Solid-state photoreaction in two-component molecular crystals of thienylacetic acids and aza aromatic compounds

Article abstract of DOI:10.1016/S0040-4020(00)00506-8

A series of two-component molecular crystals of 2-thienylacetic acid (1) or bis(2-thienyl)acetic acid (2) with aza aromatic compounds such as acridine (a) and phenanthridine (b) were prepared by crystallization from the solutions of both components. Irradiation of the crystals caused photodecarboxylation and radical intermediates which give decarboxylated and condensation products. The relationship between the crystal structures and the reaction paths are discussed. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0040-4020(00)00506-8

TETRAHEDRON
Pergamon
Tetrahedron 56 (2000) 6845±6852
Solid-State Photoreaction in Two-Component Molecular Crystals
of Thienylacetic Acids and Aza Aromatic Compounds
*
Hideko Koshima, Daisuke Matsushige, Masashi Miyauchi and Junko Fujita
Department of Applied Chemistry, Faculty of Engineering, Ehime University, Matsuyama 790-8577, Japan
Received 11 January 2000; accepted 10 April 2000
AbstractÐA series of two-component molecular crystals of 2-thienylacetic acid (1) or bis(2-thienyl)acetic acid (2) with aza aromatic
compounds such as acridine (a) and phenanthridine (b) were prepared by crystallization from the solutions of both components. Irradiation of
the crystals caused photodecarboxylation and radical intermediates which give decarboxylated and condensation products. The relationship
between the crystal structures and the reaction paths are discussed. q 2000 Elsevier Science Ltd. All rights reserved.
Introduction
type of PET reaction for the two-component crystals formed
from carboxylic acids and electron acceptors, and found that
the solid-state photodecarboxylation usually occurred with a
remarkable selectivity compared with the solution phase
photodecarboxylation. These reactions comprise stoichio-
metrically sensitized decarboxylation in the two-component
crystals of various aralkyl carboxylic acids and aza aromatic
compounds;9 photodecarboxylation and decarboxylative
condensation in the CT crystals of arylacetic acids and
1,2,4,5-tetracyanobenzene through excitation of the CT
bands;10 photodecarboxylation in the two-component
Solid-state photoreactions have attracted much attention
from a number of organic chemists.1±3 A large number of
photoinduced electron transfer (PET) reactions are known
in the solution phase.4 We have developed solid-state
bimolecular photoreactions utilizing PET in two-component
molecular crystals in which the electron donor and electron
acceptor species were combined.5±7 It is well known that
carboxylic acids undergo PET followed by decarboxylation
when various electron acceptors are used.8 We utilized this
Chart 1.
Keywords: solid state bimolecular photoreactions; photodecarboxylation; two-component molecular crystals; thienylacetic acids, aza aromatic compounds.
* Corresponding author. Tel.: 181-89-927-8523; fax: 181-89-927-9923; e-mail: koshima@en3.ehime-u.ac.jp
0040±4020/00/$ - see front matter q 2000 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(00)00506-8

6846
H. Koshima et al. / Tetrahedron 56 (2000) 6845±6852
Table 1. Crystal data of the two-component crystals
1´a
2´a
2´b
Crystal data
Formula
C19H15NO2S
321.39
Triclinic
C33H25NO4S4
627.80
Triclinic
C23H17NO2S2
403.51
Triclinic
Mw
Crystal system
Space group
ꢀ
ꢀ
ꢀ
P1
P1
P1
Ê
a (A)
10.190(1)
10.646(2)
7.7448(2)
95.28(2)
98.65(2)
106.27(1)
789.3(3)
2
10.037(2)
13.309(3)
6.051(2)
99.22(2)
106.98(2)
79.91(2)
756.0(4)
1
9.815(2)
13.608(3)
8.430(1)
99.79(1)
104.62(2)
106.58(2)
1008.0(4)
2
Ê
b (A)
Ê
c (A)
a (8)
b (8)
g (8)
Ê 3
V (A )
Z
Dc (g cm23
F(000)
)
1.352
336.00
2.14
1.379
326.00
3.54
1.329
420.99
2.70
m (cm23
)
Data collection
Crystal size (mm)
2umax (8)
No. of re¯ections measured
0.2£0.3£0.5
55.0
3831
0.4£0.3£0.5
50.0
2823
0.3£0.4£0.6
50.0
3765
Final re®nement
No. of observations, I.3s(I)
No. of variables
2721
186
1441
161
2348
257
R
Rw
0.077
0.128
0.086
0.118
0.055
0.080
crystals of N-phenylglycine and aza aromatic compounds;11
enantioselective photodecarboxylative condensation in
chiral crystals;12,13 and absolute asymmetric synthesis by
photodecarboxylative condensation within the chiral two-
component crystal formed from diphenylacetic acid and
acridine.14
Fig. 1 shows the molecular arrangement of 1´a. The
molecule of 1 is connected to a through O±H´´´N hydrogen
Ê
bonding with an H1±N1 distance of 1.74 A (Fig. 1b). The
two antipodal molecular pairs are arranged centrosym-
Å
metrically in the unit cell (P1, Zˆ2) (Fig. 1a). Further,
these pairs are stacked in a head-to-tail manner to form a
columnar structure along the c-axis (Fig. 1b). The acridine
molecules are almost parallel with a plane-to-plane
This paper describes the preparation of a series of thienyl-
acetic acids and aza aromatic compounds and their solid-
state and solution photoreactions.
Ê
distance of 4.0 A. Here the thiophene ring of molecule 1
is disordered, with S and C atoms coexisting at 75 and 25%
occupancies, respectively.
The crystal 2´a (Fig. 2) has a very different packing arrange-
ment. The two molecules of 2 form a carboxy dimer in the
lattice (Fig. 2a). Further, an acridine molecule is surrounded
by two carboxy dimers to form an inclusion complex on the
ab face. One of thiophene rings of molecule 2 is disordered,
with S and C atoms coexisting at 60 and 40% occupancies,
respectively (Fig. 2b). The acridine molecule is also
disordered with the coexistence of N and C atoms at 50%
occupancy. The position of the carboxy hydrogen atom
could not be determined probably due to disorder.
Results and Discussion
Two-component molecular crystals
2-Thienylacetic acid (1) and bis(2-thienyl)acetic acid (2)
were chosen as carboxylic acids and acridine (a), phenan-
thridine (b), benzo[f]quinoline (c), phenazine (d), quinoline
(e), 3-bromoquinoline (f), and 4,40-bipyridine (g) as aza
aromatic compounds (Chart 1). Ten two-component
molecular crystals were prepared by crystallization from
the solutions of both components. The molar ratios of the
acid and aza aromatic compounds are 1:1 for 1´a, 2´b, 2´c,
2´e and 2´f, 2:1 for 1´d, 1´g, 2´a and 2´g, and 2:3 for 2´d. The
solvents, melting points and IR spectra are summarized in
the Experimental section. The solid-state CD spectra of the
crystals were measured as Nujol mulls to determine whether
the crystals are chiral or not.15,16 However, no signi®cant
solid-state CD spectra were observed for any of the 10
crystals, suggesting that these crystals are most probably
achiral. Three crystals 1´a, 2´a and 2´b were submitted to
X-ray crystallographic analysis to con®rm their achiral
The crystal 2´b (Fig. 3) has a similar molecular arrangement
to that of 1´a. The molecule of 2 is connected to b through
O±H´´´N hydrogen bonding with an H1±N1 distance of
Ê
1.73 A (Fig. 3b). The two antipodal pairs are arranged
Å
centrosymmetrically in the unit cell (P1, Zˆ2) (Fig. 3a).
Further, the pairs are stacked in a head-to-tail manner to
form a columnar structure along the c-axis (Fig. 3b). The
phenanthridine molecules are almost parallel with a plane-
Ê
to-plane distance of 3.6 A.
Solution and solid-state photoreactions
Å
nature, and all were found to belong to space group P1.
The details of the crystal data are listed in Table 1.
Herein photoreactions of 1 with a, and 2 with a or b were

H. Koshima et al. / Tetrahedron 56 (2000) 6845±6852
6847
Figure 1. (a) Molecular arrangement and (b) reaction path in the crystal 1´a. In (b), crossed atoms in the disordered thiophene represent the coexistence of S
and C atoms with occupancies of 75 and 25%, respectively; conversely dotted atoms, 25 and 75%.
examined. Irradiation of 1 and a in acetonitrile under argon
resulted in decarboxylation followed by radical coupling to
give condensation product 3 and biacridane (4) as the main
products with low product selectivities (Scheme 1 and Table
2, entry 5). The solid-state photoreaction of crystalline 1´a at
158C afforded the same products 3 and 4 as those from the
solution reaction (entries 1 and 2). However, irradiation at
2308C gave 3 alone in low yields (entries 3 and 4). The poor
material balance may be due to vaporization of the possible
decarboxylated product 2-methylthiophene during irradia-
tion as discussed below.
tively (Scheme 2 and Table 3, entries 10 and 11). In contrast
to the high conversion of a (92%), b was consumed only
slightly (14%).
On the other hand, irradiation of the crystal 2´a gave bis(2-
thienyl)methane (5) as the decarboxylated product, and 6 as
the condensation product (Table 3, entries 1±3). Here, the
product 5 is different from the decarboxylated dimer 7
produced by the solution reaction. However, at the initial
reaction stage, 5 alone was selectively obtained on irradia-
tion at 210 and 2308C (entries 4 and 5). The low yields of 5
suggest the occurrence of side reactions. The reaction was
brought about by irradiation using visible light (.400 nm)
(entry 3). Therefore, this reaction can be induced by the
excitation of the acridine molecule a at .400 nm, and a
acts as the excited species in the crystal 2´a.
Irradiation of 2 and the aza aromatic compound a or b in
acetonitrile caused similar decarboxylation to give 1,1,2,2-
tetrakis(2-thienyl)ethane (7) as the decarboxylated dimer
and the corresponding condensation product 6 or 8, respec-

6848
H. Koshima et al. / Tetrahedron 56 (2000) 6845±6852
Figure 2. (a) Molecular arrangement and (b) reaction path in the crystal 2´a. In (b), crossed atoms in the disordered thiophene represent the coexistence of S
and C atoms with occupancies of 60 and 40%, respectively; conversely dotted atoms, 40 and 60%. Black atoms in the disordered acridine represent the
coexistence of N and C atoms with occupancies of 50%.
Solid-state photoreaction of the crystal 2´b gave 5 and 8,
similarly to those of 2´a (entries 6 and 7). Only 5 was selec-
tively obtained at the initial reaction stage of the irradiation
under cooling (entries 8 and 9).
Although these reaction processes inevitably lead to
alteration of the crystal lattice, the reaction paths at the
initial reaction stage can be discussed on the basis of the
distances estimated from the crystallographic data. In the
crystal 1´a (Fig. 1b), hydrogen abstraction should be a
higher priority than radical coupling because of the shorter
C1±H1 distance (3.18 A) for hydrogen abstraction than
the C1±C2 or C1±C3 radical coupling distances of 5.18
Ê
or 5.72 A, respectively. Probably the reason why
2-methylthiophene (derived from hydrogen abstraction)
was not obtained is its vaporization during the irradiation
(Table 2, entries 3 and 4). The relatively high yields of
radical coupling products 3 and 4 can be explained by the
considerable decomposition of the initial crystal structure of
1´a at the high conversions (100 and 65%) of 1 and a,
respectively (entry 2).
Scheme 3 shows the possible reaction mechanism. Irradia-
tion of the crystal causes electron transfer from the acid to
the aza aromatic compound followed by proton transfer, or
conversely proton transfer followed by electron transfer, to
afford carboxylate radical (9), and hydroacridine radical
(10) or hydrophenanthridine radical (11). Next, decarboxy-
lation of 9 produces the radical (12). Hydrogen abstraction
can occur from the N±H of 10 or 11 by the active radical 12
leading to the formation of 5 in the crystals 2´a and 2´b, as
opposed to the radical coupling of 12 to give 7 in solution.
Radical coupling between 12 and 10, or 12 and 11 occurs to
give 3, 6 or 8. In the crystal 1´a, radical coupling of 10 also
can occur to produce the dimer 4.
Ê
The crystal 2´a has an inclusion complex structure (Fig. 2).
Scheme 1.

H. Koshima et al. / Tetrahedron 56 (2000) 6845±6852
6849
Figure 3. (a) Molecular arrangement and (b) reaction path in the crystal 2´b.
The two molecules of 2 should form a carboxy dimer from
the O1´´´O20 distance of 3.10 A and also hydrogen
Ê
bonding to the acridine molecule from the O1´´´N(C2)
Ê
distance of 2.97 A (Fig. 2b). Here the N atom is dis-
ordered, with the N and C atoms coexisting at 50%
occupancies. The active radical 12 abstracts the carboxy
hydrogen to give 5 alone at the initial reaction stage,
but the distance for hydrogen abstraction is not known
because the position of the carboxy hydrogen atom
could not be found in the crystal data analysis. Radical
Table 2. Photoreaction of 2-thienylacetic acid and acridine in crystalline
state and in solution
Ê
coupling with the C1±C2 radical distance (4.98 A)
gives 6.
Entry
Irradiation
Conversion (%)
Corrected yield (%)
(8C) Lamp (h)
1
a
3
4
In the case of crystal 2´b (Fig. 3b), hydrogen abstraction by
the radical 12 occurs across the shortest C1±H1 distance
Solid state
Ê
(3.14 A) at the initial reaction stage under cooling (Table
1
2
3
4
15 Hg
0.1
0.5
2
83
100
33
18
65
3
23
52
12
8
30
48
±
15 Hg
230 Xe
230 Xe
3, entries 8 and 9). Radical coupling also occurs upon irra-
diation at 158C between a neighboring radical pair 12 and
11, which is derived from a hydrogen bonding pair with the
5
51
4
±
MeCN soln.
rt
Ê
C1±C2 distance (5.27 A) in the starting crystal (entries 6
and 7).
5
Hg
4
81
100
44
45

6850
H. Koshima et al. / Tetrahedron 56 (2000) 6845±6852
Scheme 2.
Table 3. Photoreaction of bis(2-thienyl)acetic acid and aza aromatic compounds in solid state and in solution
Entry
Components
Irradiation
Lamp
Conversion (%)
Corrected yield (%)
(8C)
(h)
2
a or b
5
7
6
8
Solid state
1
2
3
4
5
6
7
8
9
2´a
2´a
2´a
2´a
2´a
2´b
2´b
2´b
2´b
15
15
15
210
230
15
15
210
230
Hg
Xe
0.5
1
1
1
4
0.5
1
1
96
74
62
26
15
100
37
10
7
92
12
12
7
25
24
27
30
39
63
59
72
56
76
63
75
±
Xe (.400 nm)
Xe
Xe
Hg
Xe
Xe
Xe
5
±
23
12
11
4
40
23
±
1
±
MeCN soln.
10
11
21a
21b
rt
rt
Hg
Hg
5
9
100
89
92
14
13
49
65
50
Scheme 3.

H. Koshima et al. / Tetrahedron 56 (2000) 6845±6852
6851
Experimental
7.13 (m, 3H), 6.97 (dd, Jˆ7.5, 1.2 Hz, 2H), 6.80±8.86 (m,
3H), 6.71 (dd, Jˆ7.5, 1.2 Hz, 2H), 6.35 (d, Jˆ2.7 Hz, 1H),
6.01 (s, 1H), 4.22 (t, Jˆ6.9 Hz, 1H), 3.05 (d, Jˆ6.9 Hz, 2H);
IR (KBr) 3375 cm21. Anal. Calcd for C18H15NS: C, 77.94;
H, 5.45; N, 5.05. Found: C, 77.87; H, 5.53; N, 4.95.
General procedures
1H-NMR spectra were measured on a JEOL JNM-GSX270
spectrometer with tetramethylsilane as an internal standard.
IR spectra were recorded on a Horiba FT/IR-210 spectro-
photometer. Melting points were not corrected. Elemental
analysis was carried out with a Yanaco CHN Corder MT-5.
HPLC with a photodiode-array detector were used for
determining the products on a Waters HPLC system.
4: mp 211±2128C (from THF). The IR spectrum and
elemental analysis of 4 were consistent with those of the
authentic sample.7
Irradiation of 2 (1121 mg) and a (895 mg) in MeCN for 5 h
gave 6 (1303 mg) and 7 (268 mg) in 65 and 13% yields,
respectively.
Preparation of two-component molecular crystals
1
6: mp 206±2088C (from MeCN); H NMR (DMSO-d6) d
The two-component molecular crystals investigated here
incorporate 2-thienylacetic acid (1) and bis(2-thienyl)acetic
acid (2) as the acid components and aza aromatic
compounds such as acridine (a), phenanthridine (b),
benzo[f]quinoline (c), phenazine (d), quinoline (e),
3-bromoquinoline (f), and 4,40-bipyridine (g) as electron
acceptors (Chart 1). The starting acid compound 2 was
synthesized by condensation of chloral and thiophene
followed by alkaline treatment.17,18 Ten two-component
molecular crystals were prepared by crystallization from
the solutions of both components:
9.15 (s, 1H); 6.82±6.85 (m, 4H), 6.73 (s, 2H), 6.70 (s, 4H),
6.49±6.58 (m, 4H), 4.55 (d, Jˆ8.4 Hz, 1H), 4.39 (d,
Jˆ8.4 Hz, 1H); IR (KBr) 3373 cm21. Anal. Calcd for
C22H17NS2: C, 73.49; H, 4.77; N, 3.90. Found: C, 73.55;
H, 4.82; N, 4.08.
7: mp 161±1648C (from MeCN); 1H NMR (CDCl3) d 7.08±
7.10 (m, 4H), 6.78±6.82 (m, 8H), 5.14 (d, Jˆ10.5 Hz, 2H);
IR (KBr) no NH. Anal. Calcd for C18H14S4: C, 60.29; H,
3.94. Found: C, 60.23; H, 3.94.
Irradiation of 2 (1121 mg) and b (895 mg) in MeCN for 9 h
gave 7 (520 mg) and 8 (145 mg) in 26 and 7% yields,
respectively.
1´a: yellow prisms; 1:1; mp 68±718C (from MeCN); IR
;
(KBr) 3057, 1697 cm21
1´d: yellow needles; 2:1; mp 71±738C (from MeCN); IR
(KBr) 1716 cm21
1´g: brown prisms; 2:1; mp 75±788C (from MeCN); IR
(KBr) 3091, 1691 cm21
2´a: brown prisms; 2:1; mp 80±838C (from AcOEt); IR
(KBr) 3088, 1701 cm21
2´b: brown prisms; 1:1; mp 67±688C (from AcOEt); IR
(KBr) 3103, 1718 cm21
2´c: brown prisms; 1:1; mp 85±888C (from AcOEt); IR
(KBr) 3101, 1713 cm21
2´d: yellow needles; 2:3; mp 112±1168C (from MeCN);
IR (KBr) 3093, 1705 cm21
2´e: brown prisms; 1:1; mp 73±768C (from AcOEt); IR
(KBr) 3097, 1709 cm21
2´f: brown prisms; 1:1; mp 66±688C (from AcOEt); IR
(KBr) 3107, 1720 cm21
2´g: brown prisms; 2:1; mp 93±958C (from MeCN); IR
(KBr) 3105, 1701 cm21
;
1
8: mp 206±2088C (from MeCN); H NMR (DMSO-d6) d
8.12 (d, Jˆ7.5 Hz, 4H), 7.97 (d, Jˆ7.5 Hz, 4H), 7.76±7.85
(m, 6H), 6.45 (d, Jˆ7.5 Hz, 1H), 6.30 (d, Jˆ7.5 Hz, 1H),
5.57 (s, 1H); IR (KBr) 3375 cm21. Anal. Calcd for
C22H17NS2: C, 73.49; H, 4.77; N, 3.90. Found: C, 73.77;
H, 4.91; N, 4.12.
;
;
;
Solid-state photoreaction
;
A crystal (20 mg) was pulverized in a mortar, placed
between two Pyrex glass plates, and irradiated under
;
argon with
a 400-W high-pressure mercury lamp
;
(.290 nm irradiation), or a 500-W xenon short arc lamp
with a UV cut ®lter (.400 nm irradiation) or without ®lter
(.290 nm irradiation). The irradiated sample was ®ltered
and the solution was treated with CH2N2 followed by HPLC
analysis. The results are shown in Schemes 1 and 2, and
Tables 2 and 3.
;
.
Preparative photoreaction in solutions
X-Ray crystallographic analysis
Common procedure: a solution (100 ml) of a thienylacetic
acid (5 mmol) and an aza aromatic compound (5 mmol) was
internally irradiated with a 100-W high-pressure mercury
lamp under argon bubbling at room temperature. The reac-
tion mixture was ®ltered to separate a precipitate of 4, 6 or 8
and then the solution was submitted to preparative TLC
(silica gel plate).
Three crystals of 1´a, 2´a and 2´b were submitted to X-ray
structure analysis. Data collections were performed on a
Rigaku AFC5R automatic four-circle X-ray diffractometer
Ê
with a graphite-monochromated Mo Ka (lˆ0.71069 A)
radiation. Absorption corrections were applied. No degrada-
tion of the crystal by X-ray was ascertained in all cases by
repeated monitoring of the three representative re¯ections
every 150 re¯ections. These structures were solved by direct
methods and expanded using Fourier techniques. The non-
hydrogen atoms were re®ned anisotropically. Atomic para-
meters were re®ned by the full-matrix least-squares method
at the ®nal stage. All the calculations were carried out on
Irradiation of 1 (711 mg) and a (895 mg) in MeCN for 4 h
gave 3 (604 mg) and 4 (420 mg) in 44 and 47% yields,
respectively.
3: mp 195±1968C (from MeCN); 1H NMR (CDCl3) d 7.07±

6852
H. Koshima et al. / Tetrahedron 56 (2000) 6845±6852
Lett. 1989, 30, 6733±6736. (e) Okada, K.; Okubo, K.; Oda, M.
J. Photochem. Photobiol. A: Chem. 1991, 57, 265±277.
(f) Tsujimoto, K.; Nakao, N.; Ohashi, M. J. Chem. Soc., Chem.
Commun. 1992, 366±367.
teXsan crystallographic software package, Molecular Struc-
ture Corporation. The crystal data are listed in Table 1.
Acknowledgements
9. (a) Koshima, H.; Ding, K.; Matsuura, T. J. Chem. Soc., Chem.
Commun. 1994, 2053±2054. (b) Koshima, H.; Ding, K.; Chisaka,
Y.; Matsuura, T.; Miyahara, I.; Hirotsu, K. J. Am. Chem. Soc. 1997,
119, 10317±10324.
This work was supported by grants from the Ministry of
Education, Science, Sports, and Culture, Japan (Scienti®c
Research A, No. 11304051), and the Yamada Science
Foundation in Japan.
10. Koshima, H.; Ding, K.; Chisaka, Y.; Matsuura, T.; Ohashi, Y.;
Mukasa, M. J. Org. Chem. 1996, 61, 2352±2357.
11. Koshima, H.; Ding, K.; Miura, T.; Matsuura, T. J. Photochem.
Photobiol. A: Chem. 1997, 104, 105±112.
References
12. Koshima, H.; Ding, K.; Chisaka, Y.; Matsuura, T. Tetrahedron:
Asymmetry 1995, 6, 101±104.
1. (a) Cohen, M. D.; Schmidt, G. M. J. Chem. Soc. 1964, 1996±
2000. (b) Schmidt, G. M. J. Pure Appl. Chem. 1971, 27, 647±678.
2. Scheffer, J. R.; Garcia-Garibay, M. Photochemistry in Solid
Surfaces; Anpo, M., Matsuura, T. Eds.; Elsevier: Amsterdam,
1989, pp 501±525.
13. Koshima, H.; Nakagawa, T.; Matsuura, T. Tetrahedron Lett.
1997, 38, 6063±6066.
14. Koshima, H.; Ding, K.; Chisaka, Y.; Matsuura, T. J. Am.
Chem. Soc. 1996, 118, 12059±12065.
15. (a) Toda, F.; Miyamoto, H.; Kanemoto, K. J. Org. Chem.
1996, 61, 6490±6491. (b) Toda, F.; Miyamoto, H.; Kikuchi, S.;
Kuroda, R.; Nagami, F. J. Am. Chem. Soc. 1996, 118, 11315±
11316.
3. Reactivity in Molecular Crystals, Ohashi, Y. Ed.; VCH:
Weinheim, 1993.
4. Photoinduced Electron Transfer; Part C, Fox, M. A., Chanon,
M. Eds.; Elsevier: Amsterdam, 1988.
16. (a) Koshima, H.; Nakagawa, T.; Matsuura, T.; Miyamoto, H.;
Toda, F. J. Org. Chem. 1996, 62, 6322±6325. (b) Koshima, H.;
Hayashi, E.; Matsuura, T.; Tanaka, K.; Toda, F.; Kato, M.;
Kiguchi, M. Tetrahedron Lett. 1997, 38, 5009±5012. (c) Koshima,
H.; Khan, S. I.; Garcia-Garibay, M. A. Tetrahedron: Asymmetry
1998, 9, 1851±1854. (d) Koshima, H.; Honke, S.; Fujita, J. J. Org.
Chem. 1999, 64, 3916±3921.
5. Koshima, H.; Matsuura, T. Kokagaku 1995, 19, 10±20.
6. Koshima, H.; Matsuura, T. J. Photochem. Photobiol. A: Chem.
1996, 100, 85±91.
7. Koshima, H.; Wang, Y.; Matsuura, T.; Miyahara, I.; Mizutani,
H.; Hirotsu, K.; Asahi, T.; Masuhara, H. J. Chem. Soc., Perkin
Trans. 2 1997, 2033±2038.
8. (a) Noyori, R.; Kato, M.; Kawanishi, M.; Nozaki, H.
Tetrahedron 1969, 25, 1125±1136. (b) Brimage, D. R. G.;
Davidson, R. S.; Steiner, P. R. J. Chem. Soc., Perkin Trans. 1
1973, 526±529. (c) Libman, J. J. Am. Chem. Soc. 1975, 97,
4139±4141. (d) Okada, K.; Okubo, K.; Oda, M.; Tetrahedron
17. Freeman, J. F.; Dove, J. R.; Amstuts, E. D. J. Am. Chem. Soc.
1948, 70, 3137.
18. Schildknecht, E. A.; Brown, E. V. J. Am. Chem. Soc. 1955, 77,
954±957.