H6	0.8054	1.0222	1.0401	0.067*
C7	0.8600 (2)	1.1609 (4)	0.9322 (4)	0.0644 (11)
H7	0.9062	1.1596	0.9866	0.077*
C8	0.8522 (2)	1.2433 (4)	0.8204 (4)	0.0616 (10)
H8	0.8933	1.2978	0.7975	0.074*
C9	0.7834 (2)	1.2456 (3)	0.7413 (4)	0.0651 (11)
H9	0.7782	1.3017	0.6646	0.078*
C10	0.7218 (2)	1.1650 (3)	0.7748 (4)	0.0538 (9)
H10	0.6754	1.1673	0.7208	0.065*
C11	0.47944 (19)	0.8982 (3)	1.0836 (4)	0.0497 (9)
C12	0.42713 (19)	0.7910 (3)	1.0310 (4)	0.0531 (9)
H12	0.4052	0.8107	0.9353	0.064*
C13	0.2992 (2)	0.8435 (3)	1.1255 (4)	0.0525 (9)
C14	0.2365 (2)	0.8044 (4)	1.2099 (4)	0.0633 (11)
H14	0.2415	0.7329	1.2673	0.076*
C15	0.1666 (2)	0.8706 (4)	1.2094 (5)	0.0774 (13)
H15	0.1246	0.8436	1.2663	0.093*
C16	0.1586 (3)	0.9763 (4)	1.1254 (5)	0.0811 (13)
H16	0.1112	1.0206	1.1245	0.097*
C17	0.2208 (2)	1.0158 (4)	1.0433 (4)	0.0700 (11)
H17	0.2155	1.0876	0.9867	0.084*
C18	0.2916 (2)	0.9507 (4)	1.0429 (4)	0.0591 (10)
H18	0.3337	0.9791	0.9871	0.071*
C19	0.4742 (2)	0.6684 (3)	1.0253 (4)	0.0710 (11)
H19A	0.4856	0.6409	1.1222	0.106*
H19B	0.5228	0.6821	0.9740	0.106*
H19C	0.4437	0.6053	0.9763	0.106*
N1	0.53871 (15)	0.9397 (2)	0.9892 (3)	0.0462 (7)
O1	0.61905 (12)	0.9558 (2)	0.8006 (2)	0.0493 (6)
O2	0.50324 (15)	0.8593 (2)	0.7646 (3)	0.0645 (7)
O3	0.47462 (14)	0.9432 (2)	1.2024 (3)	0.0683 (7)
O4	0.36534 (14)	0.7686 (2)	1.1322 (3)	0.0626 (7)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
C1	0.0422 (19)	0.0472 (19)	0.0460 (19)	−0.0033 (16)	−0.0029 (15)	−0.0047 (16)
C2	0.0408 (18)	0.0457 (18)	0.0435 (18)	0.0051 (17)	−0.0025 (16)	−0.0019 (16)
C3	0.042 (2)	0.051 (2)	0.051 (2)	0.0015 (18)	−0.0084 (18)	−0.0023 (19)
C4	0.057 (2)	0.054 (2)	0.073 (3)	0.0023 (19)	0.009 (2)	−0.012 (2)
C5	0.0383 (18)	0.0417 (18)	0.0433 (19)	0.0068 (16)	0.0022 (15)	−0.0071 (17)
C6	0.047 (2)	0.058 (2)	0.062 (2)	0.0069 (19)	−0.0058 (19)	0.014 (2)
C7	0.038 (2)	0.075 (3)	0.080 (3)	−0.005 (2)	−0.005 (2)	0.003 (2)
C8	0.048 (2)	0.061 (2)	0.076 (3)	−0.0053 (19)	0.010 (2)	0.000 (2)
C9	0.082 (3)	0.051 (2)	0.062 (3)	−0.007 (2)	−0.001 (2)	0.013 (2)
C10	0.052 (2)	0.0544 (19)	0.055 (2)	−0.0025 (19)	−0.0085 (19)	0.005 (2)
C11	0.041 (2)	0.057 (2)	0.051 (2)	0.0007 (17)	−0.0029 (18)	0.0033 (19)
C12	0.042 (2)	0.057 (2)	0.060 (2)	−0.0032 (18)	−0.0020 (18)	0.0000 (19)
C13	0.046 (2)	0.058 (2)	0.054 (2)	−0.0165 (19)	−0.0003 (18)	−0.007 (2)
C14	0.053 (2)	0.068 (2)	0.069 (3)	−0.021 (2)	0.007 (2)	0.000 (2)
C15	0.049 (2)	0.099 (3)	0.084 (3)	−0.024 (3)	0.015 (2)	−0.021 (3)
C16	0.056 (3)	0.078 (3)	0.109 (4)	0.001 (2)	0.008 (3)	−0.025 (3)
C17	0.065 (3)	0.060 (2)	0.085 (3)	0.003 (2)	0.003 (2)	−0.005 (2)
C18	0.045 (2)	0.061 (2)	0.071 (3)	−0.009 (2)	0.0103 (19)	−0.002 (2)
C19	0.058 (2)	0.059 (2)	0.096 (3)	0.000 (2)	0.001 (2)	0.003 (2)
N1	0.0423 (16)	0.0529 (17)	0.0434 (17)	−0.0035 (14)	−0.0015 (13)	−0.0044 (14)
O1	0.0416 (13)	0.0606 (13)	0.0458 (12)	−0.0018 (12)	0.0011 (11)	−0.0088 (12)
O2	0.0515 (14)	0.0824 (16)	0.0595 (15)	−0.0106 (15)	−0.0097 (12)	−0.0144 (15)
O3	0.0592 (17)	0.0874 (18)	0.0583 (16)	−0.0187 (15)	0.0101 (13)	−0.0113 (16)
O4	0.0437 (14)	0.0670 (16)	0.0770 (18)	−0.0058 (13)	0.0026 (14)	0.0161 (14)

Geometric parameters (Å, º) top

C1—N1	1.483 (4)	C10—H10	0.930
C1—C4	1.511 (5)	C11—O3	1.198 (4)
C1—C2	1.527 (4)	C11—N1	1.400 (4)
C1—H1	0.980	C11—C12	1.522 (5)
C2—O1	1.452 (4)	C12—O4	1.422 (4)
C2—C5	1.504 (4)	C12—C19	1.528 (4)
C2—H2	0.980	C12—H12	0.980
C3—O2	1.198 (4)	C13—O4	1.375 (4)
C3—O1	1.355 (4)	C13—C18	1.377 (5)
C3—N1	1.370 (4)	C13—C14	1.379 (5)
C4—H4A	0.960	C14—C15	1.377 (5)
C4—H4B	0.960	C14—H14	0.930
C4—H4C	0.960	C15—C16	1.371 (6)
C5—C6	1.379 (5)	C15—H15	0.930
C5—C10	1.380 (4)	C16—C17	1.362 (6)
C6—C7	1.378 (5)	C16—H16	0.930
C6—H6	0.930	C17—C18	1.383 (5)
C7—C8	1.360 (5)	C17—H17	0.930
C7—H7	0.930	C18—H18	0.930
C8—C9	1.373 (5)	C19—H19A	0.960
C8—H8	0.930	C19—H19B	0.960
C9—C10	1.384 (5)	C19—H19C	0.960
C9—H9	0.930

N1—C1—C4	111.6 (3)	O3—C11—N1	119.5 (3)
N1—C1—C2	97.9 (2)	O3—C11—C12	123.5 (3)
C4—C1—C2	115.5 (3)	N1—C11—C12	117.0 (3)
N1—C1—H1	110.4	O4—C12—C11	110.1 (3)
C4—C1—H1	110.4	O4—C12—C19	105.2 (3)
C2—C1—H1	110.4	C11—C12—C19	110.3 (3)
O1—C2—C5	110.4 (3)	O4—C12—H12	110.4
O1—C2—C1	102.7 (2)	C11—C12—H12	110.4
C5—C2—C1	119.5 (3)	C19—C12—H12	110.4
O1—C2—H2	107.9	O4—C13—C18	125.5 (3)
C5—C2—H2	107.9	O4—C13—C14	115.2 (3)
C1—C2—H2	107.9	C18—C13—C14	119.3 (4)
O2—C3—O1	122.2 (3)	C15—C14—C13	120.3 (4)
O2—C3—N1	129.2 (3)	C15—C14—H14	119.9
O1—C3—N1	108.7 (3)	C13—C14—H14	119.9
C1—C4—H4A	109.5	C16—C15—C14	120.4 (4)
C1—C4—H4B	109.5	C16—C15—H15	119.8
H4A—C4—H4B	109.5	C14—C15—H15	119.8
C1—C4—H4C	109.5	C17—C16—C15	119.4 (4)
H4A—C4—H4C	109.5	C17—C16—H16	120.3
H4B—C4—H4C	109.5	C15—C16—H16	120.3
C6—C5—C10	118.2 (3)	C16—C17—C18	121.0 (4)
C6—C5—C2	119.2 (3)	C16—C17—H17	119.5
C10—C5—C2	122.6 (3)	C18—C17—H17	119.5
C7—C6—C5	121.4 (3)	C13—C18—C17	119.6 (3)
C7—C6—H6	119.3	C13—C18—H18	120.2
C5—C6—H6	119.3	C17—C18—H18	120.2
C8—C7—C6	119.9 (3)	C12—C19—H19A	109.5
C8—C7—H7	120.1	C12—C19—H19B	109.5
C6—C7—H7	120.1	H19A—C19—H19B	109.5
C7—C8—C9	119.8 (4)	C12—C19—H19C	109.5
C7—C8—H8	120.1	H19A—C19—H19C	109.5
C9—C8—H8	120.1	H19B—C19—H19C	109.5
C8—C9—C10	120.5 (3)	C3—N1—C11	128.1 (3)
C8—C9—H9	119.8	C3—N1—C1	109.9 (3)
C10—C9—H9	119.8	C11—N1—C1	122.0 (3)
C5—C10—C9	120.2 (3)	C3—O1—C2	108.3 (2)
C5—C10—H10	119.9	C13—O4—C12	118.1 (3)
C9—C10—H10	119.9

N1—C1—C2—O1	33.8 (3)	C15—C16—C17—C18	0.3 (6)
C4—C1—C2—O1	−84.8 (3)	O4—C13—C18—C17	178.3 (3)
N1—C1—C2—C5	156.3 (3)	C14—C13—C18—C17	−1.4 (5)
C4—C1—C2—C5	37.7 (4)	C16—C17—C18—C13	0.7 (6)
O1—C2—C5—C6	−148.7 (3)	O2—C3—N1—C11	10.0 (6)
C1—C2—C5—C6	92.6 (4)	O1—C3—N1—C11	−170.9 (3)
O1—C2—C5—C10	29.4 (4)	O2—C3—N1—C1	−167.7 (3)
C1—C2—C5—C10	−89.2 (4)	O1—C3—N1—C1	11.4 (3)
C10—C5—C6—C7	1.4 (5)	O3—C11—N1—C3	−171.2 (3)
C2—C5—C6—C7	179.7 (3)	C12—C11—N1—C3	12.3 (5)
C5—C6—C7—C8	−1.4 (6)	O3—C11—N1—C1	6.2 (5)
C6—C7—C8—C9	0.6 (6)	C12—C11—N1—C1	−170.2 (3)
C7—C8—C9—C10	0.2 (6)	C4—C1—N1—C3	93.1 (3)
C6—C5—C10—C9	−0.6 (5)	C2—C1—N1—C3	−28.4 (3)
C2—C5—C10—C9	−178.8 (3)	C4—C1—N1—C11	−84.8 (4)
C8—C9—C10—C5	−0.2 (5)	C2—C1—N1—C11	153.7 (3)
O3—C11—C12—O4	9.6 (5)	O2—C3—O1—C2	−168.2 (3)
N1—C11—C12—O4	−174.1 (3)	N1—C3—O1—C2	12.6 (3)
O3—C11—C12—C19	−106.0 (4)	C5—C2—O1—C3	−158.8 (2)
N1—C11—C12—C19	70.3 (4)	C1—C2—O1—C3	−30.3 (3)
O4—C13—C14—C15	−178.6 (3)	C18—C13—O4—C12	−9.8 (5)
C18—C13—C14—C15	1.1 (5)	C14—C13—O4—C12	169.9 (3)
C13—C14—C15—C16	−0.1 (6)	C11—C12—O4—C13	82.5 (3)
C14—C15—C16—C17	−0.6 (6)	C19—C12—O4—C13	−158.7 (3)

Acknowledgements

We are grateful to the EPSRC and Queen Mary, University of London for a studentship to YY, the Royal Society and the University of London Central Research Fund for their financial support to JE, and the EPSRC National Mass Spectrometry Service (Swansea) for accurate mass determination.

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