Synthesis and X-ray crystal structure analysis of 1,4-epoxy-4-methyl-1H,4H- 2,3-benzodioxepin

Article abstract of DOI:10.1515/znb-2011-0412

Ozonolysis of 2-methyl-1H-indene (1) afforded the stable secondary ozonide 1,4-epoxy-4-methyl-1H,4H-2,3-benzodioxepin (2). This compound crystallizes in two polymorphic forms, depending on the solvent used. The monoclinic form 2a containing two symmetry-independent molecules (enantiomers) is obtained by crystallization from dichloromethane. In contrast, the orthorhombic modification 2b is obtained from ethyl acetate solution and crystallizes as a conglomerate of enantiomerically pure single crystals. Additionally, the ring-opened product 2-(2-oxopropyl)benzoic acid (3) was obtained and investigated by X-ray crystal structure analysis.

Full text of DOI:10.1515/znb-2011-0412

Synthesis and X-Ray Crystal Structure Analysis of 1,4-Epoxy-4-methyl-
H,4H-2,3-benzodioxepin
1
a
a
b
a
David S. Giera , Lothar Hennig , Thomas Gelbrich , and Christoph Schneider
a
b
Institut f u¨ r Organische Chemie, Universit a¨ t Leipzig, Johannisallee 29, 04103 Leipzig, Germany
Institute of Pharmacy, University of Innsbruck, Innrain 52, 6020 Innsbruck, Austria
Reprint requests to M. Sc. D. S. Giera. E-mail: david.giera@chemie.uni-leipzig.de
Z. Naturforsch. 2011, 66b, 419 – 424; received October 7, 2010 / revised November 30, 2010
Ozonolysis of 2-methyl-1H-indene (1) afforded the stable secondary ozonide 1,4-epoxy-4-methyl-
1H,4H-2,3-benzodioxepin (2). This compound crystallizes in two polymorphic forms, depending on
the solvent used. The monoclinic form 2a containing two symmetry-independent molecules (enan-
tiomers) is obtained by crystallization from dichloromethane. In contrast, the orthorhombic modifica-
tion 2b is obtained from ethyl acetate solution and crystallizes as a conglomerate of enantiomerically
pure single crystals. Additionally, the ring-opened product 2-(2-oxopropyl)benzoic acid (3) was ob-
tained and investigated by X-ray crystal structure analysis.
Key words: Ozonolysis, Stable Secondary Ozonide, X-Ray Crystal Structure Analysis
Introduction
ozonide derived from 1,2,3,6b,7,8-hexahydrobenzo[j]-
fluoranthene [11a] and of 3-methoxycarbonyl-5-anis-
yl-1,2,4-trioxacyclopentane [11b] have been reported.
The positions of the peroxide and ether bridges in the
latter structure are affected by disorder, so that the in-
teratomic distances and bond angles in this part of the
molecule are probably not very reliable. Herein, we
report on the synthesis and crystal structure of 1,4-
epoxy-4-methyl-1H,4H-2,3-benzodioxepin (2), one of
the simplest indene-derived secondary ozonides.
Since the early investigations of the oxidative cleav-
age of unsaturated compounds with ozone by Har-
ries [1] and Staudinger [2], much effort has been
dedicated to studies of the actual mechanism of the
ozonolysis [3]. According to the widely accepted
Criegee mechanism [4], the formation of ozonides
(
1,2,4-trioxolanes) [5] can be considered the result
of a series of three [2+3]-cycloaddition or cyclore-
version reactions [6]. The two intermediates, primary
ozonide (1,2,3-trioxolane) and carbonyl oxide, have
limited lifetimes and are converted into the more sta-
ble secondary ozonide, which can be subjected to
a hydrolytic, reductive or oxidative workup, giving
rise to different products. Particularly ozonides of cy-
clopentenes [7a] and indenes [7b– c, 8, 9], and their
respective derivatives show extraordinary stability. Re-
cently, Jung et al. reported the formation of dio-
zonides, triozonides and tetraozonides by ozonolysis
of substituted 2-cyclohexenones, followed by treat-
ment with O-methyl-hydroxylamine and subsequent
co-ozonolysis with different carbonyl compounds [10].
Some secondary ozonides are remarkably stable, but
crystal structures are known for only a few compounds
of this class [9, 11]. These include two secondary
ozonides derived from highly substituted indenes [9a]
and two derived from indenones [9b – e]. Furthermore,
Results and Discussion
◦
Ozonolysis of 2-methyl-1H-indene (1) at −78 C
in dichloromethane afforded 1,4-epoxy-4-methyl-
1
H,4H-2,3-benzodioxepin (2) in 62 % yield (Sche-
me 1). The crystalline product has a melting point of
4
◦
5 C and shows remarkable stability. An excess of
dimethyl sulfide reduces it rather slowly, and it can be
stored, without decomposition, at ambient temperature
for several months. Similar observations have been
made previously on related compounds [8b, 8e].
the crystal structures of a rather complex polycyclic Scheme 1. Ozonolysis of 2-methyl-1H-indene.
0
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420
D. S. Giera et al. · 1,4-Epoxy-4-methyl-1H,4H-2,3-benzodioxepin
2
a
2b
C10H10O3
178.18
3
Table 1. Crystal structure data of 2 and 3.
Formula
Mr
C10H10O3
178.18
C10H10O3
178.18
T, K
213(2)
120(2)
213(2)
3
Crystal size, mm
Crystal system
Space group
0.3×0.2×0.1
monoclinic
P21
8.2047(8)
19.483(2)
5.4849(5)
102.30(1)
856.6(1)
4
0.21×0.18×0.06
orthorhombic
P212121
8.9444(3)
18.6915(6)
5.1152(2)
90
855.16(4)
4
1.38
0.2×0.2×0.08
monoclinic
P21/c
11.822(5)
6.9490(8)
11.597(6)
110.46(4)
892.6(6)
4
˚
a, A
˚
b, A
˚
c, A
◦
β,
˚
3
V, A
Z
−
3
Dcalcd, g cm
µ(MoKα ), mm
F(000), e
1.38
0.1
376
1.33
0.1
376
−
1
0.1
376
hkl range
−10 ≤ h ≤ 10
−11 ≤ h ≤ 9
−21 ≤ k ≤ 17
−6 ≤ l ≤ 5
5061
1609 / 0.0216
158
0.0292
0.0796
1.075
0.18 / −0.18
−14 ≤ h ≤ 14
−6 ≤ k ≤ 8
−3 ≤ l ≤ 12
2099
1128 / 0.1024
309
0.0508
0.1460
0.692
0.01 / 0.0
a
b
2
2
R1 = ΣꢀFo|−|Fcꢀ/Σ|Fo|; wR2 = [Σw(Fo
−
−
−
23 ≤ k ≤ 23
6 ≤ l ≤ 6
2
2
2
2 1/2
2
2
Fc ) /Σw(Fo ) ] , w = [σ (Fo ) + (AP) +
BP]
−1
2
2
, where P = (Max(Fo ,0) + 2Fc )/3
Refl. measured
6132
and A and B are constants adjusted by the pro-
Refl. unique / Rint
Param. refined a
R1 [I ≥ 2σ(I)]
3234 / 0.0540
315
gram; c GoF = S = [Σw(Fo − Fc ) /(nobs −
2
2 2
1/2
nparam)] , where nobs is the number of data and
d
0.0386
d
nparam the number of refined parameters; final
b
d
wR2 (all data)
0.0988
R values for the alternative refinement in space
group P21/a: R1 [I ≥ 2σ(I)] = 0.067 and wR2
2
c
GoF (F )
ρfin (max / min), e A
0.912
0.17 / −0.15
˚
−3
∆
(all data) = 0.1838.
Fig. 1 (color online). Two and three bond coupling in HMBC
spectra of ozonide 2.
The structure of the product was confirmed by
spectroscopic methods and by X-ray crystallogra-
phy. A complete NMR assignment was made by Fig. 2. Molecules A (left) and B (right) of the monoclinic
1
13
form 2a.
use of H,
C, APT, H,H-COSY, HSQC and
HMBC spectra. Most importantly, the bridgehead-
dichloromethane solution (see Table 1). Its two crys-
tallographically independent molecules (enantiomers),
labelled A and B, are depicted in Fig. 2. The or-
thorhombic modification 2b (Fig. 4) crystallizes from
ethyl acetate and contains one independent homochiral
molecule.
1
13
proton ( H: 6.33 ppm; C(APT): 101.52 ppm) gives
cross correlation peaks to the quaternary OCO car-
bon (107.97 ppm), the quaternary aromatic car-
bons (133.41 and 131.62 ppm) and an aromatic CH
(
125.27 ppm) via two and three bond coupling in the
HMBC spectrum (Fig. 1).
Form 2a crystallizes in the space group P2 . Its
1
two independent molecules are related by a pseudo-
inversion center, so that the overall molecular arrange-
X-Ray crystal structure analyses
The ozonide 2 crystallizes in two polymorphic ment exhibits P2 /a pseudo-symmetry. In order to test
1
forms. The monoclinic form 2a is obtained from the correctness of the assigned space group, the final
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D. S. Giera et al. · 1,4-Epoxy-4-methyl-1H,4H-2,3-benzodioxepin
421
˚
Table 2. Bond lengths (A) and angles (deg) for the 1,2,4-tri-
oxolane moieties of 2a and 2b with estimated standard devi-
ations in parentheses.
2
a (Molecule A)
1.477(4)
1.451(5)
1.437(4)
1.424(5)
1.411(5)
1.508(5)
1.512(5)
1.380(5)
1.497(4)
2a (Molecule B)
1.470(4)
1.446(5)
1.408(4)
1.430(4)
1.416(4)
1.513(5)
1.502(5)
1.401(5)
1.491(4)
2b
O1–O2
1.479(1)
1.472(2)
1.419(2)
1.430(2)
1.412(2)
1.517(3)
1.512(2)
1.397(2)
1.509(2)
C1–O2
C1–O3
C5–O1
C5–O3
C1–C2
C2–C3
C3–C4
C4–C5
O2–C1–O3
O2–C1–C2
C1–C2–C3
C2–C3–C4
C3–C4–C5
C4–C5–O1
C4–C5–O3
O1–C5–O3
103.3(3)
110.2(3)
111.6(3)
119.2(3)
117.8(3)
111.9(3)
110.7(3)
103.5(3)
104.1(3)
108.2(3)
111.6(3)
118.2(3)
117.8(3)
113.0(3)
111.1(3)
102.1(2)
103.6(1)
108.1(1)
110.9(1)
119.2(1)
117.4(1)
111.5(1)
111.6(1)
102.6(1)
Fig. 3. XPAC plot (see ref. [13]) illustrating a geomet-
rical comparison of the environments of the independent
molecules A and B of form 2a.
ꢁ
P2 (Z = 2) structure model was transformed into
1
ꢁ
the corresponding P2 /a (Z = 1) setting and then
1
encircled area). Hence, the environments of A and B
are clearly distinct from one another. In conclusion, the
geometrical analysis with XPAC supports the choice of
P2 over P2 /a as the correct space group symmetry
re-refined. This alternative structure refinement gave
significantly higher R values (see footnotes of Table
1
). Moreover, freely refined positional and isotropic
1
1
displacement parameters of the H atoms were found
of 2a.
to be considerably more consistent in the P2 model
1
As described above, molecules A and B of form
a have very similar geometries (see Table 2). The
Cremer-Pople puckering parameters [14] calculated
(
0.033 ≤ U (H) ≤ 0.092) than in the P2 /a alterna-
iso
1
2
tive (0.045 ≤ U (H) ≤ 0.142). A closer inspection
iso
of the data for 2a has shown that one third of all
h0l reflections are observed and that their intensities,
even though they are weak, are significant. This indi-
for the five-membered rings in molecules A [Q2 =
˚
◦
˚
0
.440(2) A, ϕ2 = 127.2(3) ] and B [Q2 = 0.452(3) A,
◦
ϕ2 = 127.1(3) ] of form 2a indicate a twist conforma-
tion.
cates a (non-centrosymmetric) P2 structure with an a-
1
glide as a pseudo-symmetry element, whereas the cen-
The corresponding parameters for the orthorhom-
reflections with h = 2n+1 to be systematically absent. bic polymorph 2b are very similar: Q2 = 0.451(1) A
trosymmetric P2 /a alternative would require all h0l
1
˚
◦
and ϕ2 = 129.3(2) . The six-membered rings with the
atoms O3, C1, C2, C3, C4 and C5 adopt an envelope
conformation in both independent molecules (A and B)
of the form 2a. As expected, the bond lengths and an-
gles in the orthorhombic form 2b (Fig. 4) are in concert
with the values found in the monoclinic form 2a (see
Table 2).
The program XPAC [12] was used to investi-
gate topological differences between the independent
molecules A and B of structure 2a by comparing the
geometries of their respective environments contain-
ing 14 surrounding molecules. Using a previously de-
scribed approach [13], individual similarity indices xi
were calculated for 91 molecular pairs using all 13
non-H positions. The diagram in Fig. 3 illustrates that
The bond lengths and angles of the 1,2,4-trioxolan
certain xi values deviate significantly from 0. These fragment of compound 2 are in good agreement with
data are the result of an increase of the angular differ- previously reported bond parameters of secondary
ences between the two packing arrangements, and the ozonides [9, 11].
overall XPAC index X is 1.5. Additionally, a set of dis-
An attempt to crystallize the ozonide 2 from toluene
tance parameters δ was obtained by calculating the resulted in a rearrangement to the ring-opened product
d,i
distance between two molecular centroids in the cluster 3 (Fig. 5), which was possibly due to an intramolec-
around molecule A and comparing these with the cor- ular redox reaction [15]. The obtained single crystals
responding distance in the cluster of B. Remarkably, a were investigated by X-ray structure analysis, and the
˚
subset of δd,i values is found in the 0.3 A range (Fig. 3, essential bond parameters of 3 are listed in Table 3.
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422
D. S. Giera et al. · 1,4-Epoxy-4-methyl-1H,4H-2,3-benzodioxepin
˚
Table 3. Selected bond lengths (A) and angles (deg) for 3
a
with estimated standard deviations in parentheses .
C1–O1
C2–O3
C4–C5
C6–C7
C8–C9
C9–C10
1.271(8)
1.408(8)
1.371(9)
1.400(7)
1.519(8)
1.509(9)
C1–O2
C3–C4
C5–C6
C7–C8
C9–O3
1.315(8)
1.411(8)
1.382 (9)
1.523(9)
1.242(9)
O1–C1–O2
O2–C1–C2
C1–C2–C7
C3–C4–C5
C5–C6–C7
C6–C7–C8
C8–C9–O3
121.6(5)
115.9(7)
123.4(6)
118.1(7)
122.9(6)
118.9(6)
120.8(7)
O1–C1–C2
C1–C2–C3
C2–C3–C4
C4–C5–C6
C6–C7–C2
C7–C8–C9
C8–C9–C10
122.5(6)
117.5(5)
122.0(6)
120.5(6)
117.6(6)
115.8(6)
115.7(7)
Fig. 4. Molecular structure of the orthorhombic form 2b.
i
O2–H2
O2–O1A
0.82
2.667(5)
O1 · H2
1.86
i
◦
O2 –H2 ···O1
166.3
a
Symmetry operation: (i) −x+1, −y, −z+2.
Fig. 5. Molecular structure of 3.
i
The crystal structure is composed of O2–H2···O1 -
bonded dimers [(i) –x+1, –y, –z+2], where the center
of the eight-membered ring coincides with a crystallo-
graphic center of symmetry (Fig. 6).
Conclusion
The synthesis of 1,4-epoxy-4-methyl-1H,4H-2,3-
benzodioxepin (2) and its structural characterization
by spectroscopic methods and X-ray crystallography
has been described. In contrast to previously reported,
Fig. 6. Dimeric structure of 3.
t (triplet), q (quartet), p (pentet) and m (multiplet). Melt-
ing points were determined on a Boetius hot-stage micro-
highly substituted indene-derived ozonides, compound scope. IR spectra were obtained with an FTIR spectrometer
2
has a rather simple structure, but its stability is sim- (Genesis ATI Mattson/Unicam). UV spectra were recorded
ilar to that of the other compounds. The ring-opened on a UV spectrometer (DU-650 Beckmann). ESI mass spec-
product 2-(2-oxopropyl)benzoic acid (3) was also ob- tra were recorded on a Bruker APEX II FT-ICR. Flash col-
tained and characterized by X-ray crystallography.
umn chromatography was performed using Merck silica gel
60 230 – 400 mesh (0.040 – 0.063 mm).
Experimental Section
1,4-Epoxy-4-methyl-1H,4H-2,3-benzodioxepin (2)
1H and 13C NMR spectra were recorded in CDCl so-
3
lutions, using a Varian Mercury plus 400 MHz spectrom-
A solution of 2-methyl-1H-indene (98 %, 1.134 g,
eter. The signals were referenced to residual chloroform 8.54 mmol) in 20 mL absolute dichloromethane was cooled
1
13
◦
(
7.26 ppm, H, 77.16 ppm, C). Chemical shifts are reported to −78 C and subsequently treated with ozone until the solu-
in ppm, multiplicities are labelled s (singulett), d (doublet), tion became blue in color (20 min). The solvent was removed
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D. S. Giera et al. · 1,4-Epoxy-4-methyl-1H,4H-2,3-benzodioxepin
423
in vacuo, and the residue was purified by silica gel chro- and 3 were measured on an IPDS1 diffractometer (Fa. Stoe);
matography (petroleum ether/diethyl ether, 6 : 1 → 5 : 1) to the data for 2b were collected on a Bruker P4 diffractometer.
afford 948.2 mg (62 %; 5.32 mmol) of 1,4-epoxy-4-methyl- The relevant crystallographic data are listed in the Table 1.
1
H,4H-2,3-benzodioxepin (2) as a yellowish solid. M. p.
The structures were determined using the Direct Methods
◦
45 C. – UV/Vis (MeCN): λmax(lg εmax) = 214 nm (3.869). – procedure in SHELXS-97 and refined by full-matrix least-
2
IR (KBr): ν˜ = 3417, 3056, 2989, 2936, 1720, 1608, 1586, squares on F using SHELXL-97 [16]. All non-hydrogen
1
1
8
4
490, 1459, 1425, 1383, 1346, 1287, 1272, 1212, 1193, atoms were refined anisotropically. The hydrogen atoms of
174, 1108, 1094, 1054, 1028, 953, 943, 923, 906, 872, 2b were located in a difference Fourier map and refined
64, 840, 827, 783, 755, 723, 657, 638, 608, 559, 501, 449, isotropically. In the case of 2a and 3, all hydrogen atoms were
−1
1
◦
26 cm . – H NMR (400 MHz, CDCl , 26 C): δ = 1.79 placed in calculated positions with their isotropic U values
3
(
s, 3 H, CH ), 3.10 (d, J = 17.4 Hz, 1 H, CH ), 3.27 (d, set to 1.2 or 1.5 Ueq of the parent C or O atom. Refinements
3
2
J = 17.4 Hz, 1 H, CH ), 6.33 (s, 1 H, CH), 7.18 (m, 1 of the Flack x parameter for 2a/b were not deemed necessary
2
H, Har), 7.23 – 7.25 (m, 2 H, Har), 7.36 (m, 1 H, Har). – because all atoms are only very weak anomalous scatterers
1
3
◦
C NMR (100 MHz, CDCl , 26 C): δ = 22.0 (CH ), 39.3 and because of the pseudo-centrosymmetry of 2a. In the case
3
3
(
1
CH ), 101.5 (CH), 108.0 (Cq), 125.3, 126.5, 128.6, 129.8, of compound 3, a significant number of reflections affected
2
+
31.6, 133.4 (all Car). – MS (ESI): m/z = 179 [M+H] , 185 by twinning were eliminated during the integration, resulting
+
+
[
M+Li] , 201 [M+Na] .
in a relatively low data/parameter ratio of the corresponding
structure refinement.
CCDC 795613 (2a), 795451 (2b) and 795450 (3) contain
the supplementary crystallographic data for this paper. These
data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk
X-Ray structure determination
A sealed vial, containing a solution of 50 mg 1,4-epoxy-
4-methyl-1H,4H-2,3-benzodioxepin (2) in 0.2 mL of the re-
/
data request/cif.
spective solvent, was kept at ambient temperature for several
days. Single crystals were obtained by slow evaporation of
the solvent. Crystallization from dichloromethane gave the
monoclinic form 2a, while from ethyl acetate the orthorhom-
Acknowledgement
We would like to thank Prof. Dr. J. Sieler (University of
bic form 2b was obtained. Intensity data for compounds 2a Leipzig) for his support.
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