Diastereoselective cyclization of a diarylethene having a chiral N-phenylethylamide substituent in crystals

Article abstract of DOI:10.1016/S0040-4039(01)01495-2

A diarylethene which has an N-phenylethylcarbamoyl substituent at the periphery of 1,2-bis(2-methyl-5-phenyl-3-thienyl)hexafluorocyclopentene was synthesized. The diarylethene underwent a photochromic reaction both in solution and in the single-crystalline phase. The chiral substituent at the end of the molecule contributed to the intermolecular hydrogen bond formation in the crystal and the crystal adopted the chiral space group P2₁. In the crystalline phase photocyclization reaction, only one closed-ring diastereomer was produced, while the diastereoselection was not observed in solution.

Full text of DOI:10.1016/S0040-4039(01)01495-2

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 42 (2001) 7291–7293
Diastereoselective cyclization of a diarylethene having a chiral
N-phenylethylamide substituent in crystals
Kenji Matsuda, Satoshi Yamamoto and Masahiro Irie*
Department of Chemistry and Biochemistry, Graduate School of Engineering, Kyushu University, and CREST,
Japan Science and Technology Corporation, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan
Received 25 June 2001; revised 30 July 2001; accepted 10 August 2001
Abstract—A diarylethene which has an N-phenylethylcarbamoyl substituent at the periphery of 1,2-bis(2-methyl-5-phenyl-3-
thienyl)hexafluorocyclopentene was synthesized. The diarylethene underwent a photochromic reaction both in solution and in the
single-crystalline phase. The chiral substituent at the end of the molecule contributed to the intermolecular hydrogen bond
formation in the crystal and the crystal adopted the chiral space group P21. In the crystalline phase photocyclization reaction,
only one closed-ring diastereomer was produced, while the diastereoselection was not observed in solution. © 2001 Elsevier
Science Ltd. All rights reserved.
Photochromic compounds change their geometrical and
electronic structures upon irradiation with light of
appropriate wavelengths.1 When one of the isomers is
chiral, chiroptical properties are also changed by the
photochromic reaction.2 Photochromic diarylethenes
undergo cyclization/cycloreversion photoreactions.3
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
diarylethene, enrichment of one of the diastereomers
hardly takes place.4
solution, photocyclization was highly diastereoselective
in the single-crystalline phase. The origin of the selectiv-
ity is the restricted conformation of the open-ring iso-
mer in the crystal. In this letter we have introduced a
chiral substituent at the periphery of the molecule
which can form intermolecular hydrogen bonds to con-
trol the crystal structure.
We chose 1,2-bis(2-methyl-5-phenyl-3-thienyl)hexa-
fluorocyclopentene as the photochromic core because
this compound is known to undergo the photochromic
reaction in the single-crystalline phase.7 An N-
phenylethylcarbamoyl group was introduced at para
position of the phenyl group, and is capable of inter-
molecular hydrogen bond formation. The resulting
molecule is (S)-1a, as shown in Scheme 2. Compound
1a was prepared from 1-(2-methyl-5-phenyl-3-thienyl)-2
-(2-methyl-5-(4-formylphenyl)-3-thienyl)hexafluoro-
cyclopentene. Jones oxidation followed by treat-
ment with thionyl chloride afforded acyl chloride.
(S)-Phenylethylamine was mixed with the acyl
Some diarylethenes undergo photochromic reactions in
the single crystalline phase.5 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.6 Although a racemic
mixture of the closed-ring isomers was produced in
Scheme 1. Photochromism of diarylethene. The photogenerated closed-ring form has two enantiomers, (R,R) and (S,S).
* Corresponding author.
0040-4039/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(01)01495-2

7292
K. Matsuda et al. / Tetrahedron Letters 42 (2001) 7291–7293
Scheme 2.
tion of (S)-1a as shown in Fig. 2. The crystal also
contained solvent hexane.
chloride to give (S)-1a. The overall yield from aldehyde
to amide was 60%, and the structure was confirmed by
NMR, mass spectroscopy, and elemental analysis.8
The crystal also showed photochromic reactivity. The
colorless single crystal of (S)-1a turned dark blue upon
irradiation with 366 nm light. When observed under
polarized light, the blue color intensity regularly
changed upon rotation of the crystal sample. This
phenomenon suggests that the closed-ring isomers were
regularly packed in the crystal. The blue color disap-
peared upon irradiation with 578 nm light.
Upon irradiation with UV light, (S)-1a underwent a
cyclization reaction in hexane. Fig. 1 shows the absorp-
tion spectral change of compound (S)-1a in hexane.
Upon irradiation with 313 nm light a 582 nm band
increased and reached the photostationary state in 5
min. This is due to the formation of the closed-ring
isomer.9 The color of the solution changed from color-
less to blue. An isosbestic point was observed at 318
nm. The conversion from the open- to the closed-ring
isomers was 96% in the photostationary state. Upon
irradiation with 578 nm light, the spectrum converted
back to that of the starting material.
Diastereoselectivity in the cyclization process was
examined in solution and in the crystalline phase. The
photoirradiated sample was analyzed with a chiral
HPLC column (Daicel CHIRALCEL OD-H, hexane:2-
propanol:ethanol=90:9:1 volume ratio). 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. In the
crystalline phase reaction, one of the diastereomers was
dominant. Diastereomeric excess was as high as 82%
when the conversion was around 10%. The rather low
d.e. is attributable to high conversion6 and the presence
of hexane molecules in the crystal. The hexane
molecules possibly cause disorder of the lattice by
thermal motion. Based on the structure of the open-
ring isomers in the crystal, the main product is ascribed
to (S,S,S)-1b. The direction of the cyclization reaction
was regulated by the crystal lattice.
Very thin white needles of (S)-1a were obtained from
hexane. The absolute crystal structure was determined
by X-ray crystallography and the crystal packing is
shown in Fig. 2.10 (S)-1a adopted monoclinic chiral
space group P21. The distance between reactive carbons
,
is 3.46 A, which is short enough for the cyclization
reaction to take place in the crystalline phase. The
conformation of the open-ring isomer is restricted to M
in the hexatriene moiety. The distance between oxygen
of CO group and nitrogen of2 NH group is short
,
enough (2.78 A) to form hydrogen bonds. The hydro-
gen bonds control the crystal packing and conforma-
Figure 1. Absorption spectra of (S)-1a in hexane (1.9×10−5
M): open-ring form (solid-line), closed-ring form (dotted-line)
and in the photostationary state (313 nm) (dashed-line).
Figure 2. Crystal packing of (S)-1a. Hydrogen atoms are
omitted for clarity. (a) Top view (along the b axis). (b) Side
view.

K. Matsuda et al. / Tetrahedron Letters 42 (2001) 7291–7293
7293
References
1. (a) Irie, M., Ed. Chem. Rev. 2000, 100 (5), thematic issue
on Photochromism: Memories and Switches; (b) Du¨rr, H.;
Bouas-Laurent, H. Photochromism: Molecules and Sys-
tems; Elsevier: Amsterdam, 1990; (c) Brown, G. H. Pho-
tochromism; Wiley-Interscience: New York, 1971.
2. (a) Feringa, B. L.; Huck, N. P. M.; Schoevaars, A. M.
Adv. Mater. 1996, 8, 681–684; (b) Feringa, B. L.; Huck,
N. P. M.; van Doren, H. A. J. Am. Chem. Soc. 1995, 117,
9929–9930; (c) Yokoyama, Y.; Uchida, S.; Yokoyama,
Y.; Sugawara, Y.; Kurita, Y. J. Am. Chem. Soc. 1996,
118, 3100–3107; (d) Uchida, K.; Kawai, Y.; Shimizu, Y.;
Volkmar, V.; Irie, M. Chem. Lett. 2000, 654–655; (e)
Yamaguchi, T.; Inagawa, T.; Nakazumi, H.; Irie, S.; Irie,
M. Chem. Mater. 2000, 12, 869–871.
Figure 3. CD spectra of (S,S,S)-1b, (S,R,R)-1b, and (S)-1a
measured in hexane.
3. (a) Irie, M. Chem. Rev. 2000, 100, 1685–1716; (b) Irie,
M.; Uchida, K. Bull. Chem. Soc. Jpn. 1998, 71, 985–996.
4. (a) Yamaguchi, T.; Uchida, K.; Irie, M. J. Am. Chem.
Soc. 1997, 119, 6066–6071; (b) Murguly, E.; Norsten, T.
B.; Branda, N. R. Angew. Chem., Int. Ed. 2001, 40,
1752–1755.
5. (a) Irie, M.; Uchida, K.; Eriguchi, T.; Tsuzuki, H. Chem.
Lett. 1995, 890–899; (b) Kobatake, S.; Yamada, T.;
Uchida, K.; Kato, N.; Irie, M. J. Am. Chem. Soc. 1999,
121, 2380–2386; (c) Kobatake, S.; Yamada, M.; Yamada,
T.; Irie, M. J. Am. Chem. Soc. 1999, 121, 8450–8456; (d)
Yamada, T.; Kobatake, S.; Muto, K.; Irie, M. J. Am.
Chem. Soc. 2000, 122, 1589–1592; (e) Yamada, T.;
Kobatake, S.; Irie, M. Bull. Chem. Soc. Jpn. 2000, 73,
2179–2184.
CD spectra of the two diastereomers were measured.
Fig. 3 shows the CD spectra of the open-ring isomer
(S)-1a and the closed-ring isomer (S,S,S)-1b, (S,R,R)-
1b. The absolute structure was estimated from the
X-ray crystallographic structure of the open-ring iso-
mer. The open-ring isomer has a small Cotton effect at
310 nm, which is from the phenylethylamide side chain.
The closed-ring isomer has Cotton effect at 270, 310,
380, and 620 nm. The CD signal of the closed-ring
isomers was much larger than that of the open-ring
isomer. The signals of the two closed-ring isomers are
mirror images except the signal contribution from the
side chain. This result indicates that the CD signal of
the closed-ring isomer mainly originates from
the diarylethene moiety. Yokoyama et al. reported the
CD spectra of the closed-ring isomers of 1,2-bis(5-hy-
droxymethyl-2-methyl-3-thienyl)hexafluorocyclopentene
whose absolute structure is known.11 The sign of the
Cotton effect in the visible region was opposite to that
observed for 1b, though the band around 380 nm had
the same sign. 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 differ-
ence is considered to affect the sign of the Cotton
effect.
6. (a) Kodani, T.; Matsuda, K.; Yamada, T.; Irie, M. Chem.
Lett. 1999, 1003–1004; (b) Kodani, T.; Matsuda, K.;
Yamada, T.; Kobatake, S.; Irie, M. J. Am. Chem. Soc.
2000, 122, 9631–9637.
7. Irie, M.; Lifka, T.; Kobatake, S.; Kato, N. J. Am. Chem.
Soc. 2000, 122, 4871–4876.
8. Selected data for (S)-1a: white needles; 1H NMR (CDCl3,
200 MHz): l 1.43 (d, J=2.5 Hz, 3H), 1.97 (s, 3H), 1.99
(s, 3H), 5.35 (quintet, J=7 Hz, 1H), 6.33 (d, J=8 Hz
1H), 7.26–7.81 (m, 16H); UV–vis (hexane) umax (m) 300
(3.9×104); MS m/z (M+) 667. Anal. found: C, 64.87; H,
4.19; N, 2.16%. Calcd for C36H27F6NOS2: C, 64.75; H,
4.08; N. 2.10%.
9. Selected data for (1:1 mixture of (S,S,S)-1b and (S,R,R)-
1b): 1H NMR (CDCl3, 400 MHz): l 1.64 (d, J=7 Hz,
3H), 2.19 (s, 6H), 5.35 (quintet, J=7 Hz, 1H), 6.34 (d,
J=8 Hz 1H), 6.69 (s, 1H), 6.72 (s, 1H), 7.26–7.81 (m,
14H); UV–vis (hexane) umax (m) 371 (1.1×104), 383 (1.1×
104), 582 (1.8×104).
In conclusion, a diastereoselective photocyclization
reaction was observed in the single crystal of
diarylethene (S)-1a. This reaction was regulated by the
crystal lattice; CD spectra of the open-ring isomer and
the both diastereomers of the closed-ring isomers were
measured.
10. Crystallographic data for (S)-1a: Monoclinic space group
P21, a=18.2145(15), b=9.6866(8), c=23.834(2), i=
106.210(2), V=4038.0(6), Z=4, R (I>4|)=0.1044, wR2
(all data)=0.2905, =−0.02(17).
Acknowledgements
11. Yokoyama, Y.; Hosoda, N.; Osano, Y. T.; Sasaki, C.
Chem. Lett. 1998, 1093–1094.
This work was supported by CREST of Japan Science
and Technology Corporation.