Crystal Photodimerization Reactions of Spatially Engineered Isocoumarin Assemblies

Article abstract of DOI:10.1021/acs.cgd.5b00808

We report the single-crystal-to-single-crystal (SCSC) photodimerization of a sulfonamide isocoumarin. When recrystallized, this material forms centrosymmetrically related supramolecular dimers that assemble via the complementary features of molecular shap

Full text of DOI:10.1021/acs.cgd.5b00808

Communication
pubs.acs.org/crystal
Crystal Photodimerization Reactions of Spatially Engineered
Isocoumarin Assemblies
Published as part of the Crystal Growth & Design Margaret C. (Peggy) Etter Memorial virtual special issue.
Mihiri S. Weerasinghe, Steven T. Karlson, Yuhua Lu, and Kraig A. Wheeler*
Department of Chemistry, Eastern Illinois University, Charleston, Illinois 61920, United States
S
* Supporting Information
ABSTRACT: We report the single-crystal-to-single-crystal
(SCSC) photodimerization of a sulfonamide isocoumarin.
When recrystallized, this material forms centrosymmetrically
related supramolecular dimers that assemble via the comple-
mentary features of molecular shape and carboxyl···carboxyl
contacts. This prescribed motif persists despite the presence of
two-part whole-molecule disorder. Each disorder component is
involved in a unique set of hydrogen-bonding interactions, N−
H···OC versus N−H···OS, that propagate along the [111]
and [110] directions of the crystal, respectively. Despite the observed disorder, the overall recognition profile of this
supramolecular dimer remained intact, effectively promoting coplanar head-to-tail alignment with a separation of 3.4−4.1 Å
between the neighboring CC groups. UV illumination studies using the tail-irradiation technique produced a single
photodimer product in quantitative yield via a SCSC transformation.
the point that it is now part of the common vernacular of the
t has been more than two decades since the passing of
IProfessor Margaret “Peggy” Etter, and it is clear that her discipline.
Of particular interest to this contribution is Professor Etter’s
legacy to the science community remains firmly intact. This
special issue of Crystal Growth & Design dedicated to her offers
a testament to the impact and importance of her contributions.
Gauging importance may be difficult, but arguably the
interactions with those around her during her career stand
outher collaborators, friends, and students. One author of
this contribution (K.A.W.) was initially introduced to Peggy by
her first Ph.D. student, Thomas Panunto, while at the
University of Minnesota. This encounter proved immensely
rewarding. As an impressionable undergraduate student, he was
initiated into the world of molecular crystals and invited to join
the Etter research group with several projects to explore over
his two-year stay (1985−1987). The stories of Peggy’s warmth
and compassion hold in spades. She cared greatly for her
students and their science and somehow coerced the best out of
each to tell the most amazing stories of molecules and their
feats in crystals. This early experience fostered his interest in
the organic solid state that continues to this day.
Professor Etter provided an early voice that articulated the
importance and utility of molecular crystals to a wide range of
disciplines. Her distinctively creative approach to understanding
molecular associations has been critical in paving the way for
future generations to systematically explore nonbonded
contacts. Moreover, her approach to cocrystalline materials
continues to inspire the design of new functional materials (e.g.,
pharmaceuticals and high-energy materials), and her seminal
work on the systematics of hydrogen-bonding motifs via graph-
set theory1 has permeated much of the structural sciences to
early attention to solid-state transformations in organic crystals.
In nine publications spanning 16 years (1976−1992), Professor
Etter and her collaborators explored a variety of reaction
landscapes, such as polymorphic phase changes, aromatic
substitution, and gas−solid reactions, as well as outcomes that
follow topotactic pathways.2 One example of the latter area
focused on an elegant description of the X-ray-induced single-
crystal-to-single-crystal (SCSC) reaction of 1-methoxy-1,2-
benziodoxolin-3-one.2i Using only diffraction photographs,
this study tracked the reactant-to-product crystalline phases
and established the relationship of molecular packing,
intermolecular coordination interactions, unit cell parameters,
and space group symmetry during the course of the reaction
process. Our recent work in the area of SCSC reactions builds
extensively on previous contributions such as Peggy’s
polyvalent iodine study, where an intimate understanding of
reaction details can be achieved by inspection of X-ray
diffraction patterns.3 The study reported here examines the
UV-initiated SCSC reaction of an arylsulfonamide benzopyrone
with predetermined supramolecular alignment.
Benzopyrones serve as the principal structural component of
a diverse group of plant-derived compounds exhibiting
Special Issue: Margaret C. (Peggy) Etter Virtual Memorial Issue
Received: June 10, 2015
Revised: August 18, 2015
© XXXX American Chemical Society
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cytotoxic and other regulatory behavior.4,5 These core frame-
works are distinguished by an aryl-fused unsaturated six-
membered oxygen heterocycle decorated with a carbonyl
group. The various possibilities for placement of the O,
−O−, and CC functions on this chemical backbone lead to
three possible isomers, classified as α- [coumarin (1) and
isocoumarin (2)] or γ-benzopyrones [chromone (3)] (Figure 1
Our interest in solid-state transformations over the past few
years has focused on the utility of a family of arylsulfonamides
(4) that favor fish-hook molecular topologies. When recrystal-
lized, these molecules align pairwise to give photoactive
supramolecular assemblies (Figure 2).3 UV illumination of
Figure 2. Design strategy for the preparation and potential
photochemical reactivity of arylsulfonamides 4 and 5.
Figure 1. (left) Isomeric benzopyrones and (right) possible
photoproducts from UV irradiation of isocoumarin (2).
these materials showed that the reacting centers and
component chirality effectively translate to enantiocontrolled
cyclobutane photoproducts in near quantitative yields. The
success of this approach ultimately relates to the unique
collection of amino acid (4a), sulfonyl (4b), and reactive
cinnamoyl (4c) molecular fragments. Both experimental
studies3 and a systematic search of the extant crystallographic
database3a revealed that these structural features ensure that
this chemical architecture takes on the required fish-hook
topologies and are largely unaffected by the R group or
molecular configuration. Additionally, while molecules of 4
possess several competing hydrogen-bond donor and acceptor
groups, these systems generate the prescribed dimeric motifs
via carboxyl···carboxyl interactions consistent with Etter’s 1991
hydrogen-bond hierarchy rules.1 It is worth noting that prior to
this empirical guide to functional group associations, the task of
predicting hydrogen-bonding patterns was largely impractical
because of a lack of fundamental understanding of the interplay
of strong and weak intermolecular interactions. Since that time,
extensive studies related to the persistence of hydrogen-
bonding patterns have served only to support, define, and
extend Peggy’s earlier findings.13
In the context of this study, combining the complementary
features of robust nonbonded contacts and conformational
preferences of our arylsulfonamides results in a versatile
structural tool that consistently delivers molecular assemblies
capable of undergoing topochemically controlled [2 + 2]
photodimerizations. Building on this previous achievement, we
recently turned our attention to merging the crystal packing
patterns observed for the compounds of 4 and benzopyrone
frameworks. Can the desired supramolecular dimer be
effectively applied to benzopyrone chromophores? Upon
consideration of this question and the practical aspects of
implementing such a strategy, isocoumarin fragment 5c
emerged from the design stage as a plausible isomorphic
replacement for cinnamoyl 4c. This approach couples the
benefits of 1,4-disubstituted aryl groups, pendant carboxyls, and
photoactive CC groups. Conceptually, merging these
structural features to give isocoumarin 5 provides an attractive
target that is synthetically accessible via covalent linkage of 5c
with racemic alanine [4a, R = ( )-Me] and sulfonyl 4b
fragments.
left). Because their therapeutic potential (e.g., inflammatory,
antimicrobial, phytotoxic, and cytotoxic applications) translates
to multiple diseases, extensive interest has also been directed at
the development of a wide-range of synthetic protocols for the
preparation of derivatives that include these isomeric subunits.5
Beyond pharmacological functions, compounds containing
benzopyrone subunits 1−3 also undergo UV-initiated inter-
molecular [2 + 2] cycloadditions. Solvent-assisted trans-
formations involving these materials typically generate a
complex blend of head-to-head (hth) and head-to-tail (htt)
photodimers with nearly indiscernible or modest selectivities
(Figure 1, right).6 For instance, reports from the past decade
show how irradiation of benzene solutions of coumarin
produced the four possible dimerization products in a hth:anti
htt:anti hth:syn htt:syn ratio of 4.2:91.3:2.3:2.3, while the same
reaction in ethylene glycol gave a 0:22:19:59 mixture.6b,7 These
outcomes, and those from molecular variants, are often
influenced by electronic and steric effects that can be further
enhanced by exploiting the property of molecular confinement
found in macrocyclic systems. Studies of macrocycles using
cucurbiturils,8 cyclodextrin,9 and Pd nanocages10 all show
promise in preorganizing coumarin synthons in solution for
selective or accelerated photodimerization processes.
Analogous reactions controlled by the supramolecular
features of molecular crystals provide a considerable advantage
over solution-enabled processes. For benzopyrones, this greater
return can be seen in the case of β-cyclodextrin and coumarin,
where irradiated crystals of the 2:3 complex resulted in a 3-fold
increase in the syn head-to-head (rccc) photodimer.9c,11 As a
whole, literature examples building on the molecular subunits
1−3 proceed with elevated reaction outcomes.12 These
successes stem from the use of multimolecular systems capable
of capturing pairs of favorably aligned benzopyrones in
crystalline frameworks. While this current technology offers
measurable progress to the field, the orientation of reacting
CC groups for photochemical [2 + 2] cycloaddition
reactions occurs by fortuitous routes rather than a specified
design strategy targeting a predetermined benzopyrone align-
ment. Thus, moving forward in this area will require
technological advances that explore a variety of approaches
for engineering the predisposed alignment of benzopyrone
derivatives.
The synthesis of isocoumarin ( )-5 proceeded by a five-step
reaction sequence (Figure 3). The key intermediate, chlor-
osulfonyl isocoumarin 6, was prepared using a previously
reported protocol starting from homophthalic acid (7) (see the
B
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Figure 3. Synthetic scheme for the preparation of ( )-5 showing the
expected supramolecular dimer and the outcome of UV irradiation.
Supporting Information for full details).14 Esterification to 8
followed by base-catalyzed annulation (9) and chlorosulfona-
tion gave isocoumarin 6. Subsequent addition of racemic
alanine and sulfonyl chloride 6 under mildly basic conditions
gave ( )-5 in 1.3% overall yield.
Since self-assembly of ( )-5 in the solid state should proceed
in a similar fashion as for homologues of sulfonamide 4, we
anticipated a comparable molecular recognition profile favoring
dimer formation and alignment of the olefinic groups.
Inspection of Figure 4a shows the asymmetric unit of ( )-5
with molecules arranged with the anticipated fish-hook
conformation, in which the carboxyl of the alanine fragment
is positioned directly beneath the isocoumarin aryl group (full
details of crystal structure data collection, solution, and
refinement are given in the Supporting Information). Even
though the structure exhibits two-part whole-molecule disorder
(65:35), this distinct topological landscape persists and
assembles with a second molecule of opposite handedness
using carboxyl···carboxyl interactions to give an inversion-
related supramolecular dimer (Figure 4b). Dimer formation
likely results from the complementary features of molecular
shape and hydrogen bonds that promote the coplanar head-to-
tail alignment with a separation of 3.4−4.1 Å between
neighboring CC groups.
Figure 4. Crystal structure of unreacted ( )-5 showing (a) the critical
fish-hook topology and whole-molecule disorder and (b) the distinct
hydrogen-bonding patterns for the two disordered components.
pursued the solid-state photochemistry of ( )-5 using the
tail-irradiation technique.15 This method illuminates samples at
much longer wavelengths than that of the π−π* transition of
the reacting chromophores and under special circumstances can
provide opportunities to pursue reactions as SCSC trans-
formations. With this method, a sample of ( )-5 was processed
with a 200 W Xe(Hg) arc lamp fitted with a 360 nm cut-on
optical filter. The results of this study (Figure 5) show that a
single crystal of the starting material was converted
quantitatively to the photodimer after 8 h of UV irradiation.
Comparison of the unit cell parameters and space group
symmetries of the unreacted and photodimer crystalline phases
suggests that molecular motion resulting from the trans-
formation is isolated to the local reaction sites in the crystal.
Close inspection of the crystal structure of the UV-irradiated
( )-5 revealed that the disorder present in the reactant phase is
effectively transferred to the product during the photochemical
process. As shown in Figure 6a, the modeled disorder
corresponds to positioning of the sulfonamide−alanine frag-
ment over two sites. The proportion of this two-part disorder
(molecules A and B) is equivalent to that refined in the product
crystal (65:35 ratio). Since SCSC transformation are rare, it is
The two disordered components present in the crystal
structure (molecules A and B) participate in distinctly different
molecular associations. In the case of molecule A, adjacent
hydrogen-bonded dimers link via C(8) N−H···OC contacts
[N···O, 3.18(2) Å; N−H···O, 154(3)°] to give undulating
motifs (Figure 4b). These molecular chains propagate along the
[111] axis and are constructed from alternating dimers related
by c-glide symmetry. By contrast, dimers of disordered
component B assemble using N−H···OS contacts [N···O,
3.16(2) Å; N−H···O, 177(3)°] to form centrosymmetrically
related R22(8) motifs. This set of hydrogen bonds also generates
molecular chains; however, such patterns are derived from
translationally related dimers that extend along the [110]
direction of the crystal.
The molecular and crystal structures of ( )-5 support the
use of this material in further photochemical studies. The
observed critical molecular topology gives rise to the desired
hydrogen-bonded dimers, which in turn offers a distinct
advantage for the design and use of spatially engineered C
C groups of neighboring isocoumarin fragments. As with
similar investigations focused on arylsulfonamides 4, we
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tions and hydrogen-bonding patterns observed in the unreacted
phases remain largely undisturbed after photodimerization
(Figure 6a,b) [N−H···OC (molecule A), N···O, 3.38(3) Å
and N−H···O, 145(3)°; N−H···OS (molecule B), N···O,
3.17(2) Å and N−H···O, 158(6)°].
In summary, a single crystal of a sulfonamide-decorated
isocoumarin underwent a controlled UV-initiated [2 + 2]
photocyclization reaction. To the best of our knowledge, this
contribution represents a first for benzopyrone (i.e., coumarin,
isocoumarin, or chromone) photodimerizations where the
reaction outcome follows from spatially engineered reactants.
Previous reports on benzopyrones provide valuable insight into
the reaction patterns retrieved from both solution- and solid-
state-enabled processes, with recent advances directed at
improving the product selectivity and yield. Even so, currently
there exists no reliable strategy to control the spatial orientation
of neighboring reaction centers. Using the design elements of
molecular shape and hydrogen bonds, this study assembled
pairs of (R)-5 and (S)-5 molecules into prescribed inversion-
related supramolecular dimers that favorably align the olefin
groups of neighboring isocoumarin fragments. Upon UV
irradiation of ( )-5, the material experiences a SCSC [2 + 2]
transformation in quantitative yield that is supported by the
crystal structures of the unreacted and photodimer phases.
Finally, we emphasize that this work further highlights the
opportunities available for organizing the close proximity of
molecular pairs. While our current use of this strategy offers
distinct advantages for accessing controlled photodimerization
reactions of arylsulfonamides, future developments could
broaden this approach to include additional chemical frame-
works and applications.
Figure 5. Single-crystal UV irradiation of ( )-5 showing the
supramolecular dimer of the unreacted phase and photodimerization
of adjacent isocoumarin fragments (only the major disorder
component shown for clarity).
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.cgd.5b00808.
■
S
Experimental procedures, spectral data, and crystallo-
graphic data (PDF)
AUTHOR INFORMATION
Corresponding Author
* Tel: 01 217 581 3119. E-mail: kawheeler@eiu.edu.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by the National Science Foundation
(CHE-0957391 and CHE-0722547) and Eastern Illinois
University. Thanks are extended to Bruce Foxman (Brandeis
University) and Bruce Noll (Bruker AXS) for helpful
discussions and to Arnold Rheingold (University of California,
San Diego) for important X-ray experimental contributions.
Figure 6. Single-crystal UV irradiation of ( )-5 showing (a) the
asymmetric unit and (b) hydrogen-bonding patterns of the disordered
components.
REFERENCES
(1) Etter, M. C. J. Phys. Chem. 1991, 95, 4601−4610.
■
(2) (a) Ojala, W. H.; Etter, M. C. J. Am. Chem. Soc. 1992, 114,
10288−10293. (b) Etter, M. C.; Frankenbach, G. M.; Bernstein, J.
Tetrahedron Lett. 1989, 30, 3617−3620. (c) Etter, M. C.; Lipkowska,
Z. U.; Precigoux, G.; Leroy, F.; Decoret, C.; Bayard, F.; Royer, J.;
Vicens, J. Mol. Cryst. Liq. Cryst. 1988, 161, 67−76. (d) Vicens, J.;
Decoret, C.; Royer, J.; Etter, M. C. Isr. J. Chem. 1985, 25, 306−311.
(e) Etter, M. C. Mol. Cryst. Liq. Cryst. 1983, 93, 95−100. (f) Etter, M.
worthy of note that the presence of molecule disorder inherent
to this system does not inhibit the production of the
photoproduct but rather serves as two reaction sites for
photodimerization to occur. Moreover, the molecular orienta-
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Crystal Growth & Design
Communication
C. J. Chem. Soc., Perkin Trans. 2 1983, 115−121. (g) Etter, M. C.;
Siedle, A. R. Mol. Cryst. Liq. Cryst. 1983, 96, 35−38. (h) Errede, L. A.;
Etter, M. C.; Williams, R. C.; Darnauer, S. M. J. Chem. Soc., Perkin
Trans. 2 1981, 233−238. (i) Etter, M. C. J. Am. Chem. Soc. 1976, 98,
5331−5339.
(3) (a) Lu, Y.; Bolokowicz, A. J.; Reeb, S. A.; Wiseman, J. D.;
Wheeler, K. A. RSC Adv. 2014, 4, 8125−8131. (b) Yan, Z.;
Bolokowicz, A. J.; Collett, T. K.; Reeb, S. A.; Wiseman, J. D.;
Wheeler, K. A. CrystEngComm 2013, 15, 27−30. (c) Wheeler, K. A.;
Malehorn, S. H.; Egan, A. E. Chem. Commun. 2012, 48, 519−521.
(d) Grove, R. C.; Malehorn, S. H.; Breen, M. E.; Wheeler, K. A. Chem.
Commun. 2010, 46, 7322−7324.
(4) (a) Anand, P.; Singh, B.; Singh, M. Bioorg. Med. Chem. 2012, 20,
1175−1180. (b) Musa, M. A.; Cooperwood, J. S.; Khan, M. O. F. Curr.
Med. Chem. 2008, 15, 2664−2679. (c) Marshall, M. E.; Mohler, J. L.;
Edmonds, K.; Williams, B.; Butler, K.; Ryles, M.; Weiss, L.; Urban, D.;
Bueschen, A.; Markiewicz, M.; Cloud, G. J. Cancer Res. Clin. Oncol.
1994, 120, S39−S42. (d) Winter, E.; Lecerf-Schmidt, F.; Gozzi, G.;
Peres, B.; Lightbody, M.; Gauthier, C.; Ozvegy-Laczka, C.; Szakacs, G.;
Sarkadi, B.; Creczynski-Pasa, T. B.; Boumendjel, A.; Di Pietro, A. J.
Med. Chem. 2013, 56, 9849−9860.
Schultheiss, N. Assembly of Molecular Solids via Non-Covalent
Interactions. In Making Crystals by DesignMethods, Techniques and
Applications; Braga, D., Greponi, F., Eds.; Wiley-VCH: Weinheim,
Germany, 2007; Chapter 2.5, pp 209−240. (d) Aakeroy, C. B.;
Salmon, D. J. CrystEngComm 2005, 7, 439−448. (e) Hunter, C. A.
Angew. Chem., Int. Ed. 2004, 43, 5310−5324. (f) Bernstein, J.; Davis, R.
E.; Shimoni, L.; Chang, N. L. Angew. Chem., Int. Ed. Engl. 1995, 34,
1555−1575.
(14) Seitz, M.; Pluth, M. D.; Raymond, K. M. Inorg. Chem. 2007, 46,
351−353.
(15) (a) Benedict, J. B.; Coppens, P. J. Phys. Chem. A 2009, 113,
3116−3120. (b) Khan, M.; Enkelmann, V.; Brunklaus, G. Cryst.
Growth Des. 2009, 9, 2354−2362. (c) Abdelmoty, I.; Buchholz, V.; Di,
L.; Guo, C.; Kowitz, K.; Enkelmann, V.; Wegner, G.; Foxman, B. M.
Cryst. Growth Des. 2005, 5, 2210−2217.
(5) Coumarin: (a) Kontogiorgis, C.; Detsi, A.; Hadjipavlou-Litina, D.
Expert Opin. Ther. Pat. 2012, 22, 437−454. (b) Patil, P. O.; Bari, sS. B.;
Firke, S. D.; Deshmukh, P. K.; Donda, S. T.; Patil, P. A. Bioorg. Med.
Chem. 2013, 21, 2434−2450. Isocoumarin: (c) Pal, S.; Chatare, V.;
Pal, M. Curr. Org. Chem. 2011, 15, 782−800. (d) Yao, T.; Larock, R.
C. J. Org. Chem. 2003, 68, 5936−5942. (e) Ackermann, L.; Pospech, J.;
Graczyk, K.; Rauch, K. Org. Lett. 2012, 14, 930−933. (f) Chinnagolla,
R. K.; Jeganmohan, M. Chem. Commun. 2012, 48, 2030−2032.
Chromone: (g) Gaspar, A.; Matos, M. J.; Garrido, J.; Uriarte, E.;
Borges, F. Chem. Rev. 2014, 114, 4960−4992. (h) Zhao, Z.; Zhao, Y.;
Fu, H. Angew. Chem., Int. Ed. 2011, 50, 3769−3773.
(6) (a) Sakamoto, M.; Kanehiro, M.; Mino, T.; Fujita, T. Chem.
Commun. 2009, 2379−2380. (b) Yu, X.; Scheller, D.; Rademacher, O.;
Wolff, T. J. Org. Chem. 2003, 68, 7386−7399. (c) Kinder, M. A.;
Meyer, L.; Margaretha, P. Helv. Chim. Acta 2001, 84, 2373−2378.
(d) Kinder, M. A.; Margaretha, P. Org. Lett. 2000, 2, 4253−4255.
(7) Wolff, T.; Gorner, H. Phys. Chem. Chem. Phys. 2004, 6, 368−376.
(8) Pemberton, B. C.; Barooah, N.; Srivatsava, D. K.; Sivaguru, J.
Chem. Commun. 2010, 46, 225−227.
(9) (a) Asahara, H.; Iwamoto, T.; Kida, T.; Akashi, M. Tetrahedron
Lett. 2013, 54, 688−691. (b) Zhang, Q.; Qu, D.-A.; Wu, J.; Ma, X.;
Wang, Q.; Tian, H. Langmuir 2013, 29, 5345−5350. (c) Moorthy, J.
N.; Venkatesan, K.; Weiss, R. G. J. Org. Chem. 1992, 57, 3292−3297.
(10) Karthikeyan, S.; Ramamurthy, V. J. Org. Chem. 2006, 71, 6409−
6413.
(11) Brett, T. J.; Alexander, J. M.; Clark, J. L.; Ross, C. R., II;
Harbison, G. S.; Stezowski, J. J. Chem. Commun. 1999, 1275−1276.
(12) (a) Dawn, S.; Dewal, M. B.; Sobransingh, D.; Paderes, M. C.;
Wibowo, A. C.; Smith, M. D.; Krause, J. A.; Pellechia, P. J.; Shimizu, L.
S. J. Am. Chem. Soc. 2011, 133, 7025−7032. (b) Moorthy, J. N.;
Venkatesan, K. J. Org. Chem. 1991, 56, 6957−6960. (c) Tanaka, K.;
Toda, F. J. Chem. Soc., Perkin Trans. 1 1992, 943−944. (d) Tanaka, K.;
Toda, F.; Mochizuki, E.; Yasui, N.; Kai, Y.; Miyahara, I.; Hirotsu, K.
Angew. Chem., Int. Ed. 1999, 38, 3523−3525. (e) Tanaka, K.;
Mochizuki, E.; Yasui, N.; Kai, Y.; Miyahara, I.; Hirotsu, K.; Toda, F.
Tetrahedron 2000, 56, 6853−6865. (f) Zhao, D.; Sun, J.; Ding, K.
Chem. - Eur. J. 2004, 10, 5952−5963. (g) Gnanaguru, K.; Ramasubbu,
N.; Venkatesan, K.; Ramamurthy, V. J. Org. Chem. 1985, 50, 2337−
2346. (h) Vishnumurthy, K.; Guru Row, T. N.; Venkatesan, K. J.
Chem. Soc., Perkin Trans. 2 1996, 1475−1478. (i) Kinder, M. A.; Kopf,
J.; Margaretha, P. Tetrahedron 2000, 56, 6763−6767. (j) Natarajan, A.;
Ramamurthy, V. Solvent-Free Photosynthesis of Cyclobutanes:
Photodimerization of Crystallline Olefins. In The Chemistry of
Cyclobutanes; Rappoport, Z., Liebman, J. F., Eds.; John Wiley &
Sons: Chichester, U.K., 2006; Chapter 18, pp 807−872.
(13) (a) Braga, D.; Maini, L.; Grepioni, F. Chem. Soc. Rev. 2013, 42,
7638−7648. (b) Musumeci, D.; Hunter, C. A.; Prohens, R.; Scuderi,
S.; McCabe, J. F. Chem. Sci. 2011, 2, 883−890. (c) Aakeroy, C. B.;
E
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