A novel photochemical reaction of 2-alkoxynicotinates to cage-type photodimers

Article abstract of DOI:10.1021/jo016315u

Irradiation of a benzene solution of 2-alkoxynicotinic acid alkyl esters gave cage-type photodimers in good yields, the structure of which was established by X-ray single-crystal analysis. The maximum quantum yield was 8.0 × 10^-2 when a 5.0 M (almost neat) solution was used. Photolysis of phenyl 2-methoxynicotinate promoted photo-Fries rearrangement to give 1,3- and 1,5-rearranged products. Excimer emission of methyl 2-methoxynicotinate was observed at 77 K.

Full text of DOI:10.1021/jo016315u

J . Org. Chem. 2002, 67, 1843-1847
1843
A Novel P h otoch em ica l Rea ction of 2-Alk oxyn icotin a tes to
Ca ge-Typ e P h otod im er s
Masami Sakamoto,* Tadao Yagi, Shohei Fujita, Takashi Mino, Takashi Karatsu, and
Tsutomu Fujita
Department of Materials Technology, Faculty of Engineering, Chiba University,
Yayoi-cho, Inage-ku, Chiba 263-8522, J apan
saka@tc.chiba-u.ac.jp
Received November 26, 2001
Irradiation of a benzene solution of 2-alkoxynicotinic acid alkyl esters gave cage-type photodimers
in good yields, the structure of which was established by X-ray single-crystal analysis. The maximum
-
2
quantum yield was 8.0 × 10 when a 5.0 M (almost neat) solution was used. Photolysis of phenyl
-methoxynicotinate promoted photo-Fries rearrangement to give 1,3- and 1,5-rearranged products.
Excimer emission of methyl 2-methoxynicotinate was observed at 77 K.
2
In tr od u ction
dimerization of nicotinic acid esters leading to cage-type
photodimers.
The photochemical reaction of aromatic compounds has
received much attention from both the mechanistic and
Resu lts a n d Discu ssion
synthetic perspectives,1
-5
and the intra- and inter-
molecular photochemical addition reactions of carbon
aromatics are well documented.6-11 Photochemical addi-
tion of benzene derivatives with alkenes is a useful
method for synthesizing natural products. Furthermore,
2-Alkoxynicotinates 1a -f were conveniently prepared
by alkoxylation and acid-catalyzed esterification from
2-chloronicotinic acid.1
5,16
Photochemical experiments
were carried out by irradiation of an argon-degassed
benzene solution at room temperature with a Pyrex-
filtered light from 1000-W high-pressure mercury lamp.
The consumption of the starting esters was checked by
TLC; irradiation time depended on the concentration of
the esters and needed 2-8 h. For example, when a
benzene solution containing 100 mg of methyl 2-meth-
oxyniconinate 1a (0.1 M) was irradiated for 2 h and the
crude photolyzate was subjected to chromatography on
silica gel, a dimer 2a , 5,11-dimethoxy-4,10-diazapenta-
4
π + 4π photodimerization of polycyclic aromatic sys-
tems, such as naphthalene and anthracene derivatives,
are investigated not only for the fundamental photo-
physical and photochemical properties but also for a wide
range of applications. However, in contrast, the dimer-
ization of monocyclic aromatics, benzene and its deriva-
tives, has not been successful in a photochemical reac-
tion12 because of the disadvantageously enormous loss
of aromatic energy of two aromatic molecules. We are
interested in new aspects of the photochemical cyclo-
addition of aromatic compounds and the application of
the methodology to heteroaromatics and have reported
cyclo[6.4.0.0.2 0.
,7
3,12 6,9
0 ]dodeca-4,10-diene-6,12-dicarbox-
ylic acid dimethyl ester, was isolated in 85% yield at 80%
conversion yield as shown in Table 1, entry 1. Photolysis
of other nicotinic acid esters 1b-d also gave the corre-
sponding dimers 2b-d in good yields (entries 2-4). The
dimerization was influenced by the substituent on the
6-position of the pyridine ring. For the photolysis of 1e,
the substitution of a methyl group at the 6-position
resulted in low reactivity for the photoreaction, and the
prolonged irradiation for 8 h gave an intractable mixture
a unique 2 + 2 photodimerization of 2-alkoxy-3-cyano-
pyridines.1
3,14
We have now found a new type of photo-
*
401.
To whom correspondence should be addressed. Fax: 81-43-290-
3
(
(
(
(
(
1) Bryce-Smith, D.; Gilbert, A. Tetrahedron 1976, 32, 1309.
2) McCullough, J . J . Chem. Rev. 1987, 87, 811.
3) Becker, H. D. Chem. Rev. 1993, 93, 145.
4) Sieburth, S. McN.; Cunard, N. T. Tetrahedron 1996, 52, 6251.
5) Bouras-Laurent, H.; Castellan, A.; Desvergne, J .-P.; Lapouyade,
(
Table 1, entry 5). The difference in reactivity might be
attributed to the steric effect of the methyl group.
However, phenol ester 1f showed completely different
photochemical behavior (Table 1, entry 6). When a 0.02
M benzene solution of 1f was irradiated, excitation of the
molecule led to the reaction at the ester functionality
instead of the pyridine ring, the photo-Fries rearrange-
ment proceeded, and 1,3- and 1,5-rearranged products
(3 and 3′) were obtained in 47% and 29% yield, respec-
R. Chem. Soc. Rev. 2000, 29, 43.
6) Bradshaw, J . S.; Hammond, G. S. J . Am. Chem. Soc. 1963, 85,
953.
(
3
3
9
(7) Teitei, T.; Wells, D.: Sasse, W. H. F. Tetrahedron Lett. 1974,
67.
(8) Seliger, B. K.; Sterns, M. J . Chem. Soc., Chem. Commun. 1969,
78.
(
(
(
(
9) Becker, H.-D. Adv. Photochem. 1990, 15, 139.
10) Kaupp, G.; Teufel, E. Chem. Ber. 1980, 113, 3669.
11) Becker, H.-D.; Langer, V. J . Org. Chem. 1993, 58, 4703.
12) Two benzene rings replaced closely in the rigid system under-
17,18
tively, as the only isolable products.
went photocycloaddition intramolecularly. Matohara, K.; Lim, C.;
Yasutake, M.; Nogita, R.; Koga, T.; Sakamoto, Y.; Shinmyozu, T.
Tetrahedron Lett. 2000, 41, 6803 and references therein.
(15) Hardegger, E.; Nickles, E. Helv. Chim. Acta 1956, 39, 505.
(16) Sliwa, H. Bull. Soc. Chim. Fr. 1970, 631.
(17) Several photo-Fries rearrangement of aryl esters have been
reported. Martinez-Utrilla, R.; Miranda, M. A. Tetrahedron Lett. 1980,
21, 2281.
(
13) Sakamoto, M.; Kimura, M.; Fujita, T.; Nishio, T.; Iida, I.,
Watanabe, S. J . Am. Chem. Soc. 1991, 113, 5859.
14) Sakamoto, M.; Tadao, Y.; Mino, T.; Yamaguchi, K.; Fujita, T.
J . Am. Chem. Soc. 2000, 122, 8141.
(
1
0.1021/jo016315u CCC: $22.00 © 2002 American Chemical Society
Published on Web 02/23/2002

1
844 J . Org. Chem., Vol. 67, No. 6, 2002
Sakamoto et al.
Ta ble 1. P h otoch em ica l Rea ction of 2-Alk oxyn icotin a tes
a -f in Ben zen e
1
yields (%)b
conv (%) of 2 or (3, 3′)c
entry
ester 1a
R1
R2
R3
1
2
3
4
5
6
1a
1b
1c
1d
1e
Me
Me
Et
Me
Me
Me
Me
Et
Me
Pri
Me
Ph
H
H
H
H
Me
H
80
68
56
51
48
45
85
89
93
87
0
d
e
0 (47, 29)c
1f
F igu r e 1. (a) Fluorescence spectrum of 1a at the concentra-
-
3
a
A benzene solution (0.1 M) was irradiated for 2 h. b The
tion of 1.0 × 10 in EPA (ethanol/isopentane/ether 2:5:5) at
chemical yields were determined on the basis of consumed
nicotinates 1. Number in parentheses is the yield of photo-Fries
rearrangement products 3 (1,3-rearrangement) and 3′ (1,5-re-
arrangement). Intractable mixture was formed after 8 h of
room temperature, excitation at 290 nm, band-pass 3 nm. (b)
c
-3
Fluorescence spectrum of 1a at the concentration of 1.0 × 10
in EPA at 77 K, excitation at 290 nm, band-pass 1.5 nm.
d
e
irradiation. Benzene solution (0.02 M) was irradiated for 0.5 h.
stable at room temperature for several weeks. However,
when 2a was heated in refluxing toluene for 1 h or the
acetonitrile solution was irradiated with short wave-
length light (254 nm), the starting nicotinic acid ester
1a was obtained quantitatively.
Ta ble 2. Qu a n tu m Yield s for Dim er iza tion of 1a
solvent
concn (mol/L)
Φdim. (× 10-3)
benzene
benzene
benzene
benzene
MeCN
0.01
0.1
1.0
5.0
0.1
0.1
0.1
0.3
1.6
13
The intermolecular photoreaction should be influenced
by the concentration of the substrate. Table 2 shows the
quantum efficiency for the formation of 2a under various
concentrations. When a benzene solution of 2a at a
concentration under 0.01 M was used, the cycloaddition
80
1.8
1.6
2.2
C6H12
EtOH
-3
was quite inefficient (Φ ) 3 × 10 ). The value increased
The dimer structure 2a -d was determined on the basis
of the spectral data. The structural analysis was exem-
plified by 2a ; the HR-Mass (FAB) spectrum showed a
molecular ion peak at 335.1211 (M + 1), which strongly
suggested the dimeric structure. The H NMR spectrum
showed the methine protons at δ 2.89 (dt, J ) 7.8 and
.1 Hz, 2H, 2- and 8-H), 3.29 (t, J ) 7.1 Hz, 2H, 1- and
-H), and 5.23 (d, J ) 7.8 Hz, 2H, 3- and 9-H) derived
from cyclobutane substructure. The C NMR spectrum
exhibited peaks at δ 27.1 (d, 2- and 8-C), 35.1 (d, 1- and
-C), 55.6 (s, 6-, 12-C), and 57.7 (d, 3- and 9-C) derived
according to the concentration linearly and was 1.6 ×
-
3
-2
10 and 1.3 × 10 , at 0.1 and 1.0 M of concentration,
respectively. The maximum quantum yield was 8.0 ×
-
2
10
when 5.0 M (almost neat) solution was used.
1
Furthermore, it seems that a protic solvent is somewhat
preferred for the dimerization; however, considerable
differences have not been observed. In the case of 1f,
irradiation of a higher concentrated benzene solution (0.5
M) did not give the corresponding dimers but also gave
1,3- and 1,5-rearrangement products, 3 and 3′, in 48%
and 39% yield, respectively, when the conversion yield
reached at 23%.
The photochemical cycloadditions of many aromatic
compounds proceed via a singlet excimer or exciplex. In
the fluorescence spectra of 1a at room temperature
(Figure 1(a)), only strong emission derived from an
excited monomer was observed at 326 nm without any
new emissions. On the other hand, when the fluorescence
was measured at 77 K, a new emission assignable to that
from the excimer was observed at 430 nm accompanied
with fluorescence from the monomer (Figure 1(b)). It
seems that dimerization could be faster than emission
from the excimer at room temperature. Quenching of the
7
7
1
3
7
from cyclobutane sp carbons, in addition to the sp2
carbon peaks at 164.2 (s, CdN) and 172.3 (s, CdO). The
assignment was made using the COSY sequence. These
spectral data strongly supported the C-2 symmetrical
structure of cage-type photodimer 2a .
Finally, the cage structure of 2a was established by
X-ray crystallographic analysis.19 The four-membered
rings show a range of bond lengths from 1.522(3) to
3
1
.592(3) Å and bond angles of 88.6-90.6°. Despite pos-
sessing three fused cyclobutane rings, the dimers were
(18) Photo-Fries rearrangement of nicotinate derivative have been
reported. Beelitz, K.; Praefcke, K. Liebiegs Ann. Chim. 1979, 1081.
dimerization by 0.02 M of 2,5-dimethylhexa-2,4-diene (E
T
(
19) The dimer 2a gave prismatic crystals of monoclinic space group
-
1
P2
9
1
/c (No. 14), a ) 12.661(4) Å, b ) 7.399(1) Å, c ) 16.810(10) Å, â )
58.7 kcal mol ) was quite inefficient, whereas pyridine
3
-3
2.08(3)°, V ) 1573(1) Å , Z ) 4, F ) 1.411 gcm , µ(Cu KR) ) 1.09
-1 20
has triplet energy at 84.7 kcal mol
.
This fact also
-
1
cm , F(000) ) 704.00. The structure was solved by direct methods
and expanded by full-matrix least-squares, where the final R and Rw
values were 0.057 and 0.069, respectively, for 2499 reflections.
indicated that the dimerization proceeds via the singlet
excited state by direct irradiation.

2
-Alkoxynicotinates to Cage-Type Photodimers
J . Org. Chem., Vol. 67, No. 6, 2002 1845
F igu r e 3. Orbital surface diagram of methyl 2-methoxy-
nicotinate 1a obtained from the PM3 Hamiltonian contained
within MacSpartan.
Sch em e 1
F igu r e 2. (a) Fluorescence spectrum of 1f at the concentration
-
3
of 1.0 × 10 in EPA at room temperature, excitation at 290
nm, band-pass 3 nm. (b) Fluorescence spectrum of 1f at the
-
3
concentration of 1.0 × 10 in EPA at 77nK, excitation at 290
nm, band-pass 1.5 nm.
Contrary to the above, phenyl ester 1f did not exhibit
any emission at room temperature (Figure 2(a)); however,
emissive excimer was observed at 77 K (Figure 2(b)).
Photo-Fries rearrangement of 1f proceeded from its
singlet excited state, which was also determined by
sensitization and quenching experiments. These results
indicate that photo-Fries rearrangement initiated by
homolytic cleavage of the bond between carbonyl and
oxygen from the singlet excited state could be faster than
dimerization or fluorescence emission at room tempera-
ture. The difference in the reaction course was clearly
due to the stability of the radical pair intermediate
making the C(dO)-O bond cleavage process a more facile
process.
Pac et al. and Noh et al. individually investigated the
cycloaddition of 1-cyanonaphthalene to furan and de-
tected two diastereomeric 4π + 4π adducts by NMR
21-23
spectroscopy.
Furthermore, recently we reported the
24
photochemical addition of cyanopyridine with furan,
where the 4π + 4π photocycloadducts are also directly
detected by NMR spectra. A deuterated benzene solution
of 1a was irradiated with and without 2,5-dimethylhexa-
The regioselectivity and stereoselectivity in many
singlet photoadditions can be explained by orbital inter-
actions.2 Frontier-MO calculations by the PM3 method
2
,4-diene as a triplet quencher, because in the case of
the cyanopyridine-furan system, a 4π + 4π photocyclo-
5,26
adduct was detected only in the presence of a triplet
2
7
help to explain the photocycloaddition. The orbital
surfaces of the HOMO and LUMO of 1a were obtained
from the PM3 Hamiltonian contained within MacSpartan
as shown in Figure 3. The orbital interaction between
each LUMO supports the photocycloaddition leading to
isolable dimer 2a . The coefficient values of C3 and C6
positions of LUMO are bigger than the other positions,
and the interaction of these positions are suggested;
however, both the 4π + 4π addition between C3-C6′ and
the C6-C3′ (path A mechanism) and 2π + 2π cyclo-
addition between C3-C4 and C6′-C5′ (path B mecha-
nism) are supported as shown in Scheme 1.
24
quencher. Actually, irrespective of the presence of a
triplet quencher, only the peaks derived from the dimer
2
a were observed even if the reaction was checked in an
early step of the reaction. Under these conditions, it
seems that the absorbance of nonconjugated intermediate
4
is small and most of the light is absorbed by the starting
nicotinate 1; these facts indicate that an effective cy-
clization to dimer 2 involves two consecutive 2π + 2π
photocycloadditions via path B mechanism. In this case,
conjugated ester function and the diene chromophore of
intermediated 5 can react subsequent 2π + 2π photo-
cycloaddition effectively.
Furthermore, to look into the formation of a diastereo-
meric dimer, low-temperature photolysis was tried. When
a deuterated toluene solution of 1a was irradiated in the
NMR tube at -60 °C, the dimerization proceeded quite
slowly and formed only 2a , and no other products such
as a diastereomer could be detected. In this photodimer-
ization, the dipole-dipole interaction, the steric repulsion
between two ester groups and the secondary photochemi-
(
20) Murov, S. L. Handbook of Photochemistry; Marcel Dekker: New
York, 1973.
(
(
21) Pac, C.; Sugioka, T.; Sakurai, H. Chem. Lett. 1972, 39.
22) Mizuno, K.; Pac, C.; Sakurai, H. J . Chem. Soc., Perkin Trans.
1
1974, 2360.
(
23) Noh, T.; Kim, D. Tetrahedron Lett. 1996, 52, 9329.
(24) Sakamoto, M.; Kinbara, A.; Yagi, T.; Takahashi, M.; Yamaguchi
K.; Mino, T.; Watanabe, S.; Fujita, T. J . Chem. Soc., Perkin Trans. 1
999, 171.
25) Yang, N. C.; Gan, H.; Kim. S. S.; Masnovi, J . M. Tetrahedron
Lett. 1990, 31, 3825.
26) Somekawa, K.; Okuhira, H.; Sendayama, M.; Suishu, T.; Shimo,
T. J . Org. Chem. 1992, 57, 5708.
1
(
(
(27) Stewart, J . J . P. J . Comput. Chem. 1989, 10, 221.

1
846 J . Org. Chem., Vol. 67, No. 6, 2002
Sakamoto et al.
+
cal reaction may be important factors responsible for the
diastereoselective formation of 2.28
19 2 6
2a . HRMS (FAB) calcd for C16H N O (MH ) 335.1243, found
335.1211. Mp 156-157 °C. IR (CHCl ): 1652, 1743, 2956, 2996.
3
1
H NMR: 2.89 (dt, J ) 7.8 and 7.1 Hz, 2H, 2- and 8-H), 3.29
In conclusion, we have provided the first example of
the photochemical dimerization of 2-alkoxynicotinates
leading to C2-symmetrical cage-type photodimers. The
substituents on the pyridine ring exert considerable
influence on the photodimerization, and an additional
methyl group at the 6-position or an exchange to a phenyl
ester prevents the dimerization. Furthermore, we also
examined the photochemical reaction of 2-methoxy-4-
pyridinecarboxylic acid methyl ester, methyl nicotinate,
(
(
t, J ) 7.1 Hz, 2H, 1- and 7-H), 3.68 (s, 6H, C(dN)OMe), 3.80
13
s, 6H, COOMe) and 5.23 (d, J ) 7.8 Hz, 2H, 3- and 9-H).
C
NMR: 27.1, 35.1, 52.7, 53.3, 55.6, 57.7, 164.2, 172.3.
,11-Dim eth oxy-4,10-d ia za p en ta cyclo[6.4.0.0 .03,12.06,9]-
2,7
5
d od eca -4,10-d ien e-6,12-d ica r boxylic Acid Dieth yl Ester
+
2b. HRMS (FAB) calcd for C18
H
23
N
2
O
6
363.1556 (MH ), found
): 1657, 1736, 2943, 2989.
H NMR: 1.28 (t, J ) 7.1 Hz, 6H, CH CH ), 2.89 (dt, J ) 7.8
and 7.0 Hz, 2H, 2- and 8-H), 3.27 (t, J ) 7.0 Hz, 2H, 1- and
-H), 3.68 (s, 6H, C(dN)OMe), 4.24 (m, 4H, CH CH ) and 5.24
3
63.1550. Mp 113-115 °C. IR (CHCl
3
1
2
3
7
(
2
3
2
-methoxynicotinic acid; however, they are inert toward
13
d, J ) 7.8 Hz, 2H, 3- and 9-H); C NMR: 12.9, 26.0, 34.0,
2
9,30
photolysis under the same conditions.
We were now
5
2.0, 54.5, 56.3, 60.4, 163.2, 170.7.
5,11-Dieth oxy-4,10-d ia za p en ta cyclo[6.4.0.02,7.03,12.06,9]-
continuing investigations to explore this unique photo-
dimerization.
d od eca -4,10-d ien e-6,12-d ica r boxylic Acid Dim eth yl Ester
+
2
3
c. HRMS (FAB) calcd for C18
63.1565. Mp 113-115 °C. IR (CHCl
H
23
N
2
O
6
(MH ) 363.1556, found
1
3
): 1651, 1739, 2978. H
Exp er im en ta l Section
2 3
NMR: 1.21 (t, J ) 7.1 Hz, 6H, CH CH ), 2.87 (dt, J ) 7.8 and
7
.0 Hz, 2H, 2- and 8-H), 3.28 (t, J ) 7.0 Hz, 2H, 1- and 7-H),
Melting points are uncorrected. FT-IR spectra are reported
-
1
1
13
3.78 (s, 6H, OMe), 4.11 (m, 4H) and 5.21 (d, J ) 7.8 Hz, 2H, 3-
in cm
. H and C NMR spectra were obtained in CDCl
3
and 9-H). 13C NMR: 14.0, 27.1, 35.1, 52.6, 55.7, 57.6, 61.5,
solutions at 300 MHz. Chemical shifts are reported in δ units,
parts per million (ppm) relative to the TMS as internal
standard. An Eikohsya 500-W, 1000-W high-pressure and a
1
63.6, 172.5.
,11-Dim eth oxy-4,10-d ia za p en ta cyclo[6.4.0.02,7.03,12.06,9]-
d od eca -4,10-d ien e-6,12-d ica r boxylic Acid Diisop r op yl
5
1
00-W low-pressure mercury lamps were used as irradiation
+
Ester 2d . HRMS (FAB) calcd for C20
H
27
N
2
O
6
(MH ) 391.1869,
): 1660, 1734,
987. H NMR: 1.24 (d, J ) 6.3 Hz, 6H, CH(CH ), 1.25 (d, J
6.3 Hz, 6H, CH(CH ), 2.90 (dt, J ) 8.0 and 7.1 Hz, 2H, 2-
and 8-H), 3.23 (t, J ) 7.1 Hz, 2H, 1- and 7-H), 3.67 (s, 6H,
OMe), 5.13 (sep, J ) 6.3 Hz, 2H, CH(CH ), 5.23 (d, J ) 8.0
Hz, 2H, 3- and 9-H). 13C NMR: 21.7, 22.0, 27.5, 35.5, 53.3, 56.0,
7.7, 69.3, 164.8, 171.7.
-(2-H yd r oxyb en zoyl)-2-m et h oxyp yr id in e 3f. HRMS
source.
found 391.1856. Mp 114-115 °C. IR (CHCl
3
P r ep a r a tion of 2-Alk oxy Nicotin ic Acid Ester s 1a -f.
1
2
3 2
)
Nicotinates 1a -f were obtained by substitution of 2-chloro-
)
3 2
)
nicotinic acid with sodium alkoxide, followed by esterification
with sulfuric acid in the corresponding alcohol. Nicotinates
a -c were identified by the accordance of its spectral data.1
5,16
3 2
)
1
Isop r op yl 2-Meth oxyn icotin a te 1d . HRMS (FAB) calcd
5
+
for C
9
H
12NO
3
(MH ) 182.0817, found 182.0811. (Colorless oil)
3
bp 40-45 °C/4 mmHg. IR (CHCl
3
): 1583, 1729. 1H NMR
): 1.36 (d, J ) 6.2 Hz, 6H, CH(CH ), 4.04 (s, 3H, OMe),
.25 (sep, J ) 6.2 Hz, 1H, CH(CH ), 6.94 (dd, J ) 4.9 and
.5 Hz, 1H, 5-H), 8.12 (dd, J ) 2.0 and 7.5 Hz, 1H, 4-H), 8.29
+
(
FAB) calcd for C13
H
12NO
3
(MH ) 230.0817, found 230.0822.
): 1581, 1625, 3100 (br). H NMR:
.93 (s, 3H, OMe), 6.8-6.85 (m, 1H), 7.01-7.07 (m, 2H), 7.45-
.50 (m, 1H), 7.63-7.66 (m, 1H), 8.33-8.35 (m, 1H), 12.01 (s,
H, OH). 13C NMR: 54.2, 116.8, 118.7, 119.3, 120.1, 122.1,
33.7, 137.3, 138.5, 149.7, 160.8, 163.4, 200.5.
(CDCl
3
3 2
)
1
Mp 103-105 °C. IR (CHCl
3
5
7
(
3 2
)
3
7
1
1
dd, J ) 2.0 and 4.9 Hz, 1H, 6-H). 13C NMR: 22.3, 54.4, 69.0,
1
15.1, 116.6, 141.2, 150.8 162.9, 164.8.
Meth yl 2-Meth oxy-6-m eth yln icotin a te 1e. MS (FAB)
3
-(4-Hyd r oxyben zoyl)-2-m eth oxyp yr id in e 3′f. HRMS
+
calcd for C10
3
(
7
5
H
14NO
3
(MH ) 196, found 196. (Colorless oil) bp
+
(
FAB) calcd for C13
H
12NO
3
(MH ) 230.0817, found 230.0812.
): 1576, 1643, 3363. H NMR: 3.90
1
5-40 °C/6 mmHg. IR (CHCl
3
): 1594, 1733. H NMR: 2.48
1
Mp 164-165 °C. IR (CHCl
(
3
s, 3H, 6-Me), 3.88 (s, 3H, COOMe), 4.03 (2-OMe), 6.78 (d, J )
s, 3H, OMe), 6.76 (brs, 1H, OH), 6.87 (d, J ) 10.8 Hz, 2H,
1
3
.7 Hz, 1H, 5-H), 8.08 (d, J ) 7.7 Hz, 1H, 4-H). C NMR: 24.8,
Ph), 7.00 (dd, J ) 5.1 and 7.2 Hz, 1H, 5-H), 7.68 (dd, J ) 1.9
and 7.2 Hz, 1H, 4-H), 7.76 (d, J ) 10.8 Hz, 2H, Ph), 8.31 (dd,
2.4, 54.3, 110.8, 115.9, 141.9, 161.6, 162.3, 166.0.
P h en yl 2-Meth oxyn icotin a te 1f. HRMS (FAB) calcd for
13
J ) 1.9 and 5.1 Hz, 1H, 6-H). C NMR: 53.7, 115.4, 116.5,
+
C
13
H
12NO
3
(MH ) 230.0817, found 230.0813. Mp 120-125 °C.
1
23.0, 129.9, 132.7, 138.6, 148.8, 160.9, 161.0, 193.6.
1
IR (CHCl ): 1583, 1739. H NMR: 4.08 (s, 3H, OMe), 7.00-
3
X-r a y Cr yst a llogr a p h ic An a lysis of 2a . The dimer 2a
gave prismatic crystals of monoclinic space group P2 /c (No.
1
7
8
1
.03 (m, 1H), 7.20-7.27 (m, 3H), 7.40-7.43 (m, 2H), 8.36-
13
.40 (m, 2H). C NMR: 54.6, 116.8, 122.1, 126.3, 129.8, 142.1,
51.2, 151.9, 163.3, 163.7, 182.8.
1
9
1
4), a ) 12.661(4) Å, b ) 7.399(1) Å, c ) 16.810(10) Å, â )
3
-3
2.08(3)°, V ) 1573(1) Å , Z ) 4, F ) 1.411 gcm , µ(Cu KR) )
Gen er a l P r oced u r e for th e P h otoch em ica l Rea ction
-1
.09 cm , F(000) ) 704.00. The structure was solved by direct
of 2-Alk oxyn icotin a tes 1a -f. A benzene solution containing
methods and expanded by full-matrix least-squares, where the
2
-alkoxynicotinate 1 was deaerated by bubbling argon for 15
final R and Rw values were 0.057 and 0.069, respectively, for
min and was irradiated by Pyrex filtered light with a 1000-W
high-pressure mercury lamp at 15-20 °C. After irradiation,
the solvent was removed in vacuo, and the residual mixture
was subjected to chromatography on silica gel (eluant, n-
hexane/ethyl acetate). The crystalline photoproducts were
recrystallized from a mixture of chloroform and hexane. The
structure of photoproducts was determined on the basis of the
spectral data. Furthermore, the structure of 2a was estab-
lished by X-ray crystallographic analysis.
2
499 reflections.
Qu a n tu m Yield Mea su r em en t of 1a . All quantum yields
were determined at <20% conversion of the nicotinate using
light filtered through a K CrO /Na CO solution with a 500-W
2
4
2
3
high-pressure mercury lamp. The light flux was calibrated
using a valerophenone actinometer. The amount of products
formed in each irradiation was determined by NMR spectros-
copy.
Sen sitiza tion Exp er im en ts of Nicotin a tes 1f. Sensitiza-
tion was carried out by irradiating a benzene solution of
5
,11-Dim eth oxy-4,10-d ia za p en ta cyclo[6.4.0.02,7.03,12.06,9]-
d od eca -4,10-d ien e-6,12-d ica r boxylic Acid Dim eth yl Ester
2 4 2 3
nicotinates with light at 313 nm using a K CrO /Na CO
solution filter. A benzene solution of 1f (0.02 M) and triplet
sensitizers (3-methoxyacetophenone) was irradiated under
conditions where the sensitizers should absorb >95% of the
incident light. After the solvent was removed in vacuo, the
crude reaction mixture was analyzed by H NMR spectroscopy,
with response for product distribution.
(
28) Gercia H.; Gilbert A.; Griffiths, O. J . Chem. Soc., Perkin Trans.
1994, 247.
29) Irradiation of an alcoholic solution of nicotinate in the presence
2
(
of sulfuric acid resulted in alkylation and alkokylation. Sugimori, A.;
Tobita, E.; Kumagai, Y.; Sato, G. P. Bull. Chem. Soc. J pn. 1981, 54,
1
1
761.
30) Sugiyama, T.; Furihata, T.; Takagi, K.; Sata. M.; Akiyama, S.;
Sato, G. P.; Sugimori, A. Bull. Chem. Soc. J pn. 1981, 54, 3785.
(
Qu en ch in g Exp er im en ts of Nicotin a tes 1a a n d 1f. The
irradiation was performed at 313 nm using a K CrO /Na CO
2 4 2 3

2
-Alkoxynicotinates to Cage-Type Photodimers
J . Org. Chem., Vol. 67, No. 6, 2002 1847
solution filter. A benzene solution of 1a (0.05 M) or 1f (0.02
M) containing triplet quenchers (0.02 M) was irradiated. The
quenchers do not absorb light in the excitation region of
Su p p or tin g In for m a tion Ava ila ble: Crystal structure
data for 2a . This material is available free of charge via the
Internet at http://pubs.acs.org.
1
nicotinates. The reactions were monitored by H NMR spec-
troscopy.
J O016315U