Novel C3-symmetric molecular scaffolds with potential facial differentiation

Article abstract of DOI:10.1002/1521-3765(20020517)8:10<2274::AID-CHEM2274>3.0.CO;2-T

The conversion of 1,3,5-substituted benzene and mesitylene by electrophilic aromatic substitution and Sonogashira cross-coupling, respectively, furnished the C₃-symmetric, hexasubstituted benzene derivatives 1 and 2 with an alternating substitu

Full text of DOI:10.1002/1521-3765(20020517)8:10<2274::AID-CHEM2274>3.0.CO;2-T

FULL PAPER
Novel C3-Symmetric Molecular Scaffolds with Potential Facial Differentiation
Gunther Hennrich, Vincent M. Lynch, and Eric V. Anslyn*[a]
Abstract: The conversion of 1,3,5-sub-
stituted benzene and mesitylene by
electrophilic aromatic substitution and
Sonogashira cross-coupling, respective-
ly, furnished the C3-symmetric, hexasub-
stituted benzene derivatives 1 and 2 with
an alternating substitution pattern.
Based on the molecular scaffolds ob-
tained, the two systems serve as model
compounds for novel receptor mole-
cules with distinct geometric features.
X-ray structures have been obtained for
1 and 2, which are discussed in regard to
their aptitude as receptor platforms or
supramolecular building blocks. By
looking at the rotational barriers for
the functional groups placed around the
molecular scaffolds by variable temper-
ature 1H NMR spectroscopy, 1 and 2
turn out to exist in rapidly interconvert-
ing conformations. The alignment of
these potential binding groups around
the molecular scaffolds should be
strongly biased by specific interactions
with suitable guest molecules.
Keywords: cross-coupling
design molecular recognition
supramolecular
¥ ligand
¥
¥
receptors
chemistry
¥
blocks in supramolecular assemblies.[7] Yet, when targeting
guest molecules or aiming at structurally matching partners,
their size is restricted by the phenyl platform.
We report here new molecular scaffolds that allow the
introduction of altered function on either face. The variation
of the geometry of the functional groups on the different faces
of the benzene core, or the extension of the benzene platform
to larger sizes, could lead to molecular receptors that target a
whole variety of new potential guest molecules.
Introduction
During the last few years, an emerging number of supra-
molecular systems has been reported in which the principle of
steric gearing is employed to circumvent the difficulties in
synthesis arising form covalent architecture.[1, 2] Here, the
suitable preorganization of functional groups and conforma-
tional constraint is achieved by controlling the stereochem-
istry through steric hindrance of the substituents around a
rigid platform.[3]
In this context, persubstituted benzenes have been intense-
ly investigated,[4] mainly due to their applications in supra-
molecular chemistry.[5] However, all of the benzene based
conformationally controlled systems are either symmetrically
hexasubstituted with the same six functional groups (A); or in
the case of 1,3,5-triethyl benzene derivatives (B), facial
segregation is brought about through different functionalities
in the 2,4, and 6-positions, while the triethyl-face lacks any
function.[6] Nevertheless, both compound classes have found
wide application in molecular recognition, and as building
Results and Discussion
In this paper, we present two representatives of alternating
hexasubstituted benzene scaffolds: 1,3,5-tris(acetoxymethyl)-
2,4,6-thiophenyl benzene (1) and 1,3,5-tris(acetoxymethyl)-
2,4,6-tris(2-ethoxycarbonylphenyl)ethynyl benzene (2). The
platforms are expected to exist in rapidly interconverting
conformations, and are drawn as facially differentiated (see
below).
R
R
R
R X
X
R
OAc
R
R
X
X
OAc
R
AcO
S
EtO2C
AcO
X
OAc
OAc
S
R
S
X = S or -CH2
EtO2C
B
A
CO2Et
1
2
[a] Prof. E. V. Anslyn, Dr. G. Hennrich, Dr. V. M. Lynch
Department of Chemistry and Biochemistry
Syntheses: The syntheses of both target molecules is con-
ducted in a modular approach. Aryl and acetyl moieties are
chosen as representative functionalities that could be easily
The University of Texas at Austin, Austin, TX 78712-1167 (USA)
Fax : (‡1) 512-471-7791
E-mail: anslyn@ccwf.cc.utexas.edu
2274
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Chem. Eur. J. 2002, 8, No. 10

2274 2278
Table 1. Reaction conditions for Sonogashira coupling of acetylene
2-iodoethoxybenzoic acid.[16]
9 with
replaced in the synthesis by other similar reactants. By
following the pathway depicted in Scheme 1, these
functionalities are introduced in the last two steps for
both 1 and 2 (Scheme 1). The starting materials 5 and 9
are easily accessible and can be prepared on a large
scale. The synthesis of 5 starting from tris-bromomesi-
tylene is straightforward.[8] Bromination of 1,3,5-tris-
bromomesitylene (3) with elemental bromine gives
compound 4. The threefold substitution of bromine
with potassium acetate yields the tris-acetate 5 as a versatile
starting material. As shown by Lehn et al., the final
nucleophilc substitition by sodium thiophenolate proceeds
smoothly under mild conditions by using DMI as solvent.[9]
Working in DMF requires harsher conditions and lowers the
yield considerably.[10]
Run Catalyst (mol%)
Base/solvent T [8C] t [h] Yield[a] [%] Ref.
[13]
[14]
[15]
A
B
C
[Pd(PPh3)2Cl2] (4), CuI (8) DIEA[b]/THF RT
36
72
48
8
15
23
[Pd(PPh3)2Cl2] (5), CuI (5) NEt3
[Pd(PPh3)4] (5), CuI (5) piperidine
RT
RT
[a] Isolated yields, in case of run C calculated on the isolated deacylated tris-alcohol
compound (2a). [b] DIEA: diisopropylamine.
Stuctural investigations: As seen by X-ray crystallography, the
thiophenyl rings of 1 are positioned above or below the
central phenyl plane. The phenyl substituents are oriented
nearly aligned with the S to central benzene bond, instead of
being perpendicular to it. The C(Ar)-S-C(Ar) angles are in
the range of 103 1048 (Figure 1). As a consequence of this,
two molecules of 1 form a dimer, interlocking with two
thiophenyl groups each (Figure 1b). The two free thiophenyl
moieties place each dimer into a packing superstructure. This
packing creates the two-up-one-down configuration of the
acetoxymethyl and the thiophenyl groups in the solid state.[17]
Molecule 2 is almost planar with the acetoxylmethyl groups
pointing perpendicular out of the plane. The two-up-one-
down conformation of these substituents is attributed to the
crystal packing. The expected unbiased conformational pref-
erence of the aryl groups around the triple bonds in solution is
reflected in the positioning of the ethoxycarbonyl functions
towards or away from each other in the solid state (Figure 2a).
The distance between the three arylcarbonyl functions,
analogous for potential binding sites, is approximately 7 ä
The preparation of compound 2 is based on the coupling of
aryl iodides with free acetylenes under Sonogashira condi-
tions.[11] NBS bromination of 7, whose synthesis has been
described,[12] gives the tris-bromide 7 in reasonable yields.
Upon applying a six fold excess of potassium acetate to
substitute the methylene bromides in 8, the acetylene
functions are desilylated at the same time to give 9. Consid-
ering the plethora of various literature procedures with
sometimes subtle differences in the conditions, the choice of
these is crucial in the final coupling reaction of 9 with 2-iodo
ethoxybenzoic acid (Table 1). Finally, owing to the electronic
deactivation of the aryliodide and the steric hindrance of both
the iodide and the alkyne, a 23% yield can be considered
satisfactory for a threefold conversion reaction.
Route (I)
Br
OAc
S
OAc
Br
AcO
S
Br
Br
Br
Br
OAc
Br
AcO
Br2, DBE
KOAc, HOAc
NaSPh
S
Br
refl., 24 h
92%
DMI, 24 h
r.t., 72%
140oC, 24 h
90%
Br
Br Br
Br OAc
3
4
5
1
Route (II)
Br
TMS
TMS
TMS
TMS
I
I
TMS-acetylene, NEt3
NBS, DBP
Br
[Pd(PPh3)2Cl2], CuI
r.t., 72 h, 79%
CCl4, refl., 16 h
64%
Br
I
TMS
TMS
6
7
8
OAc
OAc
OAc
2-iodoethoxy-
benzoic acid
EtO2C
AcO
KOAc, DMF
a)
AcO
r.t., 16 h
89%
EtO2C
OAc
CO2Et
9
2
Scheme 1. Syntheses of tris(thiophenyl) compound 1 (route I) and tris(arylacetylene) compound 2 (route II). a) See Table 1 for reaction conditions. DBE:
1,2-dibromoethane; DMI: 1,3-dimethyl-2-imidazolidone; DBP: dibenzoylperoxide.
Chem. Eur. J. 2002, 8, No. 10
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2275

E. V. Anslyn et al.
FULL PAPER
are placed statistically above or below the central benzene
core and are freely rotating. Even at À708C, no rotational
barriers for these substituents can be determined as evidenced
1
by no broadening of the H NMR signals. Similarly, a rapid
rotation of the ethoxycarbonylbenzene moieties around the
acetylenic bonds is observed at this temperature. In support,
calculations have shown for different tolane systems, that the
energetic barrier for the rotation of the phenyl groups around
the acetylene bond is in the order of 0.3 kcalmolÀ1.[19]
In the presence of suitable guest structures, we expect the
substituents to adopt a three-up-three-down conformation of
the binding groups around the benzene plane of 1 and around
the triple-bond expanded platform of 2.
Conclusion
Versatile synthetic routes for two novel molecular scaffolds
have been worked out that allow the introduction of various
functionalities onto a central core. Considering the low
rotational barriers of the ™masked∫ binding substituents
around the core structure, the directing input of a suitable
guest should easily align the functional groups and therefore
induce and bias a two-face preorganisation of the scaffold. For
both 1 and 2, a selective face-dependent interaction is
envisioned by the use of different binding groups as well as
the matching with the different geometries of both faces.
Figure 1. a) Top view of 1. Displacement ellipsoids are scaled to the 30%
probability level. The hydrogen atoms are omitted for clarity. b) Molecules
of 1 form tightly packed dimers around crystallographic inversion centers
at 0, 0, 1³2.
Experimental Section
General methods: All reagents and solvents, which were of the highest
purity available, were obtained from Aldrich. Column chromatography was
carried out with silica gel 60 (No. 7731, Merck). For characterization of the
substances, NMR data were recorded at 258C on a Bruker AC-250
spectrometer, CDCl3 was used as solvent with chemical shifts reported as
ppm and CDCl3 serving as solvent internal standard. Low and high
resolution mass spectra were measured on a Finnigan TSQ70 and a VG
analytical ZAB2-E mass spectrometer, respectively. The variable temper-
ature 1H NMR experiments were carried out on a Bruker AMX-500
spectrometer. The temperature was varied in 208C increments from À708C
to 908C in [D8]toluene as solvent for 1 and 2, and additionally for 1 from 20
to 1008C in [D6]DMSO.
Materials
1,3,5-Tris(bromo)-2,4,6-tris(bromomethyl) benzene (4): Bromine (9.8 g,
3.14 mL, 0.06 mol) was added over a period of 1 h to a refluxing solution of
1,3,5-tris-bromomesitylene (3, 10 g, 0.012 mol) in 1,2-dibromoethane
(40 mL) and the reaction mixture was refluxed for another 24 h. The solid
precipitating from the cold solution was filtered, washed several times with
water and recrystallized from ethanol/benzene (2:1) to give pure 4 as
colorless crystals (4.85 g, 68%). M.p. 2188C; 1H NMR: d ˆ 4.90 (s, 6H;
Figure 2. a) Top view of 2. Displacement ellipsoids are scaled to the 30%
probability level. The hydrogen atoms are omitted for clarity. b) Side view
of 2. The arrow indicates the distance between two arylcarboxy functions.
‡
CH2); 13C NMR: d ˆ 137.40, 128.47 (Ar), 35.50 (Ar-CH2); CI -MS: m/z
‡
(%): 594 (3) [M] , 513 (100), 435(5); HRMS: calcd for C9H6Br6: 587.5569;
found: 587.5559.
while the acetoxy functions encircle a binding site of the same
dimension as in similar systems.[6] Hence, the two-faced
platform contains a wider upper and a narrower lower
™rim∫ poised to distinguish between guests with not only
different functionalities but also of different sizes (Fig-
ure 2b).[18]
As revealed by variable temperature 1H NMR experiments
(in [D8]toluene and [D6]DMSO, respectively), for both
molecules 1 and 2 the respective acetyl or thiophenyl groups
1,3,5-Tris(acetoxymethyl)-2,4,6-tris(bromomethyl) benzene (5): Com-
pound 4 (2.0 g, 3.4 mmol) and potassium acetate (2.2 g, 0.022 mol) in
glacial acetic acid (40 mL) were heated for 16 h at 1408C in a sealed tube.
The solvent was removed and the remaining solid was stirred with water
(50 mL) and dichloromethane (50 mL) for 15 min. The phases were
separated. The organic phase was washed subsequently with saturated
bicarbonate solution, water, and brine (50 mL each). After drying over
Na2SO4, the solvent was removed in vacuo and the remaining solid was
recrystallized from ethanol to give pure 5 as colorless crystals (1.62 g,
90%). M.p. 1548C; 1H NMR: d ˆ 5.52 (s, 6H; CH2), 2.08 (s, 9H; CH3);
2276
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Chem. Eur. J. 2002, 8, No. 10

Molecular Scaffolds
2274 2278
13
ˆ
C NMR: d ˆ 170.43 (C O), 135.63, 131.44 (Ar), 68.09 (Ar-CH2), 20.60
and finally by recrystallisation from methanol to give pure 2a as bright
yellow crystals (102 mg, 23%). M.p. 96 988C; 1H NMR: d ˆ 7.91 7.88 (m,
3H; Ar), 7.51 7.10 (m, 9H; Ar), 4.61 (s, 6H; CH2), 4.31 (q, J ˆ 7 Hz, 6H;
CH2CH3), 1.7 (brs, 3H; OH), 1.32 (t, J ˆ 7 Hz; 9H, CH2-CH3); 13C NMR:
‡
‡
(CH3); CI -MS: m/z (%): 533 (3) [M ‡ H] , 471 (100), 445 (64), 417 (19),
393 (14), 365 (3); HRMS: calcd for C15H16O6Br3: 528.8497; found: 528.8480.
1,3,5-Tris(acetoxymethyl)-2,4,6-thiophenyl benzene (1): Compound
5
ˆ
d ˆ 167.61 (CH3CH2-C O), 147.37, 138.40, 134.84, 134.49, 132.10, 130.62,
(500 mg, 0.94 mmol mmol) and sodium thiophenolate (621 mg, 4.7 mmol)
were stirred in DMI (5 mL) under argon at room temperature for 24 h. The
solvent was removed by Kugelrohr distillation. To the remaining solid
water (20 mL) was added, and the suspension was extracted with dichloro-
methane (3 Â 10 mL). The organic phase was dried (MgSO4). The solvent
was removed in vacuo and the remaining solid was recrystallized from
cyclohexane to give pure 1 as colorless crystals (418 mg, 72%). M.p. 136
ꢀ
130.00, 129.51, 127.56, 126.58 (Ar), 115.46, 110.95 (Ar-C C), 61.04 (Ar-
‡
‡
CH2), 31.91 (CH2CH3), 14.23 (CH3CH2); CI -MS: m/z (%): 810 (8) [M] ,
795 (7), 751 (100), 737 (5), 723 (5), 709 (32), 693 (5); HRMS: calcd for
C48H42O12: 810.2676; found: 810.2687.
CCDC-175643 (1) and -175644 (2) contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of charge via
www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge Crys-
tallographic Data Centre, 12 Union Road, Cambridge CB21EZ, UK; (fax:
(‡44)1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk).
1
1388C; H NMR: d ˆ 7.21 6.90 (m, 15H; Ar), 5.65 (s, 6H; CH2), 1.52 (s,
13
ˆ
9H; CH3); C NMR: d ˆ 170.14 (C O), 148.23, 139.46, 137.29, 128.97,
‡
126.93, 125.45 (Ar), 65.29 (Ar-CH2), 20.07 (CH3); CI -MS: m/z (%): 618
‡
(23) [M] , 559 (100), 529 (9), 499 (6), 439 (14); HRMS: calcd for
C33H30O6S3: 618.1205; found: 618.1209.
Acknowledgements
1,3,5-Tris(bromomethyl)-2,4,6-tris(trimethylsilylethynyl) benzene (8):
1,3,5-Tris(trimethylsilylethynyl) mesitylene (7, 2.0 g, 4.9 mmol), N-bromo-
succinimide (0.026 mmol, 4.6 g) and dibenzoyl peroxide (200 mg,
0.8 mmol) were heated in CCl4 (40 mL) at reflux for 16 h. The solution
was cooled, filtered, and the filtrate was concentrated in vacuo. The
remaining yellow oil was purified by column chromatography (hexanes/
benzene 10:1, Rf ˆ 0.60) and the resulting solid was recrystallized from
methanol/ethanol (1:1) to give pure 8 as colorless needles (2.05 g, 64%).
The authors gratefully acknowledge Prof. Yves Rubin for helpful
discussion on the synthetic pathway involving compounds 3 5 and the
financial support by the Beckman Foundation and the National Science
Foundation.
M.p. 184 1888C; 1H NMR: d ˆ 4.82 (s, 6H; CH2), 0.31 (s, 27H; CH3);
[1] J.-M. Lehn, Supramolecular Chemistry: Concepts and Perspectives,
VCH, Weinheim, 1995; for a recent review on synthetic receptors see:
J. H. Hartley, T. D. James, C. J. Ward, J. Chem. Soc. Perkin Trans. 1
2000, 3155 3184; for hydrogen-bonding systems used in noncovalent
synthesis see: L. J. Prins, D. N. Reinhoudt, P. Timmermann, Angew.
Chem. 2001, 113, 2446 2492; Angew. Chem. Int. Ed. 2001, 40, 2382
2426.
[2] D. Makeiff, J. C. Sherman, in Templated Organic Synthesis (Eds.: F.
Diederich, P. J. Stang), Wiley-VCH, Weinheim, 2000.
[3] For the concept of steric gearing in supramolecular chemistry and
selected examples see: G. Hennrich, E. V. Anslyn, Chem. Eur. J. 2002,
8, 2218 2224.
13
ꢀ
‡
C NMR: d ˆ 141.99, 124.10 (Ar), 108.78, 98.04 (C C), 30.08 (Ar-CH2),
‡
À0.47 (CH3); CI -MS: m/z (%): 647 (26) [M ‡ H] , 631 (48), 573 (20), 565
(100), 521 (14), 493 (36); HRMS: calcd for C24H34Si3Br3: 642.9518; found:
642.9507.
1,3,5-Tris(acetoxymethyl)-2,4,6-tris(ethynyl) benzene (9): Compound
8
(500 mg, 0.78 mmol) and potassium acetate (495 mg, 5.0 mmol) were
stirred in dry DMF (5 mL) at room temperature for 16 h. The solvent was
removed. To the remaining solid, water (20 mL) was added, and the
suspension was extracted with dichloromethane (3 Â 10 mL). The organic
phase was dried (MgSO4), the solvent was removed in vacuo, and the
remaining solid was recrystallized from cyclohexane to give pure 9 as
1
[4] D. D. MacNicol, G. A. Downing in Compehensive Supramolecular
Chemistry, Vol. 6 (Eds.: J. L. Atwood, J. E. D. Davies, D. D. MacNicol,
F. Vˆgtle, J.-M. Lehn), Elsevier, Oxford, 1996.
colorless crystals (254 mg, 72%). M.p. 157 1608C; H NMR: d ˆ 5.42 (s,
6H; CH2), 3.56 (s, 3H; C CH), 2.04 (s, 9H; CH3); 13C NMR: d ˆ 170.58
ꢀ
ˆ
ꢀ
ꢀ
(C O), 140.77, 125.86 (Ar), 87.87 (Ar-C C-), 77.14 (C CH), 63.23 (Ar-
‡
‡
[5] P. Prinz, A. Lansky, T. Haumann, R. Boese, M. Noltemeyer, B.
Knieriem, A. de Mejere, Angew. Chem. 1997, 109, 1343 1346; Angew.
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Wagner, D. Astruc, Angew. Chem. 1996, 108, 1842 1845; Angew.
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Cisarova, P. Holy, J. Podlaha, M. Slouf, J. Zavada, Collect. Czech.
Chem. Commun. 2000, 65, 673 694; G. Hennrich, V. M. Lynch, E. V.
Anslyn, Chem. Commun. 2001, 2436 2437.
CH2), 20.44 (CH3); CI -MS: m/z (%): 366 (2) [M] , 343 (2), 307 (100), 265
(8); HRMS: calcd for C21H18O6: 366.1103; found: 366.1099.
1,3,5-Tris(acetoxymethyl)-2,4,6-tris(2-ethoxycarbonylphenyl)ethynyl ben-
zene (2): 2-Iodoethoxybenzoic acid (497 mg, 1.8 mmol) was stirred together
with palladium(ii)-bis(triphenylphosphine)dichloride (51 mg, 0.072 mmol)
and copper(i) iodide (15 mg, 0.072 mmol) in dry degassed triethyl amine
(5 mL) under argon for 30 min, before 9 (175 mg, 0.48 mmol) was added.
The suspension was stirred at room temperature for 72 h. After removing
the solvent, an ammonium hydroxide solution (1n, 25 mL) was added to
the solid residue and the mixture was extracted with ethyl acetate (3 Â
10 mL). The organic phase was dried (MgSO4) and the solvent was
removed in vacuo. The remaining solid was purified by column chroma-
tography (hexanes/ethyl acetate 1:1, Rf ˆ 0.27) and finally by recrystallisa-
tion from cyclohexane/benzene (2:1) to give pure 2 as orange crystals
(58 mg, 15%). M.p. 1548C; 1H NMR: d ˆ 7.98 7.95 (m, 3H; Ar), 7.67 7.64
(m, 3H; Ar), 7.54 7.36 (m, 6H; Ar), 5.75 (s, 6H; CH2), 4.38 (q, J ˆ 7 Hz,
[6] S. L. Wiskur, H. AÔt-Haddou, J. J. Lavigne, E. V. Anslyn, Acc. Chem.
Res. 2001, 34, 963 972.
[7] M. Mayor, J.-M. Lehn, K. M. Fromm, D. Fenske, Angew. Chem. 1997,
109, 2468 2471; Angew. Chem. Int. Ed. 1997, 36, 2370 2372; B. F.
Hoskins, R. Robson, D. A. Szylis, Angew. Chem. 1997, 109, 2861
2863; Angew. Chem. Int. Ed. 1997, 36, 2752 2755; H. A. M. Biemans,
A. E. Rowan, A. Verhoeven, P. Vanoppen, L. Latterini, J. Foekema,
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6H; CH2CH3), 2.05 (s, 9H; CO-CH3), 1.36 (t, J ˆ 7 Hz, 9H; CH2-CH3);
13
ˆ
ˆ
C NMR: d ˆ 170.97 (CH3-C O), 165.37 (CH3CH2-C O), 139.42, 134.40,
ꢀ
131.99, 131.78, 130.24, 128.56, 127.44, 122.93 (Ar), 97.82, 88.44 (Ar-C C),
64.02 (Ar-CH2), 61.21 (CH2CH3) 20.92 (CO-CH3), 14.26 (CH3CH2); CI -
MS: m/z (%): 685 (15) [M] , 524 (16), 519 (14), 515 (14), 447 (76), 335 (69),
‡
‡
[10] A. Van Bierbeeck, M. Gingras, Tetrahedron Lett. 1998, 39, 6283
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305 (20), 299 (10), 263 (100), 253 (22), 185 (43); HRMS: calcd for C42H37O9:
685.2438; found: 685.2446.
1,3,5-Tris(hydroxymethyl)-2,4,6-tris(2-ethoxycarbonylphenyl)ethynyl ben-
zene (2a): 2-Iodoethoxybenzoic acid (552 mg, 2.0 mmol) was stirred
together with palladium(ii)-tetrakis-(triphenylphosphine) (116 mg,
0.1 mmol) and copper(i) iodide (19 mg, 0.1 mmol) in dry degassed
piperidine (3 mL) under argon for 30 min, before 9 (245 mg, 0.67 mmol)
was added. The suspension was stirred at 808C for 48 h. The solvent was
removed and the remaining solid was purified by column chromatography
(hexanes/ethyl acetate 5:1, then 1:1); Rf ˆ 0.42 (hexanes/ethyl acetate 5:2)
[11] K. Sonogashira in Comprehensive Organic Synthesis, Vol. 3 (Eds.:
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Chem. Eur. J. 2002, 8, No. 10
¹ WILEY-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002
0947-6539/02/0810-2277 $ 20.00+.50/0
2277

E. V. Anslyn et al.
FULL PAPER
[15] I. G. Stara, I. Stary, A. Kollarovic, F. Teply, D. Saman, P. Fiedler,
Collect. Czech. Chem. Commun. 1999, 64, 649 672.
(No. 14), Z ˆ 4 in a cell of dimensions: a ˆ 19.6827(4), b ˆ 8.9314(2),
c ˆ 23.8162(5) ä,
b ˆ 99.020(1)8,
Vˆ 4134.97(15) ä3,
1calcd
ˆ
[16] B. D. Hosangadi, R. H. Dave, Tetrahedron Lett. 1996, 35, 6375 6378.
[17] Crystallographic summary for 1: Colorless prisms were grown from
1.30 gcmÀ3, m ˆ 0.094mmÀ1, F(000) ˆ 1704. A total of 15166 reflec-
tions were measured, 9426 unique (Rint ˆ 0.079), on a Nonus Kappa
CCD using graphite monochromatized MoKa radiation (l ˆ
0.71073 äat 153 K. The structure was refined on F2 to an Rw ˆ 0.171,
with a conventional R ˆ 0.0827 (3989 reflections with Fo > 4[s(Fo)]),
and a goodness of fit ˆ 1.14 for 542 refined parameters.
≈
ethanol, triclinic, P1 (No. 2), Z ˆ 2 in a cell of dimensions: a ˆ
10.9063(2), b ˆ 12.0443(3), c ˆ 12.9586(3) ä, a ˆ 75.062(1), b ˆ
81.897(1), g ˆ 67.011(1)8, Vˆ 1512.52(6) ä3, 1calcd ˆ 1.24 gcmÀ3, m ˆ
0.289mmÀ1, F(000) ˆ 792. A total of 10351 reflections were measured,
6894 unique (Rint ˆ 0.026), on a Nonus Kappa CCD using graphite
monochromatized MoKa radiation (l ˆ 0.71073 ä) at 153 K. The
structure was refined on F2 to an Rw ˆ 0.123, with a conventional
R ˆ 0.0486 (4500 reflections with Fo > 4[s(Fo)]), and a goodness of
fit ˆ 1.02 for 380 refined parameters.
[19] G. T. Crisp, T. P. Bubner, Tetrahedron 1997, 53, 11881 11898; M.
Barzoukas, A. Fort, G. Klein, A. Boeglin, C. Serbutoviez, L. Oswald,
J. F. Nicoud, Chem. Phys. 1991, 153, 457 464.
[18] Crystallographic summary for 2: Colorless laths were grown by slow
evaporation from a 3:1 solution of ethanol/benzene, monoclinic, P21/n
Received: December 13, 2001 [F3737]
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