(E)-6-methoxy-3-(a-methoxybenzyl-idene)benzo[b]furan-2(3H)-one at 173 K

Article abstract of DOI:10.1107/S0108270100000731

Isoaurones [3-arylidenebenzofuran-2(3H)ones] were a unique class of flavonoid compounds isomeric with aurones [2-arylidenebenzofuran-3(2H)-ones], some of which are naturally occurring, such as E-marginalin. The furanone ring of the compound was fused to a methoxybenzene ring system, as it was planar in nature. The molecules in the crystal of the compound were packed together via intermolecular C-H---O interactions and stacking between the benzofuranone ring systems.

Full text of DOI:10.1107/S0108270100000731

organic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
We have determined on the basis of the following X-ray
crystallographic analysis that the novel isoaurone compound,
(II), has the E-con®guration. This result clearly indicates that
the glycolic acid product, (I), possesses the (2R,3R) [or
(2S,3S)] con®guration, if the dehydration step leading to the
isoaurone (II) occurs by the expected concerted anti-
periplanar E2 elimination reaction at (I). In the original paper
ISSN 0108-2701
(E)-6-Methoxy-3-(a-methoxybenzyl-
idene)benzo[b]furan-2(3H)-one at
173 K
Anthony J. Burke,a² Helmut W. Schmalle,b* Bernard A.
Bradya³ and W. Ivo O'Sullivana
aDepartment of Chemistry, University College, Belfield, Dublin 4, Ireland, and
bInstitute of Inorganic Chemistry, University of Zurich, Winterthurerstrasse 190,
È
CH-8057 Zurich, Switzerland
È
Correspondence e-mail: schmalle@aci.unizh.ch
Received 30 November 1999
Accepted 17 January 2000
reporting the synthesis of (I) as the result of a benzilic acid
rearrangement on 1-(2-hydroxy-4-methoxyphenyl)-3-meth-
oxy-3-phenylpropan-1,2-dione (Brady et al., 1989), compound
(I) was assigned the (2R,3S)-con®guration on the basis of a
mechanistic postulate. At present the mechanism of this
reaction is being re-evaluated. In the original paper (Brady et
al., 1989) the diagram clearly shows that the glycolic acid
product had the (2R,3S)-con®guration, but it was inad-
vertently named (2R,3R) in the text. This error was carried
over into our subsequent paper (Burke & O'Sullivan, 1997).
The furanone ring of the title compound, (II), which is
essentially planar, is fused to a methoxybenzene ring system.
Both ring systems are approximately coplanar, the angle
between the furanone moiety and the fused benzene ring
being 175.7 (1)ꢁ. Selected bond lengths and angles in Table 1
show that the benzene ring C4±C9 has a remarkable amount
of angle strain arising from the ring fusion. The internal bond
angles [C7 115.8 (1), C8 124.7 (1), C9 118.5 (1) and C4
118.9 (1)ꢁ] are all somewhat different from 120.0ꢁ, whereas the
vinylic phenyl ring has internal angles between 119.7 (1) and
120.2 (1)ꢁ. In accordance with an earlier nuclear Overhauser
effect experiment, the present X-ray experiment shows the
The title compound, C17H14O4, is an unprecedented new
synthetic isoaurone-type enol ether that has the E con®gura-
tion. The planar furanone ring is fused to a methoxybenzene
ring system, with an interplanar angle of 175.7 (1)ꢁ. Due to this
ring fusion, the six-membered ring has a signi®cant amount of
ring strain, as shown by the internal ring angle range of
115.8 (1)±124.7 (1)ꢁ, whereas the vinylic phenyl ring has
internal angles between 119.7 (1) and 120.2 (1)ꢁ. The mol-
ecules form in®nite hydrogen-bonding layers along the b
direction of the form CÐHÁ Á ÁO, where the keto O atom acts
as a bifurcated acceptor. These layers are connected along the
c direction by another hydrogen bond with a methoxy H atom
as donor. In addition to this connection, the layers are stacked
via centres of symmetry by a pair of symmetry-related
benzofuranone ring systems.
Comment
Isoaurones [3-arylidenebenzofuran-2(3H)ones] are an un-
common class of ¯avonoid compounds isomeric with aur-
ones [2-arylidenebenzofuran-3(2H)-ones], some of which are
naturally occurring, e.g. E-marginalin (Barbier, 1987). Like the
aurones, isoaurones can exist in either the E or the Z form.
This class of compound has been of synthetic interest over the
years (Gripenberg & Juselius, 1954; Walter et al., 1966;
Moriarty et al., 1984; Litinas & Stampelos, 1992; Rossi et al.,
1995). In the course of our studies in the ¯avonoid ®eld we
have synthesized the unusual title isoaurone-type enol ether
compound, (II) (Burke & O'Sullivan, 1997) via lactonization
and subsequent dehydration of (2R,3R)-2-hydroxy-2-(2-
hydroxy-4-methoxyphenyl)-3-methoxy-3-phenylpropan-1-oic
acid, (I).
Figure 1
Â
² Current address: Departamento de Quõmica, Universidade de Evora,
PLATON (Spek, 1990) displacement ellipsoid plot of (II) at the 50%
probability level with the atom-numbering scheme. H atoms are drawn as
small spheres of arbitrary radii.
Â
Colegio Luõs Antonio Verney, Rua RomaÄo Ramalho 59, 7000 Evora, Portugal.
Â
Â
³ Current address: Avondale Chemical Co., Rathdrum, Co. Wicklow, Ireland.
Â
ꢀ
484 # 2000 International Union of Crystallography
Printed in Great Britain ± all rights reserved
Acta Cryst. (2000). C56, 484±486

organic compounds
anhydride (10 ml) was heated under re¯ux for 2 h. The cooled
solution was poured into iced water (30 ml). The resulting yellow
solid was collected and crystallized from ethanol as green±yellow
elongated plates of (II) (yield 0.079 g, 30%; m.p. 435±437 K).
Analysis, found: C 72.05, H 5.01%; C17H14O4 requires: C 72.32, H
5.01%; IR (ꢀmax, KBr, cm 1): 1762, 1626 and 1587; (ꢁmax, 95%
1
EtOH, nm): 206.1 (" dm 3 mol 1 cm 23, 709), 233.2 (13, 923),
256.6 (11, 895) and 342 (13, 861); 1H NMR (270 MHz, CDCl3,
p.p.m.): 3.71 (s, 3H), 3.83 (s, 3H), 6.66 (d, J = 2.2 Hz, 1H), 6.70 (dd, J
= 8.2, 2.4 Hz, 1H), 7.41 (m, 2H), 7.52 (m, 3H), and 7.70 (d, J = 8.2 Hz,
1H); 13C NMR (67.80 MHz, CDCl3, p.p.m.): 55.63, 57.72, 96.63,
103.18, 109.19, 116.82, 123.87, 128.74, 128.99, 130.32, 130.56, 152.56,
159.95, 168.02 and 168.21; MS (EI) m/z: 282.1 (M+, 100), 267.1 (23),
239.1 (50), 211.1 (3) and 105 (50%). Evaporation of the ®ltrate
to half its volume yielded cubes of (3R)-3-acetoxy-6-methoxy-3-
[(R)-methoxyphenylmethyl]benzo[b]furan-2(3H)-one, (III) (yield
0.129 g, 40%; m.p. 409±411 K). Analysis, found: C 66.94, H 5.35%;
C19H18O6 requires: C 66.66, H 5.30%; IR (ꢀmax, KBr, cm 1): 1821,
1752 and 1635; 1H NMR (270 MHz, CDCl3, p.p.m.): 2.03 (s, 3H), 3.24
(s, 3H), 3.79 (s, 3H), 4.78 (s, 1H), 6.14 (d, 8.2 Hz, 1H), 6.46 (dd, J =
8.2, 2.3 Hz, 1H), 6.71 (d, J= 2.3 Hz, 1H), 7.32 (m, 2H) and 7.42 (m,
3H); 13C NMR (67.80 MHz, CDCl3, p.p.m.): 20.37, 55.55, 57.72,
79.33, 83.93, 97.28, 109.29, 113.70, 126.02, 127.90, 128.51, 128.81,
134.5, 156.30, 162.05, 168.45 and 173.84; MS (EI) m/z: 342 (M+, 1),
282 (3), 252 (4), 209 (5), 165 (2) and 121 (100%). An alternative
synthesis of (II) proceeds as follows: a mixture of 3-benzoyl-6-
methoxybenzofuran-2-one, (IV) (0.076 g, 0.284 mmol; Brady, Burke
& O'Sullivan, unpublished results), dimethyl sulfate (0.1 ml,
1.06 mmol), anhydrous potassium carbonate (3 g, 21.7 mmol) and
dry acetone (20 ml) heated under re¯ux for 2 h. The cooled mixture
is then ®ltered free of inorganic matter and diluted with ice and
water. The resulting precipitate crystallizes from ethanol as green±
yellow elongated plates of (II) (yield 0.05 g, 62%; m.p. 436 K). All
the chiral compounds discussed or shown in this paper existed as
racemic mixtures; only one member of the enantiomeric pair is
mentioned in each case for the sake of convenience.
Figure 2
PLUTON (Spek, 1991) packing diagram for (II) exhibiting the layered
structure along b and the stacking of the layers via centres of symmetry.
The hydrogen bonds are shown as dashed lines.
Ê
large distance of 3.703 (16) A between H4 and the C12 methyl
of the vinylic methoxyl group (Fig. 1). It is also worth obser-
ving that the vinylic phenyl group is rotated out of the plane
with the benzofuranone moiety by 78.8 (1)ꢁ. This had already
been predicted using Dreiding molecular models. Some
prominent torsion angles are also shown in Table 1.
The molecules in the crystal of (II) are packed together via
intermolecular CÐHÁ Á ÁO interactions and stacking between
the benzofuranone ring systems. If we consider the intra-
molecular hydrogen bond C4ÐH4Á Á ÁO10 and the inter-
molecular hydrogen bond C4ÐH4Á Á ÁO2(x, y 1, z), then H4
has a bifurcated donor function. With the intermolecular
C12ÐH123Á Á ÁO2(x, y 1, z) bond the keto oxygen O2 is a
bifurcated acceptor. The above mentioned hydrogen bonds
form discrete layers along b. The view along the b axis (Fig. 2)
shows that these layers are connected along the c direction via
another intermolecular hydrogen bond, C11ÐH112Á Á ÁO6( x,
Crystal data
3
C17H14O4
Mr = 282.28
Monoclinic, P21=c
Ê
a = 10.5235 (8) A
Dx = 1.396 Mg m
Mo Kꢃ radiation
Cell parameters from 8000
re¯ections
ꢄ = 2.7±30.3ꢁ
ꢅ = 0.100 mm
T = 173 (1) K
Ê
b = 7.1136 (3) A
1
Ê
c = 18.2587 (13) A
ꢂ = 100.632 (9)ꢁ
V = 1343.38 (15) A
Z = 4
3
Ê
Plate, green±yellow
0.54 Â 0.35 Â 0.06 mm
Data collection
Stoe IPDS diffractometer
' oscillation scans
Absorption correction: numerical
(Coppens et al., 1965)
Tmin = 0.948, Tmax = 0.994
13 623 measured re¯ections
3849 independent re¯ections
2237 re¯ections with I > 2ꢆ(I)
Rint = 0.037
ꢄmax = 30.29ꢁ
1
2
1
2
+ y,
z), where the methoxy H atom acts as a donor.
h = 14 ! 14
Details of the hydrogen bonding system are given in Table 2.
Furthermore, stacking of the benzofuranone moieties is also
displayed in Fig. 2. The stacking follows the [201] direction;
the distance between the centres of gravity of the rings is
k = 0 ! 9
l = 0 ! 25
Between 50 and 200 standard
re¯ections every image
frequency: 6 min
intensity decay: none
Ê
3.672 (1) A.
Re®nement
Re®nement on F2
R[F2 > 2ꢆ(F2)] = 0.034
wR(F2) = 0.067
S = 1.012
3849 re¯ections
246 parameters
All H-atom parameters re®ned
w = 1/[ꢆ2(Fo2) + (0.02P)2]
where P = (Fo2 + 2Fc2)/3
(Á/ꢆ)max = 0.001
Experimental
Compound (II) was prepared as follows: a mixture of (2R,3R)-2-
hydroxy-2-(2-hydroxy-4-methoxyphenyl)-3-methoxy-3-phenylprop-
an-1-oic acid, (I) (0.3 g, 0.94 mmol; Brady et al., 1989), and acetic
3
Ê
Áꢇmax = 0.22 e A
3
Ê
0.19 e A
Áꢇmin
=
ꢀ
Acta Cryst. (2000). C56, 484±486
Anthony J. Burke et al. C17H14O4 485

organic compounds
Table 1
Selected geometric parameters (A, ).
The positions of the H atoms were determined from difference
electron-density maps and they were re®ned with isotropic displa-
cement parameters. The CÐH bond lengths range between 0.960 (15)
ꢁ
Ê
O1ÐC8
O1ÐC2
C2ÐO2
C2ÐC3
C3ÐC10
C3ÐC9
O6ÐC6
O6ÐC11
C4ÐC9
1.3905 (16)
1.4024 (14)
1.1993 (15)
1.4644 (18)
1.3550 (16)
1.4605 (17)
1.3733 (14)
1.4273 (18)
1.3883 (18)
C4ÐC5
C5ÐC6
C6ÐC7
C7ÐC8
C8ÐC9
C10ÐO10
C10ÐC13
O10ÐC12
1.3885 (16)
1.4007 (18)
1.3860 (19)
1.3781 (16)
1.3857 (17)
1.3426 (15)
1.4879 (17)
1.4447 (15)
Ê
and 1.062 (15) A.
Data collection: IPDS Software (Stoe & Cie, 1999); cell re®ne-
ment: IPDS Software; data reduction: IPDS Software; program(s)
used to solve structure: SHELXS97 (Sheldrick, 1990); program(s)
used to re®ne structure: SHELXL97 (Sheldrick, 1997); molecular
graphics: PLATON (Spek, 1990) and PLUTON (Spek, 1991); soft-
ware used to prepare material for publication: SHELXL97.
AJB would like to thank EOLAS (the Irish Science and
Technology research agency) for ®nancial support.
C8ÐO1ÐC2
O2ÐC2ÐO1
O2ÐC2ÐC3
O1ÐC2ÐC3
C10ÐC3ÐC9
C10ÐC3ÐC2
C9ÐC3ÐC2
C6ÐO6ÐC11
C9ÐC4ÐC5
C4ÐC5ÐC6
O6ÐC6ÐC7
O6ÐC6ÐC5
107.67 (9)
C7ÐC6ÐC5
C8ÐC7ÐC6
C7ÐC8ÐC9
C7ÐC8ÐO1
C9ÐC8ÐO1
C8ÐC9ÐC4
C8ÐC9ÐC3
C4ÐC9ÐC3
O10ÐC10ÐC3
O10ÐC10ÐC13
C3ÐC10ÐC13
C10ÐO10ÐC12
121.57 (11)
115.81 (11)
124.66 (12)
123.08 (11)
112.21 (10)
118.49 (11)
105.97 (11)
135.32 (11)
115.77 (11)
120.71 (10)
123.52 (12)
120.41 (10)
119.04 (11)
133.17 (11)
107.77 (10)
129.73 (12)
123.86 (11)
106.33 (10)
116.80 (11)
118.87 (11)
120.59 (12)
123.42 (11)
115.00 (12)
Supplementary data for this paper are available from the IUCr electronic
archives (Reference: JZ1387). Services for accessing these data are
described at the back of the journal.
References
Barbier, M. (1987). Liebigs Ann. Chem. pp. 545±546.
Brady, B. A., Geoghegan, M. & O'Sullivan, W. I. (1989). Proc. R. Ir. Acad. Sect.
B, 89, 105±114.
Burke, A. J. & O'Sullivan, W. I. (1997). Tetrahedron, 53, 8491±8500.
Coppens, P., Leiserowitz, L. & Rabinovich, D. (1965). Acta Cryst. 18, 1035±
1038.
C9ÐC3ÐC10ÐC13
C2ÐC3ÐC10ÐC13
O10ÐC10ÐC13ÐC18
176.25 (11)
7.45 (18)
72.54 (16)
C3ÐC10ÐC13ÐC18
O10ÐC10ÐC13ÐC14
C3ÐC10ÐC13ÐC14
106.79 (14)
108.86 (14)
71.80 (17)
Gripenberg, J. & Juselius, B. (1954). Acta Chem. Scand. 8, 734±737.
Litinas, K. E. & Stampelos, X. N. (1992). J. Chem. Soc. Perkin Trans. 1, 21,
2981±2984.
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381±392.
Sheldrick, G. M. (1990). Acta Cryst. A46, 467±473.
Table 2
Hydrogen-bonding geometry (A, ).
ꢁ
Ê
DÐHÁ Á ÁA
DÐH
HÁ Á ÁA
DÁ Á ÁA
DÐHÁ Á ÁA
C4ÐH4Á Á ÁO2i
0.985 (14)
0.985 (14)
1.016 (18)
1.00 (2)
2.480 (14)
2.582 (13)
2.47 (2)
3.4454 (16)
3.0598 (15)
3.460 (2)
166.6 (10)
109.9 (10)
163.7 (15)
128.0 (12)
È
Sheldrick, G. M. (1997). SHELXL97. University of Gottingen, Germany.
Spek, A. L. (1990). Acta Cryst. A46, C-34.
Spek, A. L. (1991). PLUTON. University of Utrecht, The Netherlands.
Stoe & Cie (1999). IPDS Software. Version 2.92. Stoe & Cie, Darmstadt,
Germany.
C4ÐH4Á Á ÁO10
C11ÐH112Á Á ÁO6ii
C12ÐH123Á Á ÁO2i
2.547 (17)
3.2606 (18)
Symmetry codes: (i) x; y 1; z; (ii) x; 12 ‡ y; 21 z.
Walter, R., Zimmer, H. & Purcell, T. C. (1966). J. Org. Chem. 31, 3854±3857.
ꢀ
486 Anthony J. Burke et al. C17H14O4
Acta Cryst. (2000). C56, 484±486