The use of the triptycene framework for observing O...C=O molecular interactions

Article abstract of DOI:10.1039/c1ce05955f

The triptycene skeleton has been used to measure (1,5) interactions between aldehyde groups, placed at both sp³ centres, and hydroxy or methoxy groups, placed at the respective ortho position on a benzene ring; HO...CHO interactions of 2.621-2.624 A and MeO...CHO interactions of 2.528-2.584 A were observed with the O...C vector making angles of 105.3-133.7° with the carbonyl bond. The lack of a competing conjugation with the framework for the electrophilic group is a favourable factor compared to the use of peri-naphthalene systems. This journal is The Royal Society of Chemistry.

Full text of DOI:10.1039/c1ce05955f

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PAPER
The use of the triptycene framework for observing O/C]O molecular
interactions†
Alberth Lari,a Mateusz B. Pitak,b Simon J. Coles,b Emma Bresco,a Peter Belser,c Andreas Beyeler,c
d
Melanie Pilkington and John D. Wallis
a
*
Received 27th July 2011, Accepted 13th September 2011
DOI: 10.1039/c1ce05955f
The triptycene skeleton has been used to measure (1,5) interactions between aldehyde groups, placed at
both sp3 centres, and hydroxy or methoxy groups, placed at the respective ortho position on a benzene
ꢀ
ꢀ
ring; HO/CHO interactions of 2.621–2.624 A and MeO/CHO interactions of 2.528–2.584 A were
observed with the O/C vector making angles of 105.3–133.7ꢀ with the carbonyl bond. The lack of
a competing conjugation with the framework for the electrophilic group is a favourable factor
compared to the use of peri-naphthalene systems.
Introduction
Peri-disubstituted naphthalenes have been used extensively for
investigating the interactions between pairs of substituents, e.g.
hydrogen bonding in the ‘‘proton sponge’’ cations 11 and
interactions of dimethylamino groups with a wide range of
functionalities including Al, Si and Se centred groups e.g. in
2–4.2 Peri-naphthalene systems have also been used for the
investigation of (1,5) nucleophile/electrophile interactions
between the common functional groups in organic chemistry
e.g. involving –NMe2, –OMe or –SMe as the nucleophile and
carbonyl based groups3 or electron deficient alkenes as the
electrophile, e.g. 5–8.4–6 For the more reactive dimethylamino
group, a significant degree of bond formation with very reac-
tive electrophilic centres to form zwitterionic structures such as
9 has been observed.4,6 Charge density measurements by X-ray
crystallography and topological analysis of the total electron
density are now being used to probe more deeply interactions
that are mediated by the valence electrons. Following this
approach a very detailed study of salts of proton sponges such
as 1 and its free base have been reported by Mallinson and
Wozniak et al.,7 as well as the study of a nucleophile/electro-
phile system.8
aSchool of Science and Technology, Nottingham Trent University, Clifton
Lane, Nottingham, NG11 8NS, UK. E-mail: john.wallis@ntu.ac.uk
bNational Crystallography Service, School of Chemistry, University of
Southampton, Highfield Campus, Southampton, SO17 1BJ, UK
cDepartment of Chemistry, University of Fribourg, Chemin du Museꢁe 9,
CH-1700 Fribourg, Switzerland
Schiemenz has proposed other approaches to estimating the
bond formation between a dimethylamino group and a peri
substituent based on (a) the molecular geometry of the dime-
thylamino group2 and (b) the one bond coupling constant
dDepartment of Chemistry, Brock University, 500 Glenridge Ave, St
Catharines, Ontario, Canada L2S 3A1
1
between 13C and H in the methyl group.9 A greater degree of
pyramidality at the nitrogen atom or an increase in the 13C,1H
† CCDC reference numbers 837139–837143. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/c1ce05955f
coupling constant in the N-methyl group indicate a greater
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degree of bond formation. Akiba has investigated peri interac-
tions in trisubstituted anthracene systems, for example between
two dimethylamino groups and a boron or ester group lying
between them, or between two methoxy groups and a carboca-
tionic centre or an allene derivative containing formally penta- or
hexa-coordinate carbon.10 The 2,20-disubstituted biphenyl
system has also been used to investigate (1,6) molecular inter-
actions where the substituents are no longer constrained to be
near one another.11
Fig. 1 Relative orientation of the aldehyde and flanking hydroxyl
groups in gossypol clathrates.
The success of the peri-naphthalene system for observing such
interactions is dependent on whether the interaction is sufficient to
overcome the tendency of the functional group, especially the
electrophilic one, to conjugate with the naphthalene ring system,
especially when there is no large 1,6 steric interaction between the
electrophilic group with the ortho H atom. Thus, in the molecules
10 and 11 containing a methoxy or methylthio peri group, X-ray
crystallography shows the substituent’s electrophilic alkene bond
makes a torsion angleof only 46.2 or 36.4ꢀ with the aromatic ring’s
carbon–carbon bond to the ortho position.5,12 This is in contrast to
the corresponding cases where a more reactive dimethylamino
group is the nucleophilic centre (5 and 6) and where this angle is
56.5 and 50.5ꢀ.4,6 In naphthalenes 12–14 the peri-interaction with
the aldehyde group is insufficient to overcome the tendency of the
carbonyl group to conjugate with the ring and the C]O/ring
torsion angles are only 11–31ꢀ.13 Another issue is that for
a nucleophile of type –X–H, where X is a heteroatom, hydrogen
bonding between the two peri groups may take place.
electrophilic groups located on the sp3 carbon atoms, so that they
cannot be involved in conjugation, and so therefore fully avail-
able for interaction with electron rich centres at the 1- and
4-positions. As a first step we have investigated the interactions
between hydroxyl or methoxy groups with aldehyde groups in
compounds 19 and 20. Prior to our studies, Oki et al. used the
relative population of rotamers, determined by NMR spec-
trometry, in 1,9-disubstituted triptycene derivatives to investi-
gate 1,6 molecular interactions e.g. between a 1-methoxy or
-chloro group and the carbonyl function of a 9-formylmethyl
group, as well as in models for SN2 reactions involving
a 1-methoxy and a 9-chloromethyl group.14 The triptycene
system has also been used recently by Gung et al. for examining
p–p stacking between aromatic groups15 and interactions
between methoxy or C–H groups and aromatic p systems.16
The deficiency of the peri-naphthalene system as a model
system for observing nucleophile/electrophile interactions
involving hydroxyl groups is illustrated rather well by the crystal
structures of 15 and 16 in which the peri-related hydroxyl and
aldehyde group lie in the naphthalene plane and are splayed
apart, presumably so that a hydrogen bond can form between the
two groups. Although the hydroxyl hydrogen atom was not
unambiguously located in either case, the peri-groups are clearly
splayed apart. Thus, the OH group is splayed out by 4–6ꢀ and the
CHO splayed in the opposite direction by 8–11ꢀ, with (H)O/O
Discussion
ꢀ
(]C)contact distances of 2.51–2.54 A consistent with an internal
Triptycenes 19 and 20
hydrogen bond in 15 and 16 respectively forming a seven-
membered ring.17,18 There is a large family of clathrates from
gossypol 1719 in the Cambridge Structural Database20 which
contain a peri aldehyde group but with both peri and ortho
hydroxyl groups. The ninety observations prefer to show an
internal hydrogen bond from the aldehyde to the ortho hydroxyl
group forming a six-membered ring, which leaves the aldehyde
group in the aromatic plane and with the peri hydroxyl group
oriented so as to direct an sp2 type lone pair towards the aldehyde
hydrogen atom (Fig. 1). The mean HO/H(C]O) distance is
The triptycene systems 19 and 20 which contain two pairs of
potential interactions between hydroxy or methoxy groups and
aldehydes were prepared in several steps from anthracene as
published by two of us earlier.21 The bis(acetal) of anthracene-
9,10-dicarbaldehyde 21 undergoes a Diels–Alder reaction with
benzoquinone to give the sterically crowded adduct 22 which
contain a fragment which is the diketo tautomer of a quinol.
Treatment with acid tautomerises this grouping to the quinol and
also deprotects the two aldehyde groups to yield 1,4-dihydroxy-
triptycene-9,10-dicarbaldehyde 19. Treatment with methyl
iodide converts 19 to the dimethoxy compound 20. Slow evap-
oration of solutions of the 1,4-dihydroxy-triptycene derivative 19
in acetonitrile or ethyl acetate gave two crystalline solvates,
whose structures were determined by X-ray crystallography at
120 K and 150 K respectively. The acetonitrile solvate was well
ordered, but the second solvate contains channels running
through the structure which contain ethyl acetate molecules
which are not well ordered with respect to the rest of the struc-
ture. The molecular structure and crystal packing for 19$CH3CN
are shown in Fig. 2–5, with selected geometry in Table 1. The
ꢀ
2.04 A and suggestive of an attractive interaction.
Thus, we decided to investigate the triptycene ring system 18 as
an alternative scaffold for examining (1,5) interactions, with
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Fig. 2 Two views of the molecular structure of 19 in 19$CH3CN drawn with anisotropic displacement parameters at the 50% level.27,29
ꢂ
crystal system is triclinic and the space group P1. Most notable is
third angle is involved in the O/C]O interaction (113.7 and
114.4ꢀ). The endocyclic angles at this carbon lie in the range
104.17–106.30ꢀ.
the HO/C]O interaction between the functional groups on
both edges of the triptycene system. The hydroxyl groups lie in
the plane of the attached benzene ring with their sp2 lone pair
directed towards the carbonyl group. The O/C separations are
ꢀ
2.621(2) and 2.679(2) A, well within the sum of van der Waals
ꢀ
radii (ca 3.2 A), and the aldehyde groups are oriented so that the
O/C]O angles are 120.07(13) and 124.72(15)ꢀ. The C–OH
bonds are tilted slightly towards their respective carbonyl group
neighbours by 1.6–1.7ꢀ. The plane of each aldehyde group lies
quite close to the plane of one unsubstituted benzene ring so that
there are contacts from the aldehyde O atoms to ortho H atoms
ꢀ
of 2.38 and 2.35 A. The carbonyl bonds make torsions of 15.5
and 18.3ꢀ with the respective bond from the adjacent sp3 C to this
benzene ring. The aldehyde planes lie as 75.7–77.7ꢀ to the other
ꢀ
unsubstituted benzene ring, and there is a contact of 2.48 A from
the ortho H atom to the carbonyl C atom in both cases, with the
H/C vectors lying at 101.8 and 99.3ꢀ to the carbonyl group. The
exocyclic angles at the two sp3 C atoms of the framework are not
symmetrical and are related to the disposition of the carbonyl
group with respect to the two adjacent ortho H atoms. The
largest angle (119.3 and 118.3ꢀ) acts to widen the separation
between the carbonyl O atom and the nearer ortho H atom, and
the smallest angle (both 107.5ꢀ) relates to the deflection of the
plane of the carbonyl group towards the other ortho H atom. The
The molecules are packed in layers with two of the three
benzene rings lying face to face with other benzene rings, and
with pairs of centrosymmetrically related acetonitrile molecules
lying in pockets between the molecules of 19 (Fig. 4) One
carbonyl group is involved in hydrogen bonding to a hydroxyl
group in the next layer with close to linear geometry at the H
ꢀ
atom. The O/O and O/H distances are 2.831(2) and 1.96(3) A,
with an angle at the H atom of 170.4ꢀ and at the carbonyl O atom
of 158.0ꢀ. The second hydroxyl group makes a hydrogen bond to
ꢀ
ꢀ
an acetonitrile molecule (O/N: 2.824(2) A, N/H: 1.91(2) A),
with angles at the H and N atoms of 175.0 and 138.8ꢀ respectively
(Fig. 5). It is interesting to note that the carbonyl group which is
hydrogen bonded makes a shorter intramolecular contact to its
ꢀ
neighbouring hydroxyl group (O]C/OH: 2.621 A) than the
ꢀ
one which is not (by 0.058 A) and has a longer carbonyl double
ꢀ
bond (by 0.022 A), which would be consistent with the polarizing
Fig. 3 Molecular structure of 19 in 19$CH3CN viewed through the
plane of the disubstituted benzene ring, drawn with anisotropic
displacement parameters at the 50% level.27,29
effect of hydrogen bonding on the p electron cloud of the
double bond.
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Nevertheless, it is clear that the conformation of triptycene 19 is
similar to that in the acetonitrile solvate, showing HO/C]O
interactions. In contrast to the acetonitrile solvate, both carbonyl
groups are hydrogen bonded to hydroxyl groups of other
molecules of 19. The molecular structure and crystal packing
arrangement are shown in Fig. 6. The HO/C]O contacts are
ꢀ
2.664(5) and 2.654(4) A, and the O/C O/C vector makes
angles of 126.3(2) and 133.7(3)ꢀ with the carbonyl bond. Each
aldehyde group makes a torsion of 38.5 or 23.3ꢀ with the bond
from the adjacent sp3 carbon atom to the nearest benzene ring,
and the contacts between the carbonyl O atoms and the ortho H
atoms are 2.56 and 2.41 A. A further geometric analysis23,24 of the
ꢀ
packing arrangements exhibited by the two different solvates of
triptycene 19 revealed a one dimensional similarity along [010] as
shown in Fig. 7.
Fig. 4 Crystal packing of 19$CH3CN showing location of solvent
molecules in pockets between the triptycene molecules, drawn in ‘ball and
stick’ mode.27
Crystals of the dimethoxy-triptycene derivative 20 were grown
from DCM. The crystal system is monoclinic and the space
group is Pa with two unique molecules in the asymmetric unit
and thus four crystallographically unique MeO/C]O interac-
tions. The two molecules are illustrated in Fig. 8 and the packing
arrangement is shown in Fig. 9. The overall geometries of the
four interactions are similar, though the influences of other
packing effects leads to some variations. Each of the methoxy
groups lies close or reasonably close to the plane of the attached
aromatic ring, so that it directs an sp2 type lone pair towards the
carbon atom of a carbonyl group at a bridgehead position. The
aldehyde groups are oriented so that the (Me)O/C]O angles lie
in the range 105.24–114.60ꢀ, and each aldehyde group lies close
The crystal structure of the ethyl acetate solvate of triptycene
19 contains channels running through successive layers of
molecules of 19 which contain ethyl acetate that are not ordered
with respect to the rest of the crystal structure. The final structure
reported here is after the application of the PLATON/
SQUEEZE program22 to remove the solvent’s electron density
from the final model. The crystal system is triclinic, and space
ꢂ
group is P1. The accuracy of the structure is lower than that of
the other solvate, and some of the errors in the model are
absorbed into the anisotropic displacement parameters, partic-
ularly the carbonyl O atoms and the unsubstituted benzene rings.
Fig. 5 Hydrogen bonding pattern in crystal structure of 19$CH3CN drawn in ‘ball and stick’ mode.27
Table 1 Geometric details of O/C]O interactions
ꢀ
ꢀ
C]O/A
ꢀ
ꢀ
Compound
19$CH3CN
19$EtOAca
20
O/C(]O)/A
O/C]O Angle/ꢀ
O/H(ortho)/A
Torsion O]C–C(sp3)–C(benzene)
C]O/HO/A
2.621(2)
2.679(2)
2.664(5)
2.654(4)
2.534(9)
2.542(8)
2.584(9)
2.528(9)
120.07(13)
124.72(15)
133.7(3)
126.3(2)
105.3(5)
113.9(5)
114.6(5)
111.5(5)
1.209(2)
1.187(2)
1.089(4)
1.189(3)
1.190(9)
1.197(7)
1.203(8)
1.210(8)
2.38
2.35
2.56
2.41
2.28
2.30
2.36
2.32
15.5(3)
18.3(3)
38.5(6)
23.3(5)
11.9(11)
3.6(10)
7.3(10)
6.9(11)
1.96
—
2.03
2.02
—
—
—
—
a
The disordered solvent was excluded from this structural model using the PLATON/SQUEEZE program.
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Fig. 6 Crystal structure of 19.CH3CO2C2H5 (a) showing a single molecule with anisotropic displacement parameters drawn at the 50% level, (b)
showing the channels running along the a axis between molecules of 19 (drawn in space filling mode) which are filled with ethyl acetate molecules (not
shown).27
Fig. 7 Crystal packing of the two different solvates of 19, showing one dimensional similarity along [010].
Fig. 8 Structures of the two independent molecules of 20 with the anisotropic displacement parameters drawn at the 50% level.27,29
to the plane of another of benzene ring. The O/C separations
shown by the four interacting pairs lie in the range 2.528(9)–2.584
the plane of an unsubstituted benzene ring leads to short (1,6)
O/H contacts between the carbonyl O atom and an ortho
ꢀ
aromatic H atom (2.28–2.36 A). The methoxy groups are dis-
ꢀ
ꢀ
(9) A with an average value of 2.547 A. Full details of the
molecular geometries of the four interactions are given in Table
1. The range of variation between the interaction geometries is
illustrated by the torsion angle between the C–O bond of the
methoxy group and the nearest aromatic C,C bond which varies
from 4.3 to 22.4ꢀ. The orientation of the aldehyde group close to
placed towards the carbonyl groups due to the steric interaction
between the methyl group and an ortho H atom, with the C
(aryl)–OMe bond displaced by 3.7–4.5ꢀ from the symmetrical
position. The two independent molecules of 20 pack in separate
layers perpendicular to the c axis.
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which are somewhat mitigated by the pair of particularly long
C–C bonds. The quinone ring is flexed to move the keto O atoms
away from the dioxolane substituents, and the keto O atoms lie
ꢀ
1.367 and 0.685 A out of the plane of the four non-carbonyl
carbon atoms of the ring. The considerable difference in these
values is related to the quite different interactions they make with
their adjacent dioxolane rings. In the former case, the interaction
between carbonyl and dioxolane groups involves an acetal O
atom making a short contact with the carbonyl carbon of the
ꢀ
ketone (2.669 A) which may be attractive in nature, while in the
other case, the shortest contact in the interaction is a 1,6 contact
between the carbonyl O atom and the methine H atom of the
ꢀ
dioxolane ring (2.35 A). In this way too, repulsive interactions
between keto and dioxolane oxygen atoms are minimized by
ꢀ
keeping them more than 3 A apart.
Conclusion
The triptycene skeleton has been demonstrated to be a useful
scaffold for investigating (1,5) interactions between functional
groups. A particular advantage is that the group located on the
central sp3 carbon atom cannot conjugate with the framework as
happens in some peri-naphthalene systems. The use of the trip-
tycene skeleton has the potential for extension further towards
systems where partial bond formation may take place, depending
on the reactivities of the groups chosen and on the installation of
ortho substituents to create increased steric pressure. Further
work in this direction is underway.
Fig. 9 Crystal packing arrangement of 20 showing packing of the two
independent molecules of 20 (blue and green) in layers perpendicular to
the c axis.
Diels–Alder adduct 22
The Diels Alder adduct 22 between benzoquinone and the
anthracene bis(acetal) 21 is a particularly interesting molecule,
since firstly solution NMR suggests it is a tautomer of a quinol
derivative and secondly there are likely to be interactions
between the adjacent carbonyl and acetal groups. Hence the
crystal structure was determined by X-ray diffraction at 100 K.
The molecular structure is shown in Fig. 10. The molecule is most
notable for the lengths of the two C–C bonds which are formed
Experimental
X-Ray crystallographic measurements were made on Nonius
KappaCCD area-detector diffractometer located at the window
of a Nonius FR591 rotating-anode X-ray generator, equipped
ꢀ
with a molybdenum target (lMo-Ka ¼ 0.71073 A). (for 19.aceto-
nitrile and 20) or a Bruker KAPPA APEX II CCD diffractom-
eter equipped with an Oxford Cryosystems low temperature
device (for 19.ethyl acetate and 22). Structures were solved and
refined with the SHELXS and SHELXL suites25 using the
XSEED26 interface.
on addition of the benzoquinone to the anthracene: 1.5841(19)
3
ꢀ
ꢀ
and 1.5894(19) A, ca 0.04–0.05 A longer than the standard sp C–
sp3C bond. Furthermore, the bond joining these two bonds,
which had played the part of the dienophile in the Diels Alder
ꢀ
reaction, is also strained and is 1.5597(19) A long. The two
Crystal data for 19.CH3CN: C22H14O4.C2H3N, Mr ¼ 383.39,
ꢂ
ꢀ
dioxolane rings adopt envelope conformations with an O atom at
the flap, but adopt different staggered conformations with
respect to the rest of the molecule, with either a C–O bond or
a C–H bond lying anti to the quinone grouping. There are steric
interactions between the pairs of carbonyl and dioxolane groups,
triclinic, P1, a ¼ 9.0118(3), b ¼ 9.6549(4), c ¼ 11.6967(5) A, a ¼
ꢀ
3
ꢀ
80.718(3), b ¼ 87.782(3), g ¼ 65.542(2) , V ¼ 913.81(6) A , Z ¼
2, Dcalc. ¼ 1.39 g cmꢁ3, T ¼ 120 K, m ¼ 0.095 mmꢁ1, F(000) ¼ 400,
4190 unique reflections (Rint ¼ 0.0588), 2991 with I > 2s(I), max.
(sin q)/l ¼ 0.65 Aꢁ1, final R1 ¼ 0.055, wR2 ¼ 0.13.
ꢀ
Fig. 10 Molecular structure of 22 showing the distorted dihydroquinone ring (left) and the two short contacts (O/C]O and C]O/H–C) between
a ketal group and a carbonyl of the dihydroquinone (right).27,29
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K. L. McCormack and D. S. Yufit, J. Am. Chem. Soc., 1999, 121,
ꢁ
Crystal data for 19.0.75CH3CO2C2H5: C22H14O4$0.75-
ꢂ
4640–4646; P. R. Mallinson, K. Wozniak, G. T. Smith and
K. L. McCorkmack, J. Am. Chem. Soc., 1997, 119, 11502–
11509.
C4H8O2, Mr ¼ 408.4, triclinic, P1, a ¼ 9.3754(7), b ¼ 9.6285(7),
ꢀ
ꢀ
c ¼ 11.4470(9) A, a ¼ 69.585(4), b ¼ 69.800(4), g ¼ 77.586(4) ,
V ¼ 903.60(12) A , Z ¼ 2, Dcalc. ¼ 1.50 g cmꢁ3, T ¼ 150 K,
3
ꢀ
8 K. A. Lyssenko, S. M. Aldoshin and M. Y. Antipin, Mendeleev
Commun., 2004, 14, 98–100.
€
9 G. P. Scheimenz, S. Petersen and S. Porkson, Z. Naturforsch., 2003,
58b, 715–724.
m ¼ 0.106 mmꢁ1, F(000) ¼ 428, 4462 unique reflections
ꢁ1
ꢀ
(Rint ¼ 0.0455), 2208 with I > 2s(I), max. (sin q)/l ¼ 0.67 A
,
final R1 ¼ 0.070, wR2 ¼ 0.18. The final structure refinements were
done after application of the PLATON/SQUEEZE program to
exclude the channels of ethyl acetate from the model.
10 T. Yamaguchi, Y. Yamamoto, D. Kinoshita, K. Akiba, Y. Zhang,
C. A. Reed, D. Hashizume and F. Iwasaki, J. Am. Chem. Soc.,
2008, 130, 6894–6895; M. Yamashita, Y. Yamamoto, K. Akiba,
D. Hashizume, F. Iwasaki, N. Takagi and S. Nagase, J. Am. Chem.
Soc., 2005, 127, 4354–4371; K. Akiba, M. Yamashita,
Y. Yamamoto and S. Nagase, J. Am. Chem. Soc., 1999, 121,
10644–10645.
11 J. O’Leary and J. D. Wallis, Org. Biomol. Chem., 2009, 7, 225–228.
12 J. O’Leary, P. C. Bell, J. D. Wallis and W. B. Schweizer, J. Chem.
Soc., Perkin Trans. 2, 2001, 133–139.
13 J. C. Gallucci, D. J. Hart and D. G. J. Young, Acta Crystallogr., Sect.
B: Struct. Sci., 1998, 54, 73–81.
14 M. Oki, Acc. Chem. Res., 1990, 23, 351; M. Oki, G. Izumi,
G. Yamamoto and N. Nakamura, Bull. Chem. Soc. Jpn., 1982, 55,
159–166.
15 B. W. Gung, B. U. Emenike, C. N. Alverez, J. Rakovan,
K. Kirschbaum and N. Jain, Tetrahedron Lett., 2010, 51, 1648–
1650; B. W. Gung, F. Wekesa and C. L. Barnes, J. Org. Chem.,
2008, 73, 1803–1808; B. W. Gung, X. Xue and Y. Zou, J. Org.
Chem., 2007, 72, 2469–2475.
16 B. W. Gung, B. U. Emenike, M. Lewis and K. Kirschbaum, Chem.–
Eur. J., 2010, 16, 12357–12362; B. W. Gung, Y. Zou, Z. Xu,
J. C. Amicangelo, D. G. Irwin, S. Ma and H.-C. Zhou, J. Org.
Chem., 2008, 73, 689–693.
Crystal data for 20. C24H18O4, Mr ¼ 370.38, monoclinic, Pa,
ꢀ
ꢀ
a ¼ 14.0278(3), b ¼ 7.9798(2), c ¼ 15.6964(4) A, b ¼ 96.197(2) ,
V ¼ 1746.77(7) A , Z ¼ 4, Dcalc. ¼ 1.41 g cmꢁ3, T ¼ 120 K, m ¼
3
ꢀ
0.096 mmꢁ1, F(000) ¼ 776, 3991 unique reflections, 2985 with I >
2s(I), max. (sin q)/l ¼ 0.65 Aꢁ1, final R1 ¼ 0.062, wR2 ¼ 0.013.
ꢀ
The crystal was refined as a nonmerohedral twin with two
component ratio 0.52 : 0.48.
Crystal data for 22. C26H22O6, Mr ¼ 430.44, monoclinic,
ꢀ
C2/c, a ¼ 21.837(2), b ¼ 9.297(1), c ¼ 19.231(2) A, b ¼ 100.008
(3) , V ¼ 3845.0(7) A , Z ¼ 8, Dcalc. ¼ 1.49 g cmꢁ3, T ¼ 100 K,
ꢀ
3
ꢀ
m ¼ 0.106 mmꢁ1, F(000) ¼ 1808, 4773 unique reflections
ꢁ1
ꢀ
(Rint ¼ 0.0335), 3746 with I > 2s(I), max. (sin q)/l ¼ 0.67 A
,
final R1 ¼ 0.043, wR2 ¼ 0.11.
Acknowledgements
We thank the EPSRC for grant (EP/E018203/1) from the Phys-
ical Organic Chemistry Initiative and for funding the National
Crystallography Service, the EPSRC mass spectrometry service
for spectra, and the Chemical Database Service28 for access to the
Cambridge Structural Database. M. Pilkington thanks (NSERC,
Discovery Grant) the CFI (New Opportunities Fund) and the
CRC (Tier II Research Chair).
17 Crystal data for 18: C11H8O2, Mr ¼ 172.17, monoclinic, P21/c, a ¼
ꢀ
ꢀ
7.1576(5), b ¼ 29.301(3), c ¼ 7.6537(7) A, b ¼ 91.699(4) , V ¼
3
1604.5(2) A , Z ¼ 8, Dc ¼ 1.43 g cmꢁ3, T ¼ 120 K, m ¼ 0.098
ꢀ
mmꢁ1, F(000) ¼ 720, 2813 unique reflections (Rint ¼ 0.0580), 2442
with I > 2s(I), max. (sin q)/l ¼ 0.59 Aꢁ1, final R1 ¼ 0.095, wR2 ¼ 0.23.
ꢀ
18 J.-P. Buisson, J. Kotzyba, J.-P. Lievremont, P. Demerseman,
N. Platzer, J.-P. Bideau and M. Cotrait, J. Heterocycl. Chem., 1993,
30, 739.
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1994, 3, 147–65.
20 F. H. Allen, Acta Crystallogr., Sect. B: Struct. Sci., 2002, 58, 380–388.
21 A. Beyeler and P. Belser, Coord. Chem. Rev., 2002, 230, 29–39.
22 A. L. Spek (2005) PLATON, A Multipurpose Crystallographic Tool,
Utrecht University, Utrecht, The Netherlands.
23 T. Gelbrich and M. B. Hursthouse, CrystEngComm, 2005, 7, 324–336.
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25 G. M. Sheldrick, Acta Crystallogr., Sect. A: Found. Crystallogr., 2007,
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This journal is ª The Royal Society of Chemistry 2011