Water-assisted assembly of (E)-arylvinylpyridine hydrochlorides: Effective substrates for solid-state [2+2] photodimerization

Article abstract of DOI:10.1039/c1cc12572a

Water molecules assist the assembly of (E)-arylvinylpyridine hydrochlorides in a head-to-tail and face-to-face fashion by way of N-H...O hydrogen bonds in combination with cation-π interactions between the pyridinium and aromatic rings. Photolysis of the pyridinium salt hydrates provided synHT dimers in high yields.

Full text of DOI:10.1039/c1cc12572a

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COMMUNICATION
Water-assisted assembly of (E)-arylvinylpyridine hydrochlorides: effective
substrates for solid-state [2+2] photodimerizationw
Shinji Yamada* and Yuka Nojiri
Received 3rd May 2011, Accepted 20th June 2011
DOI: 10.1039/c1cc12572a
Water molecules assist the assembly of (E)-arylvinylpyridine
hydrochlorides in a head-to-tail and face-to-face fashion by way
of N–HÁ Á ÁO hydrogen bonds in combination with cation–p
interactions between the pyridinium and aromatic rings. Photo-
lysis of the pyridinium salt hydrates provided synHT dimers in
Fig. 1 Substrates for photodimerization.
high yields.
and anhydrous forms for the HCl salts. The hydrous forms,
1aÁHClÁ2H2O and 1bÁHClÁ3H2O, were prepared by recrystall-
ization of the corresponding HCl salts from MeOH. The
anhydrous forms, 1aÁHCl and 1bÁHCl, were obtained by
heating 1aÁHClÁ2H2O and 1bÁHClÁ3H2O, respectively, at
60 1C under a vacuum. The loss of the water molecules from
the hydrous forms was confirmed by thermogravimetric
analysis. The powdered crystals were placed between two
Pyrex plates and irradiated with a 250 W high-pressure
mercury lamp for 0.5–16 h. Table 1 gives a summary of the
results of the photochemical reactions.
Template-controlled solid-state [2+2] photodimerization of
olefins is a powerful technique for the construction of a stereo-
defined cyclobutane framework.1 Among several approaches
for assembly of olefins suitable for photodimerization reactions,
the use of hydrogen-bond-driven self-assembly is an attractive
strategy.2 For example, the formation of cocrystals of various
olefins with multifunctional molecules, such as diamines,3
1,3-dihydroxybenzenes,4 polycarboxylic acids5 or Rebek-imide,6
allows the parallel arrangement of double bonds, and has been
employed for regio- and stereoselective [2+2] photodimerization
reactions. Recently, it has been reported that small molecules
and ions, such as thiourea,7 and sulfate and bisulfate anions,8
serve as templates to preorient styrylpyridine derivatives in
crystals via the formation of hydrogen bond networks among
the templates and the substrates. The advantage of this new
type of template is that the hydrogen bond motifs can be easily
reorganized to fit the substrates.
We have previously reported that a cation–p interaction9 is
effective for the regio- and stereoselective [2+2] photo-
dimerization of (E)-styrylpyridines10 and azachalcones11 in
solution and in crystal form, respectively. In this communication,
we report our findings that water molecules assist the assembly
of (E)-arylvinylpyridine hydrochlorides in arrangements suitable
for photodimerization reactions by way of N–HÁÁÁO hydrogen
bonds in combination with cation–p interactions.
Styrylpyridine 1a gave no product and remained unchanged
even after irradiation for 16 h (entry 1). On the other hand,
irradiation of the HCl salt, 1aÁHClÁ2H2O, for 1h resulted in
quantitative conversion and formation of the synHT dimer 2a
in 91% yield accompanied by its isomers, 3a and 4a, as minor
products (entry 2). The structures of the products 2a–4a were
1
confirmed by comparison of the H NMR spectra with those
Table 1 Photolysis of 1a, 1b, 1aÁHCl, 1bÁHCl, 1aÁHClÁ2H2O and
1bÁHClÁ3H2O
The (E)-4-styrylpyridine (1a), (E)-4-(2-naphthyl)vinylpyridine
(1b) (Fig. 1), and their HCl salts were employed for the solid-
state [2+2] photodimerization reactions. There were hydrous
Products (%)a
Time/h Conv (%)a
2a, 2b
3a, 3b
4a, 4b
Entry Substrate
1
2
3
4
5
6
1a
16
1
16
16
0
99b
0
0
99
0
No reaction
5
No reaction
No reaction
1
Department of Chemistry, Ochanomizu University, Bunkyo-ku,
Tokyo 112-8610, Japan. E-mail: yamada.shinji@ocha.ac.jp;
Fax: +81-3-5978-5349; Tel: +81-3-5978-5349
w Electronic supplementary information (ESI) available: Experimental
details, the 1H NMR spectra for 2b–4b, the X-ray structures for 1a, 2b
and 4b, PXRD data for 1b and the thermogravimetric analysis data for
1a and 1b. CCDC 747473, 747476 and 818895. For ESI and crystallo-
graphic data in CIF or other electronic format see DOI: 10.1039/
c1cc12572a
91
2
1aÁHClÁ2H2O
1aÁHCl
1b
97
2
1bÁHClÁ3H2O 0.5
1bÁHCl 16
No reaction
a
1
Determined by H NMR spectra. (Z)-Isomer was obtained in 2%
b
yield.
c
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Chem. Commun., 2011, 47, 9143–9145 9143

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types of ring motifs, R46 (12) and R42 (8).14 The styrylpyridinium
cation interacts with a water molecule via a N–HÁÁÁO hydrogen
bond, as shown in Fig. 3. The adjacent molecules, related by
inversion, are linked to a different hydrogen bond network
system; therefore, two hydrogen bond networks assist one
column. The separation between the neighboring two olefinic
carbons is 3.797 A and 4.070 A, which is well within the Schmidt
requirement.15 This is consistent with the high reactivity and
selectivity observed in the solid-state photodimerization (Table 1,
entry 2). As no hydrogen bond is observed between the two
adjacent molecules, cation–p interactions between the pyridinium
and the phenyl groups are speculated to play an important role in
the formation of the head-to-tail stacked column structure, as
reported previously.10
Fig. 2 Crystal structure of 1aÁHClÁ2H2O viewed along the c-axis.
Although the crystal packing structure of 1aÁHCl is not
clear, its photostability suggests that such column structure
observed in 1aÁHClÁ2H2O is no longer retained. Comparisons
among the structural features of 1a, 1aÁHClÁ2H2O and 1aÁHCl
clearly show the important role of water molecules in assembly
of styrylpyridinium chloride.
reported.10 To elucidate whether or not water molecules affect
the reaction, the anhydrous 1aÁHCl was irradiated for 16 h. To
our surprise, 1aÁHCl demonstrated photostability similar to
that of 1a (entry 3).
Similar results were obtained for 2-naphtylvinylpyridine 1b;
i.e., irradiation of 1b gave no product (entry 4), whereas
photolysis of 1bÁHClÁ3H2O yielded the synHT dimer 2b in
an excellent yield accompanied by small amounts of 3b and 4b
(entry 5). The anhydrous salt, 1bÁHCl, was also photostable
(entry 6). The structures of 2b12 and 4b13 were determined by
X-ray structural analysis to be synHT and antiHT dimers,
respectively, and 3b was assigned as a synHH dimer on the
Fig. 4 shows the packing diagram of 1bÁHClÁ3H2O,16 which
is very similar to that of 1aÁHClÁ2H2O, although it contains
three equivalents of water molecules. The two adjacent
naphthylvinylpyridinium ions participate in different hydrogen
bond networks. The distances between the two molecules are
3.633 A and 3.728 A, which explains the high reactivity and
stereoselectivity. Similar to the case of 1aÁHCl, the crystal
structure of the anhydrous 1bÁHCl is not clear, albeit its
photostability suggests the destruction of the head-to-tail
column structure observed in 1bÁHClÁ3H2O.
1
basis of the H NMR and MS spectra.w
The significant effects of water molecules on the reactivities
and stereoselectivities in these solid-state photodimerization
reactions were elucidated by a comparison of the crystal
packing structures of 1a10 and 1aÁHClÁ2H2O.10 In the X-ray
packing diagrams of 1a, the molecules are arranged in a
head-to-head manner with a separation of 6.53A between
the two neighboring double bonds.w This indicates the absence
of any p–p interactions between these molecules, and explains
the photostability of 1a.
As the anhydrous 1aÁHCl and 1bÁHCl are hygroscopic, the
reversibility of their vapor uptake properties was evaluated.
Fig. 5 shows the changes in the PXRD patterns caused by the
dehydration and hydration processes of 1aÁHClÁ2H2O and
1aÁHCl, respectively. The PXRD pattern of the simulated
1aÁHClÁ2H2O is shown in Fig. 5a. After heating 1aÁHClÁ2H2O
at 100 1C for 6 h, the peaks of 1aÁHClÁ2H2O disappeared and
new broad peaks appeared, indicating the formation of a new
crystalline phase with lower crystallinity (Fig. 5b). Thermo-
gravimetric analysis of the resultant 1aÁHCl shows the
completion of the dehydration process. When the anhydrous
powder was kept in a desiccator at 58% relative humidity for
24 h, the PXRD pattern became much closer to that of the
simulated 1aÁHClÁ2H2O (Fig. 5c). After 48 h, the PXRD
pattern was in close agreement with that of the simulation
In contrast to 1a, the molecules of 1aÁHClÁ2H2O are
oriented parallel in a head-to-tail manner to form columns along
the c axis (Fig. 2 and 3). Channels are formed between the four
neighboring columns and occupied by water molecules and
chloride anions. These are linked one another by a combination
of O–HÁÁÁClÀ and O–HÁÁÁO hydrogen bonds containing two
Fig. 3 The head-to-tail stacking structure of styrylpyridinium self-
assembled by hydrogen bonding in 1aÁHClÁ2H2O.
Fig. 4 The head-to-tail stacking structure of naphthylvinylpyridinium
self-assembled by hydrogen bonding in 1bÁHClÁ3H2O.
c
9144 Chem. Commun., 2011, 47, 9143–9145
This journal is The Royal Society of Chemistry 2011

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This work was supported by a Grant-in-Aid for Scientific
Research (C) (No. 21550097) from the Japan Society for the
Promotion of Science.
Notes and references
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Synthesis: Toward
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2 For reviews, see: (a) L. R. MacGillivray, G. S. Papaefstathiou,
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T. Friscic, T. D. Hamilton, D.-K. Bucar, Q. Chu, D. B. Varshney
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MacGillivray, J. Org. Chem., 2008, 73, 3311–3317.
3 (a) Y. Ito, B. Borecka, J. Trotter and J. R. Scheffer, Tetrahedron
Lett., 1995, 36, 6083–6086; (b) Y. Ito, B. Borecka, G. Olovsson,
J. Trotter and J. R. Scheffer, Tetrahedron Lett., 1995, 36,
6087–6090; (c) Y. Ito, T. Kitada and M. Horiguchi, Tetrahedron,
2003, 59, 7323–7329; (d) T. Friscic and L. R. MacGillivray, Chem.
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Commun., 2005, 5748–5750; (e) A. Natarajan, J. T. Mague,
K. Venkatesan and V. Ramamurthy, Org. Lett., 2005, 7,
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2009, 11, 408–411.
4 (a) L. R. MacGillivray, J. L. Reid and J. A. Ripmeester, J. Am.
Fig. 5 The PXRD patterns for (a) simulated 1aÁHClÁ2H2O and
(b) anhydrous 1aÁHCl, and the PXRD patterns (c) after exposure
of 1aÁHCl to H2O vapor for 24 h or (d) 48 h.
Chem. Soc., 2000, 122, 7817–7818; (b) T. Friscic
L. R. MacGillivray, Chem. Commun., 2003, 1306–1307;
(c) X. Gao, T. Friscic and L. R. MacGillivray, Angew. Chem.,
Int. Ed., 2004, 43, 232–236; (d) T. Friscic, D. M. Drab and
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and
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L. R. MacGillivray, Org. Lett., 2004, 6, 4647–4650;
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L. R. MacGillivray, Angew. Chem., Int. Ed., 2010, 49, 4273–4277.
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6 D. B. Varshney, X. Gao, T. Friscic and L. R. MacGillivray,
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Angew. Chem., Int. Ed., 2006, 45, 646–650.
7 B. R. Bhogala, B. Captain, A. Parthasarathy and V. Ramamurthy,
J. Am. Chem. Soc., 2010, 132, 13434–13442.
8 G. K. Kole, G. K. Tan and J. J. Vittal, Org. Lett., 2010, 12,
128–131.
Scheme 1 Irradiation of 1aÁHClÁ2H2O and 1bÁHClÁ3H2O obtained
from anhydrous 1aÁHCl and 1bÁHCl.
9 (a) J. C. Ma and D. A. Dougherty, Chem. Rev., 1997, 97,
1303–1324; (b) S. Yamada, Org. Biomol. Chem., 2007, 5,
2903–2912.
10 S. Yamada, N. Uematsu and K. Yamashita, J. Am. Chem. Soc.,
2007, 129, 12100–12101.
(Fig. 5d). This clearly shows that the anhydrous 1aÁHCl was
rehydrated to produce hydrous 1aÁHClÁ2H2O. These observations
strongly suggest that the water molecules assist the assembly
of the styrylpyridinium cation in a head-to-tail and face-
to-face manner in combination with cation–p interactions
between the pyridinium and phenyl groups. Similar reversibility
was also observed between 1bÁHCl and 1bÁHClÁ3H2O.w
It should be noted that irradiation of the rehydrated
1aÁHClÁ2H2O and 1bÁHClÁ3H2O, obtained from anhydrous
1aÁHCl and 1bÁHCl, also afforded synHT dimers 2a and 2b
in 89% and 97% yields, respectively, indicating their high
crystallinity (Scheme 1).
11 S. Yamada and Y. Tokugawa, J.Am. Chem. Soc., 2009, 131,
2098–2099.
12 Crystal data for 2b: C34H26N2, M = 462.59, monoclinic, space
group P21, a = 10.5616(6), b = 9.5453(6), c = 13.5147(7) A,
b = 110.173(2)1, V = 1278.89(12) A3, Z = 2, Dcalcd = 1.201 g cmÀ3
,
m = 0.5350 mmÀ1 (Cu-Ka, l = 1.54178 A), T = 293 K. R1 = 0.0761
and wR2 = 0.2912 for 4523 unique reflections 42s(I). CCDC
747473.
13 Crystal data for 4b: C34H26N2, M = 462.59, orthorhombic, space
group Pbca, a = 22.5434(4), b = 8.91677(10), c = 49.7495(10) A,
V = 10000.4(3) A3, Z = 12, Dcalcd = 0.922 g cmÀ3, m = 0.4105 mmÀ1
In summary, we have shown that water molecules play a key
role in assembling arylvinylpyridinium salts. The hydrogen
bond networks assist the assembly of molecules in an anti-
parallel orientation in combination with cation–p interactions.
As the water provides flexible hydrogen bond networks, and is
easily removable and environmentally friendly, water-assisted
assembly would be of considerable utility in solid-state photo-
dimerization reactions. Studies of the substituent effect on
assembly are in progress and will be reported in due course.
(Cu-Ka,
l = 1.54178 A), T = 293 K. R1 = 0.0648 and
wR2 = 0.2166 for 9132 unique reflections 4 2s(I). CCDC 747476.
14 J. Bernstein, R. E. Davis, L. Shimoni and N.-L. Chang, Angew.
Chem., Int. Ed. Engl., 1995, 34, 1555–1573.
15 G. M. J. Schmidt, Pure Appl. Chem., 1971, 27, 647–678.
16 Crystal data for 1bÁHClÁ3H2O: C17H20N1O3Cl1, M = 321.80,
%
triclinic, space group P1, a = 7.0419(7), b = 11.0864(11), c =
12.0768(12) A, a = 64.825(3)1, b = 81.258(3)1, g = 81.852(3)1,
V = 840.22(15) A3, Z = 2, Dcalcd = 1.272 g cmÀ , m = 2.1117 mmÀ1
3
Cu-Ka, l = 1.54178 A, T = 293 K. R1 = 0.0994 and wR2 = 0.2563
for 2727 unique reflections 42s(I). CCDC 818895.
c
This journal is The Royal Society of Chemistry 2011
Chem. Commun., 2011, 47, 9143–9145 9145