Diastereoselective cyclization in chiral diarylethene crystals: Polymorphism and selectivity

Article abstract of DOI:10.1021/ol034440h

(Matrix presented) An optically active photochromic diarylethene, (s)-1-(2-methyl-5-phenyl-3-thienyl)-2-[2-methyl-5-(4-(3-methyl-1-penten-1-yl) phenyl)-3-thienyl]-perfluorocyclopentene ((S)-1a), was synthesized. (S)-1a formed two crystalline phases, α- an

Full text of DOI:10.1021/ol034440h

ORGANIC
LETTERS
2003
Vol. 5, No. 10
1769-1772
Diastereoselective Cyclization in Chiral
Diarylethene Crystals: Polymorphism
and Selectivity
Satoshi Yamamoto, Kenji Matsuda, and Masahiro Irie*
Department of Chemistry and Biochemistry, Graduate School of Engineering,
Kyushu UniVersity, Hakozaki 6-10-1, Higashi-ku, Fukuoka 812-8581, Japan
irie@cstf.kyushu-u.ac.jp
Received March 12, 2003
ABSTRACT
An optically active photochromic diarylethene, (S)-1-(2-methyl-5-phenyl-3-thienyl)-2-[2-methyl-5-(4-(3-methyl-1-penten-1-yl)phenyl)-3-thienyl]-
perfluorocyclopentene ((S)-1a), was synthesized. (S)-1a formed two crystalline phases, r- and â-phases. The diarylethene underwent a
photochromic reaction in solution and even in the single-crystalline phase. In solution, no diastereoselection was observed. On the other
hand, in the â-crystalline phase, only one diastereomer (S,R,R)-1b was produced. No such diastereoselection was observed in the r-crystalline
phase.
In recent years, there has been considerable scientific interest
in crystalline-phase photochemistry.1 One unique aspect of
the crystalline-phase reaction is the topochemical reactivity.
The crystal lattices provide microenvironments for the
reactions with stereo-, regio-, and enantiospecificity. Enan-
tiospecific reactions take place in chiral crystals containing
chiral auxiliaries such as chiral host molecules2 or covalently
bonded chiral substituents.3 It should be noted that so-called
absolute asymmetric synthesis is possible when achiral
molecules spontaneously crystallize in a chiral space group.4
Photochromic diarylethenes undergo reversible cyclization/
cycloreversion photoreactions upon alternate irradiation with
UV and visible light.5 The photochemical conrotatory
cyclization produces two enantiomeric closed-ring isomers
((R,R)- and (S,S)-) originating from asymmetric carbon atoms
(Scheme 1). The photocyclization in solution, in general,
results in the formation of two enantiomers in equal amounts.
Even when a chiral substituent is introduced into the
Scheme 1. Photochromism of Diarylethenea
(1) (a) Photochemistry in Organized and Constrained Media; Rama-
murthy, V., Ed.; VCH: Weinheim, Germany, 1991. (b) Keating, A. E.;
Garcia-Garibay, M. A. In Molecular and Supramolecular Photochemistry;
Ramamurthy, V., Schanze, K., Eds.; Marcel Dekker: New York, 1998;
Vol. 2, pp 195-248. (c) Ramamurthy, V.; Venkatesan, K. Chem. ReV. 1987,
87, 433. (d) Toda, F. Acc. Chem. Res. 1995, 28, 480. (e) Gamlin, J. N.;
Jones, R.; Leibovitch, M.; Patrick, B.; Scheffer J. R.; Trotter J. Acc. Chem.
Res. 1996, 29, 203. (f) Tanaka, K.; Toda, F. Chem. ReV. 2000, 100, 1025.
(2) (a) Aoyama, H.; Hasegawa, M.; Omote, Y. J. Am. Chem. Soc. 1979,
101, 5343. (b) Toda, F.; Tanaka, K. J. Chem. Soc., Chem. Commun. 1986,
29, 4299. (c) Hosomi, H.; Ohba, S.; Tanaka, K.; Toda, F. J. Am. Chem.
Soc. 2000, 122, 1818.
a Photogenerated closed-ring form has two enantiomers, (R,R)-
and (S,S)-.
10.1021/ol034440h CCC: $25.00 © 2003 American Chemical Society
Published on Web 04/25/2003

Scheme 2
diarylethene, enrichment of one of the diastereomers hardly
Needle crystals of (S)-1a were obtained by recrystallization
from acetone. Two kinds of crystals, R- and â-phase crystals,
were obtained. The crystal structures are shown in Figure
2.12 Both crystals adopted chiral space group P21. There are
takes place.6
Some diarylethenes undergo photochromic reactions in the
single-crystalline phase.7 We have prepared a diarylethene
with a chiral substituent at the reactive carbon and examined
diastereoselection in solution as well as in the crystalline
phase.8 Although a diastereomeric mixture of the closed-
ring isomers was produced in solution, highly diastereo-
selective photocyclization took place in the single-crystalline
phase. The origin of the selectivity is ascribed to the restricted
conformation of the open-ring isomer in the crystal and
topochemical control. In this letter, we have prepared a
diarylethene (S)-1a having a chiral substituent at the end of
the molecule and examined the diastereoselection (Scheme
2).
The synthesis was performed by 1-(2-methyl-5-phenyl-3-
thienyl)-2-[2-methyl-5-(4-formylphenyl)-3-thienyl]perfluoro-
cyclopentene as the intermediate.9 Grignard reaction with
2-methylbutylmagnesium bromide followed by dehydration
reaction provided 1a. The structure of 1a was confirmed by
NMR, mass spectroscopy, and elemental analysis.10
Figure 1 shows the photochromic reaction of 1 in hexane.
Upon irradiation with 313 nm light, absorption at 586 nm
increased and reached a photostationary state. The solution
turned blue, which is the color of the closed-ring isomer 1b.11
The conversion at the photostationary state was 98%. Upon
irradiation with 578 nm light, the closed-ring isomer 1b was
completely returned back to the open-ring isomer 1a.
Figure 2. ORTEP drawing of the absolute configuration of (a)
R-(S)-1a and (b) â-(S)-1a. The asymmetric units are presented.
two molecules in the asymmetric unit of R-(S)-1a. One
molecule has a P configuration in the hexatriene of the
dithienylethene moiety, and the other molecule has an M
(3) (a) Schultz, A. G.; Taveras, A. G.; Taylar, R. E.; Tham, F. S.; Kulling,
R. K. J. Am. Chem. Soc. 1992, 114, 8725. (b) Sakamoto, M.; Takahashi,
M.; Hokari, N.; Fujita, T.; Watanabe, S. J. Org. Chem. 1994, 59, 3131. (c)
Ito, Y.; Kano, G.; Nakamura, N. J. Org. Chem. 1998, 63, 5643.
(4) Sheffer, J. R.; Garcia-Garibay, M. A. In Photochemistry of Solid
Surfaces; Matsuura, T., Anpo, M., Eds.; Elsevier: Amsterdam, 1989.
(5) (a) Irie, M. Chem. ReV. 2000, 100, 1685. (b) Matsuda, K.; Irie, M. J.
Am. Chem. Soc. 2001, 123, 9896. (c) Irie, M.; Fukaminato, T.; Sasaki, T.;
Tamai, N.; Kawai, T. Nature 2002, 420, 759.
(6) (a) Yamaguchi, T.; Uchida, K.; Irie, M. J. Am. Chem. Soc. 1997,
119, 6066. (b) Murguly, E.; Norsten, T. B.; Branda, N. R. Angew. Chem.,
Int. Ed. 2001, 40, 1752.
(7) (a) Irie, M.; Uchida, K.; Eriguchi, T.; Tsuzuki, H. Chem. Lett. 1995,
899. (b) Kobatake, S.; Yamada, T.; Uchida, K.; Kato, N.; Irie, M. J. Am.
Chem. Soc. 1999, 121, 2380. (c) Shibata, K.; Muto, K.; Kobatake, S.; Irie,
M. J. Phys. Chem. A 2002, 106, 209-214.
Figure 1. Absorption spectra of 1 in hexane (1.4 × 10-5 M). Open-
ring isomer (dashed line), closed-ring isomer (solid line), in the
photostationary state (dotted line).
1770
Org. Lett., Vol. 5, No. 10, 2003

configuration. Two molecules were pseudoracemates.13 In
the â-phase crystal, there was only one molecule in the
asymmetric unit, which has a P configuration. For all open-
ring isomers, the distances between reactive carbons were
in the range between 3.42 and 3.47 Å, which are sufficiently
short for the cyclization to take place in the crystalline phase.
Both crystals showed photochromic reactivity. The color-
less single crystal of R- and â-phase crystals turned dark
blue upon irradiation with 366 nm light. When observed
under polarized light, the blue color intensity was regularly
changed by rotating the crystal sample. This dichroic
behavior suggests that the closed-ring isomers are regularly
packed in the crystal. The blue color disappeared upon
irradiation with 578 nm light.
In the R-crystalline phase, diastereoselectivity was not
observed (Figure 3b). The two diastereomers were produced
in equal amounts. On the other hand, when the â-phase
crystal was irradiated with 366 nm light, one of the
diastereomers was produced predominantly (Figure 3c). The
diastereomeric excess was as high as >90%. On the basis
of the structure of the open-ring isomers in the crystal, the
main product is supposed to be (S,R,R)-1b.
The closed-ring isomer photogenerated in the â-single-
crystalline phase was separated using a chiral prepacked
column (Daicel CHIRALPAK OD-H, hexane). The recrys-
tallization of the separated closed-ring isomer in hexane
solution gave the black plate crystals. X-ray analysis of the
obtained crystal was carried out.14 The final configuration
of the photogenerated samples irradiated in the crystalline
state of the â-crystal is shown in Figure 4. Molecules
possessed the (S,R,R)-configuration.15
Diastereoselectivity in the photocyclization process was
examined in solution as well as in the two crystalline phases.
The photoirradiated sample was analyzed with a chiral HPLC
column (Daicel CHIRALCEL OD-RH, 2-propanol). The
HPLC charts are shown in Figure 3. As can be seen from
Figure 3. HPLC chromatogram of 1a monitored at 586 nm. (a)
Photocyclization in hexane solution. (b) Photocyclization reaction
in the R-single-crystalline phase. (c) Photoirradiation in the â-single-
crystalline phase.
Figure 4. ORTEP drawing of the absolute configuration of (S,R,R)-
1b. The asymmetric units are presented. (a) Top view. (b) Side
view.
Figure 3a, the closed-ring isomers produced in hexane
solution by irradiation with 313 nm light were a mixture of
equal amounts of two diastereomers, (S,S,S)-1b and (S,R,R)-
1b.
CD spectra of two diastereomers were measured. Figure
5 shows the CD spectra of the open-ring isomer (S)-1a and
(12) Crystal Data for r-(S)-1a: mp ) 130.5-131.0 °C, C33H28F6S2,
FW ) 602.67, monoclinic P21, a ) 15.7480(15) Å, b ) 8.6888(8) Å, c )
21.240(2) Å, â ) 102.789°, V ) 2834.2(5), Z ) 4, R (I > 2σ) ) 0.0479,
wR2 (all data) ) 0.1125, ø ) 0.06(13). â-(S)-1a: mp ) 127.0-130.0 °C,
C33H28F6S2, FW ) 602.67, monoclinic P21, a ) 10.3986(16) Å, b ) 8.6686-
(13) Å, c ) 16.054(3) Å, â ) 100.890°, V ) 1421.1(4), Z ) 2, R (I > 2σ)
) 0.0351, wR2 (all data) ) 0.0833, ø ) -0.02(5).
(8) (a) Kodani, T.; Matsuda, K.; Yamada, T.; Kobatake, S.; Irie, M. J.
Am. Chem. Soc. 2000, 122, 9631. (b) Matsuda, K.; Yamamoto, S.; Irie, M.
Tetrahedron Lett. 2001, 42, 7291.
(9) For details of the synthesis, see Supporting Information.
(10) (S)-1a: pale yellow crystal; 1H NMR (CDCl3, 400 MHz) δ 0.91 (t,
J ) 7 Hz, 3H), 1.09 (d, J ) 7 Hz, 3H), 1.42 (quintet, J ) 7 Hz, 2H), 1.96
(s, 3H), 1.97 (s, 3H), 2.20-2.23 (m, 1H), 6.13 (dd, J ) 16 Hz, 8 Hz, 1H),
6.34 (d, J ) 16 Hz, 1 H), 7.27-7.57 (m, 7H), 7.46 (d, J ) 8 Hz, 2H), 7.54
(d, J ) 8 Hz, 2H); UV-vis (hexane) λmax (ꢀ) 307 (44 000). Anal. Calcd
for C33H28F6S2: C, 65.76; H, 4.68. Found: C, 65.79; H, 4.75.
(11) (S)-1b (Mixture of (S,R,R)-1b and (S,S,S)-1b): 1H NMR (CDCl3,
400 MHz) δ 0.92 (t, J ) 8 Hz, 3H), 1.10 (d, J ) 7 Hz, 3H), 1.43 (quintet,
J ) 7 Hz, 2H), 1.38-1.47 (m, 1H), 2.18 (s, 6H), 6.21 (dd, J ) 16 Hz, 8
Hz, 1H), 6.36 (d, J ) 16 Hz, 1H), 6.66 (s, 1H), 6.68 (s, 1H), 7.27-7.60
(m, 9H); UV-vis (hexane) λmax (ꢀ) 586 (20 000), 344 (27 000).
(13) Jacques, J.; Collet, A.; Wilen, S. H. Enantiomers, Racemates and
Resolutions; Wiley & Sons: New York, 1981.
(14) Crystal Data for (S,R,R)-1b: C33H28F6S2, FW ) 602.67, monoclinic
P21, a ) 10.555(6) Å, b ) 25.402(13) Å, c ) 10.647(6) Å, â ) 91.697-
(6)°, V ) 2853(3), Z ) 4, R (I > 2σ) ) 0.0931, wR2 (all data) ) 0.2971,
ø ) -0.09(16).
(15) We obtained the (S,S,S)-1b crystal by separating the closed-ring
isomer photogenerated in solution. The result of the X-ray crystallography
is shown in Supporting Information.
Org. Lett., Vol. 5, No. 10, 2003
1771

The sign of the Cotton effect in the visible region was
opposite from our result. Our molecule has a phenyl group
at the 5-position of the thiophene ring, though the above
molecule does not have the phenyl group. This difference is
considered to affect the sign of the Cotton effect.8b
In conclusion, a chiral diarylethene (S)-1a was synthesized.
The diastereoselection was not observed in the photocycliza-
tion reaction in solution. The molecule formed two kinds of
crystals, R- and â-phases. In the R-(S)-1a crystal, no
diastereoselection was observed, but in the â-(S)-1a crystal,
only one closed-ring diastereomer was produced. It was
proved that the diastereoselectivity was dependent on the
crystal packing.
Acknowledgment. This work was supported by CREST
of Japan Science and Technology Corporation and by a
Grant-in-Aid for the 21st Century COE program (Functional
Innovation of Molecular Informatics) from the Ministry of
Education, Culture, Sports, Science, and Technology of
Japan.
Figure 5. CD spectra of 1 in hexane. Open-ring isomer (S)-1a
(gray line), closed-ring isomer (S,R,R)-1b (solid line), and (S,S,S)-
1b (dashed line).
the closed-ring isomers (S,S,S)-1b and (S,R,R)-1b. The open-
ring isomer has almost no CD signal. The CD signal of the
closed-ring isomers was much larger than that of the open-
ring isomer. The two spectra of closed-ring diastereomers
are mirror images. This result indicates that the CD spectra
of the closed-ring diastereomers mainly originates from the
diarylethene moiety.
Supporting Information Available: Experimental pro-
cedure for (S)-1a, the result of the X-ray crystallography of
(S,S,S)-1b, and X-ray crystallographic data for R-(S)-1a,
â-(S)-1a, (S,R,R)-1b, and (S,S,S)-1b (CIF). This material is
available free of charge via the Internet at http://pubs.acs.org.
OL034440H
Yokoyama et al. reported the CD spectra of the closed-
ring isomers of 1,2-bis(5-hydroxymethyl-2-methyl-3-thienyl)-
hexafluorocyclopentene, whose absolute structure is known.16
(16) Yokoyama, Y.; Hosoda, N.; Osano, Y. T.; Sasaki, C. Chem. Lett.
1998, 1093.
1772
Org. Lett., Vol. 5, No. 10, 2003