Diastereospecific photochemical dimerization of a stilbene-containing daisy chain monomer in solution as well as in the solid state

Article abstract of DOI:10.1002/anie.200390296

A crown ether/dialkylammonium ion hybrid containing a stilbene group self-assembles into a [c2]daisy chain-like pseudorotaxane, the solid-state superstructure of which was confirmed by X-ray crystallography. Upon irradiation, the pseudorotaxane undergoes

Full text of DOI:10.1002/anie.200390296

Communications
Supramolecular Photodimerization
Diastereospecific Photochemical Dimerization of
a Stilbene-Containing Daisy Chain Monomer in
Solution as well as in the Solid State**
Dafni G. Amirsakis, Arkadij M. Elizarov,
Miguel A. Garcia-Garibay,* Peter T. Glink,
J. Fraser Stoddart,* Andrew J. P. White, and
David J. Williams*
The solid-state [2þ2] photochemical dimerization[1] of olefins
such as stilbenes is a highly efficient method for the stereo-
specific synthesis of cyclobutanes. In solution, however, the
photochemical reactions of such olefins generally result in
mixtures of products. For example, irradiation of trans-
stilbene in solution leads to several products: trans-to-cis
isomerization yields cis-stilbene, which then can undergo
electrocyclic ring closure to form dihydrophenanthrene,
which, in the presence of oxygen, is oxidized to phenan-
threne[2] while [2þ2] cycloaddition of trans-stilbene yields[3]
cyclobutane products with both syn-anti-syn and all-anti
stereochemistries. The reaction rates, yields, and the distri-
bution of products from photochemical reactions are depend-
ent on the choice of solvent.[4] For example, in nonpolar
solvents, such as benzene, trans-to-cis isomerization of
stilbenes is favored over a very slow dimerization process.[3]
In more polar solvents, such as methanol or water, hydro-
phobic interactions and possibly aromatic p-p stacking
interactions lead to relatively rapid formation of a cyclo-
butane ring as the major, albeit low-yielding, reaction path-
way, but with very little stereo- or regiocontrol.[4] Supra-
molecular assistance has provided solutions to the problem of
preorganizing pairs of olefins in solution, such that efficient
photochemical [2þ2] dimerizations may occur. Examples of
such supramolecular assistance in solution include 1) the
dimerization of stilbenes within the cavities of g-cyclodex-
trins[5] and cucurbit[8]uril,[6] 2) the use of hydrogen bonding to
orchestrate a reaction[7] between a bisammonium-substituted
dipyridylethylene and a bis([18]crown-6)-substituted stilbene
derivative, 3) using metal cations, such as K+ and Mg2+, to
template the reaction between the olefinic components of
[*] Prof. M. A. Garcia-Garibay, Prof. J. F. Stoddart, Dr. D. G. Amirsakis,
Dr. A. M. Elizarov, Dr. P. T. Glink
Department of Chemistry and Biochemistry
University of California, Los Angeles
405 Hilgard Avenue, Los Angeles, CA 90095-1569 (USA)
Fax: (+1)310-206-1843
E-mail: mgg@chem.ucla.edu
stoddart@chem.ucla.edu
Prof. D. J. Williams, Dr. A. J. P. White
Chemical Crystallography Laboratory
Department of Chemistry, Imperial College
South Kensington, London, SW7 2AY (UK)
Fax: (+44)207-594-5835
[**] We thank the National Science Foundation for funding this research
(CHE 9910199) which was also supported in part by an equipment
grant (CHE 9974928).
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derivatized crown ether molecules,[8] and 4) the encapsulation
and reaction[9] of acenaphthylenes and naphthoquinones
within self-assembled coordination cages.
converted using triphenylphosphane and N-chlorosuccini-
mide (NCS) into the chloride 5, which in turn was converted
by a Finkelstein reaction[16] into the iodide 6, which under-
went nucleophilic substitution to give the triphenylphospho-
nium iodide 7-I. A Wittig reaction[17] between 7-I and (2-
formyl)dibenzo[24]crown-8[14b] 8 gave the corresponding
stilbene derivative E-9. The Boc protecting groups were
removed using trifluoroacetic acid to give E-2-H·O2CCF3.
Single crystals were obtained by layer diffusion of hexanes
into a solution of E-2-H·O2CCF3 in CH2Cl2. The X-ray
structure[18] of E-2-H·O2CCF3 reveals the formation
(Figure 1) of a centrosymmetric [c2]daisy chain wherein the
For successful dimerizations to occur in the solid state, the
olefinic units must be aligned in a parallel manner with
centroid···centroid separations[10] of about 3.5–4.2 Š. Supra-
molecular approaches have been used successfully to align
stilbenes in the solid state, and their corresponding cyclo-
butane products have been obtained stereospecifically after
photoirradiation.[11] Recently, we reported[12] a highly stereo-
specific, solid-state, [2þ2] photocycloaddition between two
bis(dialkylammonium ion)-substituted stilbene dications in a
crystalline, doubly encircled and double-stranded, 2:2
host–guest complexwith bisparaphenylene[34]crown-
10. Although this and other examples of supramolec-
ular preorganization in the solid state are highly
efficient methods for the diastereospecific preparation
of syn-anti-syn-substituted cyclobutanes, solid-state
reactions do have their drawbacks, such as the need
to obtain crystalline substrates, their relatively slow
rates of reaction, and the difficulty in scaling reactions
up to preparatively useful levels. As a result, it is
important to find equally efficient methods for the
dimerization of olefins—with both high stereo- and
regiospecificity—in solution. Herein we describe a
stilbene-containing crown ether/dialkylammonium ion
hybrid that self-assembles into a [c2]daisy-chain-like
pseudorotaxane both in solution as well as in the solid
state. In this complex, the stilbene units are aligned in a
head-to-tail manner with their olefinic groups posi-
tioned for efficient diastereospecific photochemical
dimerizations.
Supramolecular and molecular daisy-chain-like
Figure 1. Ball-and-stick representation of the [c2]daisy chain formed by a pair of [E-2-H]+
entities[13] are becoming increasingly more appealing
targets in synthesis. Previously, we demonstrated that
1-H·O2CCF3—a self-complementary dialkylammo-
À
ions. Hydrogen-bonding interactions X···O, H···O [Š], X H···O [8]: a: 2.96, 2,17, 147; b:
À
2.98, 2.25, 138; c: 3.25, 2.37, 165; d: 3.21, 2.35, 146; the C H···p interaction e has H···p
À
2.86 Š and C H···p 1538; the p···p interaction f has centroid···centroid and mean interpla-
nium salt incorporating
(DB24C8) unit—forms dimers in
a
dibenzo[24]crown-8
head-to-tail
nar separations of 3.96 and 3.38 Š, respectively, the rings are inclined by approximately
88; the centroid···centroid distance g is 3.94 Š and the planes of the olefinic groups are
separated by about 3.29 Š.
a
manner, in relatively nonpolar solvents and in the
solid state, in which the NH2+ unit of one monomer is
positioned inside the DB24C8 unit of another, and vice
versa.[14] As a consequence of the asymmetric nature of the
substitution of one of the catechol units of 1-H·O2CCF3, two
diastereoisomeric [c2]daisy-chain-like complexes (Sche-
dibenzylammonium component of one molecule is threaded
through the polyether ring of the other and vice versa
(Figure 1). This mutual threading is accompanied by an
essentially parallel stacking of the trans-stilbene units of the
two component molecules such that the centers of the two
trans olefinic bonds are held at 3.94 Š from each other (see
Figure 2)—a geometry that should facilitate subsequent
1
me 1a) are observed to interconvert slowly on the H NMR
time-scale at room temperature. In the solid state, pairs of the
trisubstituted catechol rings of 1-H·O2CCF3 are aligned in a
parallel manner with a centroid···centroid separation of
3.55 Š. This observation prompted us to consider replacing
the central benzene unit of 1+ with a trans-stilbenoid unit
(namely, to prepare E-2-H·O2CCF3) with the anticipation that
photodimerization. The co-conformation of the [c2]daisy
+
À
À
chain is stabilized by a combination of N H···O, C H···O,
À
C H···p, and p···p interactions (interactions a–c, d, e, and f,
diastereoisomeric
cyclic
dimer
complexes
(E-2-
respectively, in Figure 1). The dimers form stepped stacks,
with the catechol ring in one dimer entering into a parallel p-p
stacking interaction with its symmetry-related counterpart in
the next; the centroid···centroid and mean interplanar sepa-
rations are 3.70 and 3.61 Š, respectively. These stacks and
their lattice-translated counterparts are arranged to form
H)2·(O2CCF3)2 (Scheme 1b) would form in which adjacent
trans-stilbene olefinic groups are aligned in a head-to-tail
manner at
a distance suitable for a photochemical
[2þ2] cycloaddition.
The stilbene-containing daisy-chain monomer E-2-
H·O2CCF3 was prepared according to the reaction sequence
summarized in Scheme 2. The benzylic alcohol[15] 4 was
À
sheets with the CF3CO2 ions and the CH2Cl2 solvent
molecules (both of which are disordered) intercalated
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Scheme 1. Cartoon and structural representations of [c2]daisy-chain-
like monomers, dimers, and photoadducts. a) 1-H·O2CCF3 dimerizes
in CD2Cl2 to form two diastereoisomeric [c2]daisy-chain-like dimers—a
meso and a d/l pair. In CD3SOCD3, the complexation is “turned off”
and only the monomer species 1-H·O2CCF3 is observed in solution.
b) Replacing the central benzene unit of 1-H·O2CCF3 with a stilbene
unit gives E-2-H·O2CCF3. We anticipated this salt will dimerize in
CD2Cl2 to form two diastereoisomeric [c2]daisy-chain-like dimers in
which the stilbene components are aligned and in proximity for a pho-
tochemical [2þ2] cycloaddition to occur in solution to give 3-
H2·2O2CCF3 with the syn-anti-syn configuration and head-to-tail regio-
chemistry as the sole cyclobutane-containing product.
between adjacent sheets, there being no immediately evident
electrostatic cation···anion interactions.
of the slow kinetics[20] of association and dissociation of the
subunits and the existence of diastereoisomeric [c2]daisy-
chain-like complexes; for example, two doublets at d = 6.28
and 6.43 ppm (J = 1.5 Hz) are observed for the aromatic
H1 proton, which suggests[21] that two diastereoisomeric
dimers of E-2-H·O2CCF3—presumably a meso one and a d/
l pair—exist in solution. Additionally, three of the four
expected doublets, with coupling constants of 16 Hz, appear
between d = 6.48 and 6.63 ppm; two of these signals corre-
spond to the olefinic protons of the major diasteroisomer of
(E-2-H)2·(O2CCF3)2 and one to the olefinic protons of the
minor one.[22] The upfield positioning of these signals suggests
that their protons experience a shielding environment, which
is expected in the [c2]daisy-chain-like complexes. The
1H NMR spectrum of E-2-H·O2CCF3 in CD3SOCD3 is much
less complicated (Figure 3b) since only the monomer species
E-2-H·O2CCF3 is expected[23] to exist in this highly polar
solvent.
A powdered crystalline sample of E-2-H·O2CCF3 was
placed between two pyrexmicroscope slides and irradiated
for 3 h, after which, an 1H NMR (500 MHz, CD3SOCD3)
spectrum (Figure 3c) of the product displayed a resonance at
d = 4.41 ppm. The chemical shift of this signal is characteristic
of the methine protons of a cyclobutane derivative—presum-
ably 3-H2·2O2CCF3—possessing a syn-anti-syn arrangement
of its tetraaryl substituents.[19] Additionally, the appearance of
only one cyclobutane signal in the 1H NMR spectrum
suggested that only one cyclobutane diastereoisomer had
been formed in quantitative yield. This observation confirmed
that the pairs of 3-H2+ dications exist in the crystal as [c2]daisy
chain dimers with eclipsed stilbene units, as illustrated in the
X-ray crystal structure (Figure 1).
A solution (3.8 mm) of the daisy chain monomer E-2-
1
H·O2CCF3 in CD2Cl2 was studied by H NMR spectroscopy.
The 1H NMR spectrum is very complex(Figure 3a) as a result
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CD3SOCD3.[24] It reveals that a significant change has
occurred upon irradiation. Most diagnostically, the signals
for the olefinic protons have disappeared and a broad singlet,
which represents the syn-anti-syn cyclobutane derivative 3-
H2·2O2CCF3, has once again appeared at d = 4.41 ppm. This
solution-state photodimerization appears to give rise to only
one diastereoisomer of the cyclobutane derivative 3-
H2·2O2CCF3 with greater than 95% conversion.[25,26]
1
Moreover, the H NMR spectrum (Figure 3d), obtained
after photoirradiation of E-2-H·O2CCF3 in a CD2Cl2 solution
is virtually identical to that (Figure 3c) obtained following the
solid-state photoirradiation of E-2-H·O2CCF3. Hence, not
only can it be inferred that [c2]daisy-chain-like pseudorotax-
anes are formed in solution as well as in the solid state, it can
also be concluded that the relative alignment of the stilbenoid
double bonds is roughly the same in the reactive solution-
state complex—namely, they are eclipsed[27]—as it is in the
solid-state dimer.
This fundamental investigation has established that
supramolecular assistance to the [2þ2] photodimerization
can be carried out in solution as well as in the solid state, and
that the photoreaction occurs with exactly the same stereo-
specificity in solution as it does in the solid state. This
observation is important in designing supramolecular systems
with multiple matching reaction centers for the construction
of large cluster-like and ribbon-like compounds incorporating
functionality.
Scheme 2. Synthesis of E-2-H·O2CCF3. Boc=tert-butoxycarbonyl.
TFA=trifluoroacetic acid.
Experimental Section
5: Addition of a solution of PPh3 (1.67 g, 6.40 mmol) in dry THF
(32 mL) to
a solution of N-chlorosuccinimide (NCS) (980 mg,
7.3 mmol) in dry THF (37 mL) resulted in the formation of a white
precipitate. A solution of 4[15] (1.0 g, 3.20 mmol) in dry THF (10 mL)
was added to the suspension, and the mixture was stirred overnight at
room temperature. The THF was evaporated and the residue was
subjected to column chromatography (SiO2; EtOAc/hexanes, 1:10), to
afford 5 (890 mg, 78%) as a clear oil. 1H NMR (CDCl3, 500 MHz,
298 K): d = 1.54 (s, 9H), 4.38 (brs, 2H), 4.46 (brs, 2H), 4.63 (s, 2H),
7.24 (brs, 2H), 7.27 (brs, 2H), 7.32 (brs, 1H), 7.33 (brs, 1H), 7.36–
7.30 ppm (m, 4H); 13C NMR (CDCl3, 125 MHz, 298 K): d = 28.5, 31.5,
45.6, 49.0, 79.9, 127.2, 127.4, 127.7, 127.9, 128.3, 128.5, 128.6, 128.8,
129.0, 129.1, 136.4, 155.9 ppm; HR-EIMS calcd for C20H25ClNO2
[MþH]+: m/z 346.1496, found: 346.1566.
6: A solution of 5 (371 mg, 1.07 mmol) in Me2CO (10 mL) was
added dropwise to a suspension of NaI (176 mg, 1.17 mmol) in
Me2CO (30 mL), and then stirred overnight at room temperature. The
salts were filtered off and the solvent was evaporated to give 6
(465 mg, 95%) as a light-brown oil, which was used without further
purification. 1H NMR (CDCl3, 500 MHz, 298 K): d = 1.32 (s, 9H),
4.12–4.21 (brm, 4H), 4.26 (s, 2H), 6.95–7.08 (brm, 4H), 7.12–
7.16 ppm (m, 5H); 13C NMR (CDCl3, 125 MHz, 298 K): d = 5.4, 28.1,
29.5, 49.4, 53.5, 127.0, 127.2, 127.6, 128.0, 128.3, 128.6, 128.7, 129.0,
129.1, 138.1, 155.6 ppm; HR-EIMS calcd for C20H25INO2 [MþH]+: m/
z 448.0852, found: 448.0921.
7-I: A solution of 6 (262 mg, 0.60 mmol) and PPh3 (173 mg,
0.66 mmol) in benzene (50 mL) was heated under refluxfor 2 h. After
cooling the reaction mixture down to room temperature, the
precipitate was filtered off to give 7-I (371 mg, 88%) as a white
solid. 1H NMR (CDCl3, 500 MHz, 298 K): d = 1.45 (s, 9H), 4.21–4.31
(brm, 4H), 5.24 (d, 2H, J = 13.1 Hz), 6.97–7.26 (brm, 4H), 7.26–7.34
(m, 5H), 7.61–7.69 ppm (m, 15H); 13C NMR (CDCl3, 125 MHz,
298 K): d = 28.3, 30.6 (JPC = 45.8 Hz), 48.4, 49.5, 117.5 (JPC = 85.3 Hz),
Figure 2. Space-filling representation of the [c2]daisy chain formed by
a pair of [E-2-H]+ ions. One monomer unit is red and the other blue;
the stilbenoid carbon–carbon double bond is yellow.
We investigated the [2þ2] photoaddition of E-2-
H·O2CCF3 in CD2Cl2 because of its strong tendency to
aggregate to afford cyclic noncovalent dimers in this solvent.
Thus, a solution of E-2-H·O2CCF3 in CD2Cl2 was placed in a
pyrexNMR tube, degassed by sonication, and then irradiated
through a cut-off filter (l > 350 nm) for about 20 min. Since
the 1H NMR spectrum of the reaction mixture in CD2Cl2 was
extremely complex, the solvent was evaporated and the
spectrum (Figure 1d) of the product was recorded in
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Figure 3. a) The 1H NMR spectrum of E-2-H·O2CCF3 in CD2Cl2 shows two major diastereoisomeric [c2]daisy-chain-like complexes in solution,
presumably the meso and d/l pairs. b) A much simpler 1H NMR spectrum of E-2-H·O2CCF3 in CD3SOCD3 where complexation is “turned off”. This
spectrum reveals how E-2-H·O2CCF3 looks in CD3SOCD3 before photochemical irradiation. c) 1H NMR spectrum of 3-H2·2O2CCF3 after solid-state
1
irradiation of crystalline E-2-H·O2CCF3. d) After irradiation of E-2-H·O2CCF3 in CD2Cl2, a H NMR spectrum of the photoproduct taken in
CD3SOCD3 reveals 3-H2·2O2CCF3 as the major product. A singlet centered on d=4.41 ppm corresponds to the methine protons present in a
cyclobutane ring with syn-anti-syn stereochemistry.
125.6, 127.2, 128.0, 128.2, 128.4, 130.1 (JPC = 12.5 Hz), 131.6 (JPC
=
0.35 mmol) in CH2Cl2 (20 mL) and the mixture was stirred for 1 h
before being evaporated to dryness to yield E-2-H·O2CCF3 as a white
solid (207 mg, 94%). 1H NMR (CD3SOCD3, 500 MHz, 298 K): d =
3.65–3.66 (m, 8H), 3.74–3.79 (m, 8H), 4.04–4.12 (m, 8H), 4.13–4.19
(m, 4H), 6.85–6.87 (m, 2H), 6.93–6.95 (m, 3H), 7.08 (dd, J = 8.3,
1.5 Hz, 1H), 7.14 (d, J = 16.3 Hz, 1H), 7.22 (d, J = 16.3 Hz, 1H), 7.24
(d, J = 1.5 Hz, 1H), 7.42–7.49 (m, 7H), 7.62 (d, J = 8 Hz, 2H),
9.18 ppm (brs, 2H); 13C NMR (CD3SOCD3, 125 MHz, 298 K): d =
50.4, 50.5, 69.0, 69.1, 69.4, 69.5, 70.7, 111.7, 114.0, 114.4, 120.9, 121.5,
125.9, 126.6, 129.0, 129.1, 129,4, 129.7, 130.2. 130.3, 130.4, 130.7, 132.1,
132.2, 138.4, 148.9, 158.3 ppm; HR-FABMS calcd for C40H48NO8 [E-
2]+: m/z 670.3408, found: 670.3374.
5.3 Hz), 134.3 (JPC = 9.8 Hz), 135.0 (JPC = 2.8 Hz), 137.6, 138.4,
155.7 ppm; HR-FABMS calcd for C38H39NO2P+ [M]+: m/z 572.2718,
found: 572.2713.
E-2-H·O2CCF3: A mixture of 7-I (371 mg, 0.53 mmol) and NaH
(51 mg, 2.1 mmol) in CH2Cl2 (25 mL) was stirred at ambient temper-
ature for 30 min and then a solution of 8 (253 mg, 0.53 mmol) in
CH2Cl2 (5 mL) was added slowly. The mixture was stirred for 20 h,
before 1n HCl (2 mL) was added to quench the reaction. The mixture
was partitioned between CH2Cl2 (25 mL) and H2O (20 mL). The
organic layer was washed with 1n HCl (2 ” 20 mL), dried (MgSO4),
and then evaporated to dryness. The residue was subjected to column
chromatography (SiO2; EtOAc/hexanes, 3:7) to afford E-9 as a clear
3-H2·2O2CCF3: Irradiation in solution: A solution of E-2-
H·O2CCF3 (2.6 mg, 3.8 mmol) in CD2Cl2 (1 mL) was degassed by
sonication in a pyrexNMR tube for about 20 min. The reaction
mixture was then irradiated for 20 min with UV light from a Hanovia
lamp in the presence of a filter (l > 350 nm). The solvent was
evaporated to give 3-2H2·2O2CCF3 as a white solid (2.6 mg, 95%).
1H NMR (CD3SOCD3, 500 MHz, 298 K): d = 3.45–3.49 (m, 8H),
3.58–3.59 (m, 8H), 3.64–3.65 (brs, 8H), 3.72 (brs, 8H), 3.88–3.89 (brs,
8H), 3.99–4.03 (brs, 16H), 4.41 (brs, 4H), 6.69 (brs, 4H), 6.74 (brs,
2H), 6.86–6.88 (m, 4H), 6.93–6.95 (m, 4H), 7.27 (s, 8H), 7.40 (s, 10H),
9.09 ppm (brs, 4H); 13C NMR (CD3SOCD3, 125 MHz, 298 K): d =
1
oil (269 mg, 66%). H NMR (CDCl3, 500 MHz, 298 K): d = 1.50 (s,
9H), 3.83–3.85 (m, 8H), 3.91–3.96 (m, 8H), 4.13–4.18 (m, 6H), 4.21–
4.23 (m, 2H), 4.34 (brs, 2H), 4.44 (brs, 2H), 6.84 (d, J = 8 Hz, 1H),
6.86–6.92 (m, 4H), 6.93 (d, J = 16 Hz, 1H), 6.99 (d, J = 16 Hz), 7.02–
7.04 (m, 1H), 7.06 (d, J = 1.8 Hz, 1H), 7.12–7.29 (m, 7H), 7.44 ppm (d,
J = 8 Hz, 2H); 13C NMR (CDCl3, 125 MHz, 298 K): d = 28.3, 31.5,
69.2, 69.3, 69.4, 69.7, 69.8, 80.0, 111.6, 113.7, 113.9, 120.3, 121.3, 126.3,
127.1, 128.2, 128.4, 130.8, 148.7, 148.8, 148.9, 155.9 ppm; HR-FABMS
calcd for C45H55NO10Na+ [MþNa]+: m/z 792.3749, found: 792.3718.
TFA (1 mL, 13 mmol) was added to a solution of E-9 (269 mg,
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46.5, 47.0, 49.9, 50.0, 68.8, 68.9, 69.5, 70.2, 114.4, 121.5, 128.8, 128.9,
129.3, 129.8, 130.2, 132.0, 133.7, 142.3, 146.9, 147.9, 148.8 ppm; HR-
FABMS calcd for C80H95N2O16·2TFA [3-H]+: m/z 1339.6603, found:
1339.6719. Irradiation in the solid state: Crystals were grown by
layering hexanes over a solution of E-2-H·O2CCF3 (5 mg) in CH2Cl2
(0.5 mL). The crystals were filtered, air-dried, placed between two
pyrexmicroscope slides, and then irradiated for about 3 h to give 3-
2H2·O2CCF3 (5 mg, 100%) as a white solid.
A. R. Dunn, L. M. Henling, J. W. Ziller, E. B. Lobkovsky, R. H.
Grubbs, J. Am. Chem. Soc. 1998, 120, 3641 – 3649; f) K. S. S. P.
Rao, S. M. Hubig, J. N. Moorthy, J. K. Kochi, J. Org. Chem. 1999,
64, 8098 – 8104; g) K. Tanaka, F. Toda, E. Mochizuki, N. Yasui, Y.
Kai, I. Miyahara, K. Hirotsu, Angew. Chem. 1999, 111, 3733 –
3736; Angew. Chem. Int. Ed. 1999, 38, 3523 – 3525; h) L. R.
MacGillivray, J. L. Reid, J. A. Ripmeester, J. Am. Chem. Soc.
2000, 122, 7817 – 7818; i) G. S. Papaefstathiou, A. J. Kipp, L. R.
MacGillivray, Chem. Commun. 2001, 2462 – 2463; j) L. R. Mac-
Gillivray, J. L. Reid, J. A. Ripmeester, G. S. Papaefstathiou, Ind.
Eng. Chem. Res. 2002, 41, 4494 – 4497; k) T. D. Hamilton, G. S.
Papaefstathiou, L. R. MacGillivray, CrystEngComm 2002, 4,
223 – 226; l) T. D. Hamilton, G. S. Papaefstathiou, L. R. MacGil-
livray, J. Am. Chem. Soc. 2002, 124, 11606 – 11607.
Received: September 30, 2002 [Z50266]
Keywords: dimerization · photochemistry · pseudorotaxane ·
.
solid-state reactions · structure-directed synthesis
[12] D. G. Amirsakis, M. A. Garcia-Garibay, S. J. Rowan, J. F.
Stoddart, A. J. P. White, D. J. Williams, Angew. Chem. 2001,
113, 4386 – 4391; Angew. Chem. Int. Ed. 2001, 40, 4256 – 4261.
[13] a) S. J. Rowan, S. J. Cantrill, J. F. Stoddart, A. J. P. White, D. J.
Williams, Org. Lett. 2000, 2, 759 – 763; b) M. C. JimØnez, C.
Dietrich-Buchecker, J.-P. Sauvage, A. De Cian, Angew. Chem.
2000, 112, 1351 – 1354; Angew. Chem. Int. Ed. 2000, 39, 1295 –
1298; c) M. C. JimØnez, C. Dietrich-Buchecker, J.-P. Sauvage,
Angew. Chem. 2000, 112, 3422 – 3425; Angew. Chem. Int. Ed.
2000, 39, 3284 – 3287; d) S.-H. Chiu, S. J. Rowan, S. J. Cantrill,
J. F. Stoddart, A. J. P. White, D. J. Williams, Chem. Commun.
2002, 2948 – 2949.
[14] a) P. R. Ashton, I. Baxter, S. J. Cantrill, M. C. T. Fyfe, P. T. Glink,
J. F. Stoddart, A. J. P. White, D. J. Williams, Angew. Chem. 1998,
110, 1344 – 1347; Angew. Chem. Int. Ed. 1998, 37, 1294 – 1297;
b) S. J. Cantrill, G. J. Youn, J. F. Stoddart, J. Org. Chem. 2001, 66,
6857 – 6872.
[1] For reviews on solid-state photochemistry, see a) M. Hasegawa,
Chem. Rev. 1983, 83, 507 – 518; b) V. Ramamurthy, K. Venka-
tesan, Chem. Rev. 1987, 87, 433 – 481; c) F. Toda, Acc. Chem. Res.
1995, 28, 480 – 486; d) J. N. Gamlin, R. Jones, M. Leibovitch, B.
Patrick, J. R. Scheffer, J. Trotter, Acc. Chem. Res. 1996, 29, 203 –
209; e) Y. Ito, Synthesis 1998, 1 – 32; f) A. E. Keating, M. A.
Garcia-Garibay in Organic and Inorganic Photochemistry (Eds.:
V. Ramamurthy, K. S. Schanze), Marcel Dekker, New York,
1998, pp. 195 – 248; g) K. Tanaka, F. Toda, Chem. Rev. 2000, 100,
1025 – 1074; h) L. R. MacGillivray, CrystEngComm 2002, 4, 37 –
41.
[2] a) F. B. Mallory, C. S. Wood, J. Gordon, L. C. Lindquist, M. L.
Saviz, J. Am. Chem. Soc. 1962, 84, 4361 – 4362; b) H. Meier,
Angew. Chem. 1992, 104, 1425 – 1576; Angew. Chem. Int. Ed.
Engl. 1992, 31, 1399 – 1420.
[3] a) H. Shechter, W. J. Link, G. V. D. Tiers, J. Am. Chem. Soc.
1963, 85, 1601 – 1605; b) H. Ulrich, D. V. Rao, F. A. Stuber,
A. A. R. Sayigh, J. Org. Chem. 1970, 35, 1121 – 1125; c) B. S.
Green, J. Heller, J. Org. Chem. 1974, 39, 196 – 201.
[4] a) M. S. Syamala, V. Ramamuthy, J. Org. Chem. 1986, 51, 3712 –
3715; b) Y. Ito, T. Kajita, K. Kunimoto, T. Matsuura, J. Org.
Chem. 1989, 54, 587 – 591.
[5] a) W. Herrmann, M. Schneider, G. Wenz, Angew. Chem. 1997,
109, 2621 – 2624; Angew. Chem. Int. Ed. Engl. 1997, 36, 2511 –
2514; b) W. Herrmann, S. Wehrle, G. Wenz, Chem. Commun.
1997, 1709 – 1710.
[15] P. R. Ashton, J. Becher, M. C. T. Fyfe, M. B. Nielsen, J. F.
Stoddart, A. J. P. White, D. J. Williams, Tetrahedron 2001, 57,
947 – 956.
[16] L. F. Tietze, T. Eicher in Reactions and Synthesis in the Organic
Chemistry Laboratory (Trans.: D. Ringe), University Science
Books, Mill Valley, CA, 1989, p. 48 – 49.
[17] S.-H. Chiu, S. J. Rowan, S. J. Cantrill, J. F. Stoddart, A. J. P.
White, D. J. Williams, Chem. Eur. J. 2002, 8, 5170 – 5183.
[18] Crystal
data
for
2-H·O2CCF3·HO2CCF3·1.5CH2Cl2:
[C40H48NO8](O2CCF3)·HO2CCF3·1.5CH2Cl2, Mr = 1025.2, tri-
ꢀ
clinic, space group P1 (no. 2), a = 10.195(1), b = 11.740(1), c =
[6] S. Y. Jon, Y. H. Ko, S. H. Park, H.-J. Kim, K. Kim, Chem.
Commun. 2001, 1938 – 1939.
21.690(2) Š, a = 95.39(1), b = 102.89(1), g = 100.59(1)8, V=
2462.5(4) Š3, Z = 2, 1calcd = 1.383 gcmÀ3, m(CuKa) = 2.41 mmÀ1
,
[7] a) S. P. Gromov, E. N. Ushakov, A. I. Vedernikov, N. A. Lobova,
M. V. Alfimov, Y. A. Strelenko, J. K. Whitesell, M. A. Fox, Org.
Lett. 1999, 1, 1697 – 1699; b) D. M. Bassani, V. Darcos, S.
Mahony, J.-P. Desvergne, J. Am. Chem. Soc. 2000, 122, 8795 –
8796; c) D. M. Bassani, X. Sallenave, V. Darcos, J.-P. Desvergne,
Chem. Commun. 2001, 1446 – 1447.
[8] a) S. Inokuma, T. Yamamoto, J. Nishimura, Tetrahedron Lett.
1990, 31, 97 – 100; b) S. P. Gromov, O. A. Fedorova, E. N.
Ushakov, A. V. Buevich, I. I. Baskin, Y. V. Pershina, B. Eliasson,
U. Edlund, M. V. Alfimov, J. Chem. Soc. Perkin Trans. 2 1999,
1323 – 1329; c) O. A. Fedorova, S. P. Gromov, M. V. Alfimov,
Russ. Chem. Bull. 2001, 50, 1970 – 1983.
T= 203 K, colorless prisms; 7292 independent measured reflec-
tions, F2 refinement, R1 = 0.105, wR2 = 0.277, 3751 independent
observed reflections (j Fo j > 4s j 2q ꢀ 1208), 675 parameters.
CCDC-191314 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge via
www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cam-
bridge Crystallographic Data Centre, 12 Union Road, Cam-
bridge CB21EZ, UK; fax: (+ 44)1223-336-033; or deposit@
ccdc.cam.ac.uk).
[19] The chemical shift of this signal at d = 4.41 ppm is consistent with
the syn-anti-syn isomer 3-H2·2O2CCF3, since other syn-anti-syn
tetraaryl-substituted cyclobutane derivatives have been reported
(see refs. [3], [6], [11f], and [12]) to exhibit resonance of the
corresponding ring proton in the range d = 4.10 to 5.00 ppm. In
contrast, the all-anti tetraaryl-substituted isomer is expected to
contain cyclobutane ring protons resonating between d = 3.50
and 3.80 ppm.
[20] P. R. Ashton, E. J. T. Chrystal, P. T. Glink, S. Menzer, C. Schiavo,
N. Spencer, J. F. Stoddart, P. A. Tasker, A. J. P. White, D. J.
Williams, Chem. Eur. J. 1996, 2, 709 – 728.
[21] Although we have depicted (Scheme 1) the major and minor co-
conformations of (E-2-H)2·(O2CCF3)2 to be those in which the
olefinic units of each monomer are eclipsed, there exists the
[9] M. Yoshizawa, Y. Takeyama, T. Kusukawa, M. Fujita, Angew.
Chem. 2002, 114, 1403 – 1405; Angew. Chem. Int. Ed. 2002, 41,
1347 – 1349.
[10] a) M. D. Cohen, G. M. J. Schmidt, F. I. Sonntag, J. Chem. Soc.
1964, 2000 – 2013; b) G. M. J. Schmidt, J. Chem. Soc. 1964, 2014 –
2021; c) G. M. J. Schmidt, Pure Appl. Chem. 1971, 27, 647 – 678.
[11] a) K. S. Feldman, R. F. Campbell, J. Org. Chem. 1995, 60, 1924 –
1925; b) Y. Ito, B. Borecka, J. Trotter, J. R. Scheffer, Tetrahedron
Lett. 1995, 36, 6083 – 6086; c) Y. Ito, B. Borecka, G. Olovsson, J.
Trotter, J. R. Scheffer, Tetrahedron Lett. 1995, 36, 6087 – 6090;
d) A. J. Blake, N. R. Champness, S. S. M. Chung, W.-S. Li, M.
Schröder, Chem. Commun. 1997, 1675 – 1676; e) G. W. Coates,
Angew. Chem. Int. Ed. 2003, 42, No. 10
ꢀ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1433-7851/03/4210-1131 $ 20.00+.50/0
1131

Communications
possibility of other co-conformations being populated in which
the olefinic units are oriented in staggered arrangements. Since
these staggered co-conformations are diastereoisomeric with
respect to the eclipsed ones, the well-resolved signals observed
for the olefinic protons suggest that if these co-conformations
are populated, then they are interconverting rapidly with the
eclipsed co-conformations on the 1H NMR time-scale at
500 MHz at 300 K.
[22] We reached this conclusion by analogy to the similar set of two
signals for the corresponding H1 proton of 1-H·O2CCF3 observed
in its 1H NMR spectrum in CD3CN. See ref. [14].
[23] The FAB mass spectrum of E-2-H·O2CCF3 in Me2SO reveals
peaks at m/z 692.52 (100%) and 1339.98 (10%), which corre-
spond to monomeric [E-2þNa]+ and a small amount of the
dimeric [(E-2)2-H]+, respectively. By contrast, the FAB mass
spectrum of E-2-H·O2CCF3 in CH2Cl2 reveals peaks at
m/z 670.34 (60%) and 692.33 (20%) which correspond to the
doubly
charged
[c2]daisy-chain-like
pseudorotaxane
[(E-2)2þHþNa]2+ and
a
small amount of the monomer
[E-2þNa]+, respectively.
[24] When a solution of E-2-H·O2CCF3 (3.8 mmol) was irradiated in
CD3SOCD3 (1 mL) for 20 min, trans-to-cis isomerization occur-
red to yield E-2-H·O2CCF3 and Z-2-H·O2CCF3 as the only two
species present in solution. No cyclobutane derivative was
1
observed in the H NMR spectrum. This result is not surprising
since no dimerization is expected to occur in CD3SOCD3. See
ref. [20].
[25] A slight impurity is suggested by the presence of a small signal at
d = 7.6 ppm in the 1H NMR spectrum, but this contaminant also
appears to be present in the initial sample of E-2-H·O2CCF3.
[26] It is worth noting that both the meso and d/l pair of diaster-
eoisomers of (E-2-H)2·(O2CCF3)2 yield the same head-to-head
and syn-anti-syn diastereoisomer of 3-H2·2O2CCF3. The meso
and d/l diastereoisomeric self-complexes of 3-H2·2O2CCF3 are
not observed in CD3SOCD3 because intramolecular hydrogen-
bonding interactions are eradicated. These two self-complexes
exist in less polar solvents, a feature that explains the compli-
cated nature of the 1H NMR spectrum of 3-H2·2O2CCF3 in
CD2Cl2.
[27] If the staggered co-conformations of (E-2-H)2·(O2CCF3)2 (see
ref. [22]) were capable of undergoing [2þ2] cycloaddition in
solution, we would expect to observe also the formation of the
all-anti cyclobutane diastereoisomer as a product.
1132
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Angew. Chem. Int. Ed. 2003, 42, No. 10