Photochemical preparation of pyrimidin-2(1 H)-ones by rhenium(I) complexes with visible light

Article abstract of DOI:10.1021/jo102062u

With visible light irradiation (λ > 400 nm) of rhenium(I) complexes (P1-P4), a photochemical conversion from 3,4-dihydropyrimidin-2(1H)- ones to pyrimidin-2(1H)-ones at room temperature has been achieved with good to excellent yields in CH₃CN-H

Full text of DOI:10.1021/jo102062u

pubs.acs.org/joc
oxidation potential compared with that of dihydropyri-
4
dines. In general, excess corrosive and strong oxidants, such
Photochemical Preparation of Pyrimidin-2(1H)-ones
by Rhenium(I) Complexes with Visible Light
5
as DDQ, HNO , TBHP/CuCl , CAN/NaHCO , Co(NO ) /
6
7
8
3
2
10
3
3 2
12
9
11
K S O , K S O /ultrasound, TBHP/PhI(OAc)2, PCC,
2
2
8
2 2 8
Qiang Liu, Ya-Nan Li, Hui-Hui Zhang, Bin Chen,
Chen-Ho Tung, and Li-Zhu Wu*
þ 13
and NO , are required. These methods suffer from the use
of toxic reagents and the safety profile, low yield of the
products, and difficulty in product isolation. Developing
a method that can be applied in a wide range of DHPMs
with high yields under mild conditions is highly desirable. In
this regard, a photochemical process holds special promise.
Key Laboratory of Photochemical Conversion and
Optoelectronic Materials, Technical Institute of Physics and
Chemistry, Chinese Academy of Sciences,
Beijing 100190, P. R. China
1
4
Memarian and co-workers recently found that direct irra-
diation of DHPMs with UV light in a CHCl solution
lzwu@mail.ipc.ac.cn
3
resulted in the formation of pyrimidin-2(1H)-ones with
excellent yields. This is the first photochemical example for
dehydrogenation of DHPMs. In this reaction, UV light was
used to directly excite DHPMs, and the resultant pyrimidin-
Received October 18, 2010
2(1H)-ones also display absorption in this region that may
cause secondary photochemical reactions.
In the present work, we report a photochemical protocol
for facile preparation of pyrimidin-2(1H)-ones with visible
light. Herein, rhenium(I) complex was selected as a photo-
sensitizer in view of its visible light absorption, long excited-
state lifetime, strong excited-state redox potential, and ther-
1
5,16
mal and photochemical stability.
complex has been exploited for CO reduction, there are
Although this kind of
1
6
2
With visible light irradiation (λ > 400 nm) of rhenium(I)
complexes (P1-P4), a photochemical conversion from
3
ones at room temperature has been achieved with good
few reports on the use of rhenium(I) tricarbonyl diimine
complexes in organic synthesis. As compared with well
1
developed ruthenium(II) or platinum(II)
7
3d,18,19
,4-dihydropyrimidin-2(1H)-ones to pyrimidin-2(1H)-
complexes,
the excited rhenium(I) complexes possess more powerful
redox potential. This unique feature prompted us to initiate
a study on the dehydrogenation of DHPMs by rhenium(I)
complexes under visible light irradiation, where DHPMs and
pyrimidin-2(1H)-ones do not absorb, thereby avoiding pro-
duction of undesired products. As will be discussed later,
upon irradiation with visible light (λ > 400 nm), a catalytic
to excellent yields in CH CN-H O solution containing
3
2
CCl and K CO . Luminescence quenching study and
4
2
3
product analysis reveal that photoinduced electron trans-
fer between rhenium(I) complex P and 3,4-dihydropyrimi-
din-2(1H)-ones plays an important role in the initial event.
(
4) (a) Atwal, K. S.; Rovnyak, G. C.; Kimball, S. D.; Floyd, D. M.;
The construction of the functionalized pyrimidin-2(1H)-
one moiety is of significance due to its occurrence in many
biologically active and medicinally significant structures.
Moreland, S.; Swanson, B. N.; Gougoutas, J. Z.; Schwartz, J.; Smillie, K. M.;
Malley, M. F. J. Med. Chem. 1990, 33, 2629. (b) Vanden Eynde, J. J.;
Audiart, N.; Canonne, V.; Michel, S.; Van Haverbeke, Y.; Kappe, C. O.
Heterocycles 1997, 45, 1967.
1
From a synthetic point of view, dehydrogenation of 3,4-
dihydropyrimidin-2(1H)-ones (DHPMs) offers an attractive
method for making pyrimidin-2(1H)-ones because DHPMs
are easily prepared by Biginelli three-component coupling
(5) Watanabe, M.; Koike, H.; Ishiba, T.; Okada, T.; Seo, S.; Hirai, K.
Bioorg. Med. Chem. 1997, 5, 437.
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2
001, 38, 1345.
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2
reaction. However, unlike a large number of protocols
available for achieving nearly quantitative transformation
(
(
9) Shanmugam, P.; Perumal, P. T. Tetrahedron 2007, 63, 666.
10) Memarian, H. R.; Farhadi, A. Ultrason. Sonochem. 2008, 15, 1015.
3
of Hantzsch dihydropyridine to pyridine, the dehydrogena-
tion of DHPMs is extremely difficult owing to its higher
(11) Karade, N. N.; Gampawar, S. V.; Kondre, J. M.; Tiwari, G. B.
Tetrahedron Lett. 2008, 49, 6698.
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(
1) (a) Rizzo, R. C.; Tirado-Rives, J.; Jorgensen, W. L. J. Med. Chem.
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8, 1.
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Commun. 1998, 2451. (b) Zhu, X.-Q.; Zhao, B.-J.; Cheng, J.-P. J. Org. Chem.
2009, 20, 1183.
2
(14) (a) Memarian, H. R.; Farhadi, A. Monatsh. Chem. 2009, 140, 1217.
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(
6
(
2
2
000, 65, 8158. (c) Nakamichi, N.; Kawashita, Y.; Hayash, M. Org. Lett.
002, 4, 3955. (d) Zhang, D.; Wu, L.-Z.; Zhou, L.; Han, X.; Yang, Q. Z.;
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1
444 J. Org. Chem. 2011, 76, 1444–1447
Published on Web 02/01/2011
DOI: 10.1021/jo102062u
r 2011 American Chemical Society

Liu et al.
JOCNote
TABLE 1. Optimization of Photochemical Dehydrogenation Conditions
(Table 1, entry 2). Moreover, no conversion could be ob-
served when the reaction was carried out in the dark (Table 1,
entry 3). The results suggest that both light and rhenium(I)
complex are essential for the dehydrogenation and that
rhenium(I) complex remarkably accelerates the photochem-
ical transformation.
With the initial success, several rhenium(I) tricarbonyl
diimine complexes (P1-P4) were screened, and rhenium(I)
complex P2 was found to be the most efficient for the reac-
tion (Table 1, entries 4-6). As tabulated in Table 1, irradiat-
ing a solution of CH CN and CCl containing 1a and P2 for
3
4
1
However, no reaction took place at all when CHCl was used
2 h resulted in the formation of 2a in a yield of 61%.
3
a
b
to replace CCl (Table 1, entry 7), and the use of CH NO as
3
4
2
entry
conditions
yield (%)
oxidant only afforded 2a in 15% yield (Table 1, entry 8).
Evidently, CCl is a crucial terminal oxidant in the reaction.
1
2
3
4
5
6
7
8
9
P1 (15 mol %), CCl
4
5 mL
33
0
0
61
23
37
0
15
82
4
no catalyst, CCl
no light, P1 (15 mol %), CCl
4
5 mL
c
It was worth noting that after irradiation the solution
became acidic and chloroform was detected by GC in addi-
tion to 2a. Considering that acidic hydrogen chloride may
inhibit the production of pyrimidin-2(1H)-one 2a, aqueous
solution of K CO was added to consume the acid generated
4
5 mL
P2 (15 mol %), CCl
P3 (15 mol %), CCl
P4 (15 mol %), CCl
4
4
4
5 mL
5 mL
5 mL
P2 (15 mol %), CHCl
P2 (15 mol %), CH NO
P2 (15 mol %), CCl 5 mL,
CO (9 equiv), H
3
5 mL
2
3
3
2
5 mL
during the reaction. As expected, the isolated yield of 2a was
improved from 61% to 82% with the addition of aqueous
K CO (9 equiv) to the dehydrogenation system (Table 1,
4
K
2
3
2
O, 5 mL
a
-3
b
M. Isolated yield after
The concentration of 1a is 2 ꢀ 10
2
3
c
. Stirred at room temperature
purification by chromatography on SiO
for 12 h.
2
entry 9).
A survey of a series of substituted DHPMs demonstrated
that the DHPMs bearing alkyl and aryl substituents could be
successfully transformed to their corresponding pyrimidin-
2(1H)-ones in good to excellent yields under the optimized
conditions, i.e., 1.0 mmol of DHPM substrate, 0.15 mmol of
amount of rhenium(I) complex P1-P4 is capable of produc-
ing pyrimidin-2(1H)-ones with good to excellent yields.
The photochemical reaction was carried out in degassed
solution at room temperature. Typically, 50 mL of a satu-
Re(I)(Phen)(CO)
solution of CH
Br (P2), and 9.0 mmol of K
CO in a
2 3
3
rated CH CN solution of DHPM substrate and rhenium(I)
3
3
CN, CCl and H O (V/V: 10:1:1) under
4
2
complex P in a Pyrex reactor was irradiated by a 500-W high-
pressure Hanovia mercury lamp. A glass filter was used to
cut off light below 400 nm, thereby guaranteeing that only
rhenium(I) complex P was irradiated, while DHPMs and
pyrimidin-2(1H)-ones are transparent (Figure S1 in Sup-
porting Information). To our delight, pyrimidin-2(1H)-one
visible light irradiation (λ > 400 nm). It was reported that
a methyl group located at C-6 of DHPMs is sensitive to harsh
9
dehydrogenation conditions. Undesired byproduct such
as nitrolic acids, dealkylated pyrimidin-2(1H)-ones, and
6
pyrimidin-2,4(1H,3H)-diones were often obtained when HNO ,
3
8
9
CAN, or Co(NO ) /K S O were used as strong oxidants.
3 2 2 2 8
2
(
a was produced in a yield of 33% by 15 mol % Re(I)(bipy)-
CO) Br P1 when CCl4 was present (Table 1, entry 1),
In our case, however, no any dealkylation product could be
detected under the reaction conditions (Table 2, entries 1-5).
Substrates with a phenyl group at the C-6 position afforded
the desired dehydrogenated products in much higher yields
3
whereas irradiation of 1a in the absence of Re(I) complex
with visible light at λ > 400 nm led to no product formation
(Table 2, entries 6-8). Furthermore, with the visible light
irradiation the S-alkylated DHPMs 3 could be successfully
converted to their corresponding 2-methylthio-pyrimidines 4
in excellent yields (Scheme 1).
(
17) (a) Nicewicz, D. A.; MacMillan, D. W. C. Science 2008, 322, 77.
b) Ischay, M. A.; Anzovino, M. E.; Du, J.; Yoon, T. P. J. Am. Chem. Soc.
008, 130, 12886. (c) Koike, T.; Akita, M. Chem. Lett. 2009, 38, 166.
d) Borak, J. B.; Falvey, D. E. J. Org. Chem. 2009, 74, 3894. (e) Du, J.; Yoon,
(
2
(
Since the solution became acidic, with accompanying for-
mation of chloroform upon irradiation, we tentatively pro-
posed an electron transfer mechanism for the photocatalytic
dehydrogenation reaction shown in Scheme 2. When irra-
T. P. J. Am. Chem. Soc. 2009, 131, 14604. (f) Nagib, D. A.; Scott, M. E.;
MacMillan, D. W. C. J. Am. Chem. Soc. 2009, 131, 10875. (g) Narayanam,
J. M. R.; Tucker, J. W.; Stephenson, C. R. J. J. Am. Chem. Soc. 2009, 131, 8756.
(
h) Tucker, J. W.; Narayanam, J. M. R.; Krabbe, S. W.; Stephenson, C. R. J.
Org. Lett. 2010, 12, 368. (i) Condie, A. G.; Gonzalez-Gomez, J. C.; Stephenson,
C. R. J. J. Am. Chem. Soc. 2010, 132, 1464. (j) Ischay, M. A.; Lu, Z.; Yoon, T. P.
J. Am. Chem. Soc. 2010, 132, 8572. (k) Furst, L.; Matsuura, B. S.; Narayanam,
J. M. R.; Tucker, J. W.; Stephenson, C. R. J. Org. Lett. 2010, 12, 3104.
(18) (a) Roundhill, D. M.; Gray, H. B.; Che, C. M. Acc. Chem. Res. 1989,
2, 55. (b) Du, P.; Schneider, J.; Jarosz, P.; Eisenberg, R. J. Am. Chem. Soc.
006, 128, 7726. (c) Du, P.; Schneider, J.; Li, F.; Zhao, W.; Patel, U.;
3
diated with visible light, the MLCT excited state of rhe-
nium(I) complex P is reductively quenched by DHPMs 1 to
- •
give reduced rhenium(I) complex P and the radical cation
þ •
2
2
of DHPMs 1 , which was well evidenced by the luminescence
quenching experiment (Supporting Information). Rhenium(I)
Castellano, F. N.; Eisenberg, R. J. Am. Chem. Soc. 2008, 130, 5056.
19) (a) Li, X. H.; Wu, L.-Z.; Zhang, L. P.; Tung, C. H.; Che, C. M. Chem.
complex P exhibits broad absorption bands between
3
(
3
-1
-1
Commun. 2001, 2280. (b) Zhang, D.; Wu, L.-Z.; Yang, Q. Z.; Li, X. H.;
Zhang, L. P.; Tung, C. H. Org. Lett. 2003, 5, 3221. (c) Yang, Y.; Zhang, D.;
Wu, L.-Z.; Chen, B.; Zhang, L. P.; Tung, C. H. J. Org. Chem. 2004, 69, 4788.
250 and 450 nm with ε on the order of 10 dm mol cm
Figure S1 in Supporting Information). With reference to
(
15
(
d) Feng, K.; Zhang, R. Y.; Wu, L.-Z.; Tu, B.; Peng, M. L.; Zhang, L. P.;
previous spectroscopic work on rhenium(I) complexes, the
absorption bands at 380-450 nm are ascribed to the dπ(Re) f
π*(N-N) MLCT state. Excitation of the characteristic
absorption of rhenium(I) complex P at 400 nm resulted in
Zhao, D.; Tung, C. H. J. Am. Chem. Soc. 2006, 128, 14685. (e) Feng, K.; Wu,
L.-Z.; Zhang, L. P.; Tung, C. H. Tetrahedron 2007, 63, 4907. (f) Wang, D.-H.;
Peng, M.-L.; Han, Y.; Chen, B.; Tung, C. H.; Wu, L.-Z. Inorg. Chem. 2009,
4
8, 9995.
J. Org. Chem. Vol. 76, No. 5, 2011 1445

Liu et al.
SCHEME 2. Plausible Mechanism for the Dehydrogenation
JOCNote
a
TABLE 2. Photochemical Preparation of Pyrimidin-2(1H)-ones
1
R
2
R
b
entry
substrate
product
yield (%
1
2
3
4
5
6
7
8
a
Me
Me
Me
Me
Me
Ph
H
1a
1b
1c
1d
1e
1f
2a
2b
2c
2d
2e
2f
82
88
91
86
84
84
91
90
Me
OMe
Cl
Br
H
of rhenium(I) complexes (P1-P4), 3,4-dihydropyrimidin-
(1H)-ones DHPMs can be successfully converted to pyr-
2
Ph
Ph
Me
Cl
1g
1h
2g
2h
imidin-2(1H)-ones with good to excellent yields in CH CN-
3
H O solution at room temperature, in which CCl4 and
K CO are important for improving the reaction efficiency.
2
Reactions conducted using substrate (1.0 mmol), Re(I)(Phen)(CO)
Br (0.15 mmol), K CO (9.0 mmol), H O (5 mL), and CCl (5 mL) in
degassed CH CN (50 mL) under irradiation by a 500-W high-pressure
mercury lamp. A glass filter was used to cut off light below 400 nm.
3
-
2
3
2
3
2
4
Luminescence quenching study and product analysis reveal
that photoinduced electron transfer between rhenium(I)
complex P and DHPMs plays an important role in this reac-
tion. Efforts toward further mechanistic understanding and
extension of the dehydrogenation are currently underway.
3
b
Isolated yield after purification by chromatography on SiO
2
SCHEME 1. Photochemical Dehydrogenation of 2-Methylthio
pyrimidines
Experimental Section
General Procedure for the Photochemical Preparation of Pyr-
imidin-2(1H)-ones. To a mixture of ethyl 1,2,3,4-tetrahydro-6-
methyl-2-oxo-4-phenylpyrimidine-5-carboxylate 1a (1.0 mmol),
Re(I)(Phen)(CO)
5
3
Br (0.15 mmol), and K
2
CO
3
(9.0 mmol in
(5 mL). The
2 3
mL H O) were added CH CN (50 mL) and CCl
4
solution was divided into two 50-mL Pyrex tubes and degassed
for 40 min by Argon. The resultant mixture was then irradiated
by a 500-W high-pressure mercury lamp at ambient tempera-
ture. A glass filter was employed to cut off light with wavelength
below 400 nm. The progress of the reaction was monitored by
thin-layer chromatography at regular intervals. Generally, after
a maximal luminescence at 600 nm (Figure S2 in Supporting
Information). Progressive addition of DHPMs 1 into the
solution of rhenium(I) complex P quenched the lumines-
cence, but in sharp contrast, the similar quenching behavior
was absent when CCl was introduced (Figure S3 in Sup-
4
porting Information). These results suggest no significant
electronic interaction between rhenium(I) complex P and
1
2 h of irradiation the conversion was close to 100%. Upon
removal of solvent in vacuo, the residue was diluted with 30 mL
of CH Cl and washed with saturated aqueous NH
Cl (3 ꢀ
10 mL). The residue was purified by column chromatography on
silica gel eluting with CH Cl /ethyl acetate = 4:1, and the
2
2
4
2
2
fraction with R = 0.15 was collected and concentrated to give
f
CCl in the excited state, but indeed between rhenium(I)
4
the target ethyl 1,2-dihydro-6-methyl-2-oxo-4-phenylpyrimi-
dine-5-carboxylate 2a as a pale yellow solid, which was identi-
complex P and DHPMs 1. The reductive quenching of rhe-
nium(I) complex P by DHPMs 1 was further strengthened by
the fact that after irradiation Re(I)(Phen)(CO) Br was partly
1 13
fied by H and C NMR spectroscopy and MS spectrometry.
Ethyl 1,2-Dihydro-6-methyl-2-oxo-4-phenylpyrimidine-5-
3
1
carboxylate (2a). H NMR (DMSO-d
6
, 400 MHz) δ 0.82 (t, 3H,
transformed to Re(I)(Phen)(CO) Cl, implying the genera-
3
J = 7.1 Hz), 2.40 (s, 3H), 3.94 (q, 2H, J = 7.2 Hz), 7.39-7.51 (m,
tion of one-electron-reduced species rhenium(I) complex
- •
13
5
H), 12.39 (s, 1H); C NMR (DMSO-d , 100 MHz) δ 13.2, 18.4,
-
• 16e
6
P
reacted with CCl to regenerate rhenium(I) complex P and
.
The reduced rhenium(I) complex P
is in turn
6
171.7; EI-MS m/z (%) 258 (M , 45), 229 (100), 213 (67), 185
0.8, 109.0, 127.5, 128.2, 128.7, 130.1, 138.2, 155.4, 160.8, 165.9,
þ
4
•
to produce CCl3 radical and chloride anion. Then the fast
þ•
(34), 104 (28), 77 (11).
Ethyl 1,2-Dihydro-6-methyl-2-oxo-4-p-tolylpyrimidine-5-
deprotonation of DHPMs 1 radical cation leads to the
•
1
formation of DHPMs 1 radical. Finally, the hydrogen
•
carboxylate (2b). H NMR (DMSO-d , 400 MHz) δ 0.88 (t, 3H,
6
abstraction by CCl3 radical completes the reaction giving
rise to chloroform and pyrimidin-2(1H)-ones 2. As suggested
J = 7.1 Hz), 2.356 (S, 3H), 2.372 (S, 3H), 3.98 (q, 2H, J =
1
3
7
1
6
.1 Hz), 7.26-7.36 (m, 4H), 12.37 (s, 1H). C NMR (DMSO-d ,
00 MHz) δ 13.4, 18.5, 20.9, 60.9, 109.1, 127.6, 128.8, 134.9,
140.2, 155.6, 161.1, 166.1, 171.6; EI-MS m/z (%) 272 (M , 32),
243 (100), 227 (27), 199 (9), 118 (7).
by one of the reviewers, it is also possible that chloroform is
•
þ
produced by reduction of CCl radical and subsequent
3
•
-
-
þ
protonation: CCl3 þ e f CCl ; CCl3 þ H f HCCl
3
3.
Ethyl 1,2-Dihydro-4-(4-methoxyphenyl)-6-methyl-2-oxopyri-
midine-5-carboxylate (2c). H NMR (DMSO-d , 400 MHz)
To summarize, we described a photochemical approach to
access pyrimidin-2(1H)-ones, important synthetic targets. The
dehydrogenation of DHPMs employs rhenium(I) complexes
as photosensitizers, and the whole process is environmen-
tally benign, i.e., with visible-light irradiation (λ > 400 nm)
1
6
δ 0.94 (t, 3H, J = 8.0 Hz), 2.36 (s, 3H), 3.81 (s, 3H), 4.03
(
q, 2H, J = 8.0 Hz), 7.02 (d, 2H, J = 8.0 Hz), 7.44 (d, 2H,
1
3
J = 8.0 Hz), 12.25 (s, 1H); C NMR (DMSO-d , 100 MHz) δ
6
13.5, 18.2, 55.4, 60.9, 108.9, 113.7, 129.5, 130.2, 155.5, 159.8,
1
446 J. Org. Chem. Vol. 76, No. 5, 2011

Liu et al.
61.2, 166.3, 171.1; EI-MS m/z (%) 288 (M , 86), 259 (100), 243
JOCNote
þ
1
(t, 3H, J = 8.0 Hz), 3.86 (q, 2H, J = 8.0 Hz), 7.49-7.60 (m, 9H),
12.65 (s, 1H); C NMR (DMSO-d , 100 MHz) δ 13.1, 61.2, 111.7,
6
127.9, 128.4, 128.5, 129.8, 130.5, 134.7 (br), 135.3, 157.5, 166.2; EI-
MS m/z (%) 356 (M , 4), 354 (22), 327 (13), 325 (100), 309 (21),
104 (6).
1
3
(
34), 219 (19), 134 (15), 69 (23).
Ethyl 4-(4-Chlorophenyl)-1,2-dihydro-6-methyl-2-oxopyrimi-
1
þ
dine-5-carboxylate (2d). H NMR (DMSO-d , 400 MHz) δ
6
0
7
.88 (t, 3H, J = 7.1 Hz), 2.41 (s, 3H), 3.98 (q, 2H, J = 7.1 Hz),
.45 (d, 2H, J = 8.4 Hz), 7.54 (d, 2H, J = 8,5 Hz), 10.74 (s, 1H).
Ethyl 4-Methyl-2-(methylthio)-6-phenylpyrimidine-5-carboxylate
1
3
1
(4a). H NMR (CDCl
2.57 (s, 3H), 2.62 (s, 3H), 4.15 (q, 2H, J = 8.0 Hz), 7.64 (d, 2H, J =
C NMR (DMSO-d
1
MS m/z (%) 294 (M , 10), 292 (43), 263 (100), 247 (52), 219 (15),
6
, 100 MHz) δ 13.3, 18.5, 60.9, 108.8, 128.0,
28.3, 129.4, 134.6, 135.0, 137.0, 155.3, 162.0, 165.6, 170.1; EI-
3
, 400 MHz) δ 1.04 (t, 3H, J = 8.0 Hz),
þ
13
3
8.0 Hz), 7.40-7.47 (m, 3H); C NMR (CDCl , 100 MHz) δ 13.7,
2
06 (13), 138 (18).
Ethyl 4-(4-Bromophenyl)-1,2-dihydro-6-methyl-2-oxopyrimi-
22.7, 29.8, 61.8, 121.1, 128.5, 128.6, 130.2, 137.9, 163.7, 165.6, 168.3,
172.6; EI-MS m/z (%) 288 (M , 100), 259 (13).
Ethyl 2-(Methylthio)-4,6-diphenylpyrimidine-5-carboxylate
þ
1
dine-5-carboxylate (2e). H NMR (DMSO-d , 400 MHz) δ 0.87
6
1
(4b). H NMR (CDCl
(
t, 3H, J = 7.1 Hz), 2.40 (s, 3H), 3.98 (q, 2H, J = 7.1 Hz), 7.38 (d,
3
, 400 MHz) δ 0.86 (t, 3H, J = 8.0 Hz),
13
13
2
1
1
H, J = 8.4 Hz), 7.68 (d, 2H, J = 8.4 Hz); C NMR (DMSO-d
6
,
2.62 (s, 3H), 4.01 (q, 2H, J = 8.0 Hz), 7.51-7.65 (m, 10H); C
00 MHz) δ13.3, 18.5, 60.9, 108.7, 123.6, 129.6, 131.3, 137.4, 155.4,
62.1, 165.6, 170.0; EI-MS m/z (%) 338 (M , 37), 336 (39), 308
NMR (CDCl , 100 MHz) δ 13.5, 29.7, 61.9, 120.9, 128.5, 130.2,
3
þ
þ
137.5, 164.4, 168.2, 172.8; EI-MS m/z (%) 350 (M , 100), 321
(91), 305 (56), 275 (45), 231 (65), 159 (32), 129 (84), 77 (54).
(
91), 306 (100), 293 (34), 291 (40), 184 (8), 182 (9).
Ethyl 1,2-Dihydro-2-oxo-4,6-diphenylpyrimidine-5-carboxy-
1
late (2f). H NMR (DMSO-d , 400 MHz) δ 0.74 (t, 3H, J =
6
Acknowledgment. Financial support from Solar Energy
Initiative of the Knowledge Innovation Program of the
Chinese Academy of Sciences (KGCXZ-YW-389), the Na-
tional Science Foundation of China (20732007, 21090343
and 50973125), the Ministry of Science and Technology of
China (G2007CB808004 and 2009CB220008), and the Bu-
reau for Basic Research of the Chinese Academy of Sciences
is gratefully acknowledged.
8
1
1
.0 Hz), 3.84 (q, 2H, J = 8.0 Hz), 7.48-7.57 (m, 10H), 12.59 (s,
13
6
H); C NMR (DMSO-d , 100 MHz) δ 13.1, 61.2, 111.7, 127.9,
28.5, 130.5, 135.2, 157.3, 165.3 (br), 166.4 ; EI-MS m/z (%) 320
þ
(
M , 18), 291 (100), 275 (15), 247 (72), 104 (12), 77 (5).
Ethyl 1,2-Dihydro-2-oxo-6-phenyl-4-p-tolylpyrimidine-5-
1
carboxylate (2g). H NMR (DMSO-d
6
, 400 MHz) δ 0.77 (t, 3H,
J = 8.0 Hz), 2.37 (s, 3H), 3.85 (q, 2H, J = 8.0 Hz), 7.31 (d, 2H,
J = 8.0 Hz), 7.44 (d, 2H, J = 8.0 Hz), 7.48-7.54 (m, 5H), 12.54
1
3
(
1
1
s, 1H); C NMR (DMSO-d
6
, 100 MHz) δ 13.1, 20.9, 61.1,
11.5, 127.8, 127.9, 128.4, 129.0, 130.4, 132.2, 135.4, 140.5,
Supporting Information Available: Experimental details,
UV-vis spectra of P2, 1a, 2a and CCl , luminescence quenching
experiments, H, C NMR spectra of dehydrogenation pro-
ducts and other data. This material is available free of charge via
the Internet at http://pubs.acs.org.
þ
þ
57.4, 166.5; EI-MS m/z (%) 334 (M , 63), 305 (M , 100), 289
4
1
13
(
54), 261 (18), 118 (13), 104 (12), 77 (4).
Ethyl 4-(4-Chlorophenyl)-1,2-dihydro-2-oxo-6-phenylpyrimi-
1
dine-5-carboxylate (2h). H NMR (DMSO-d
6
, 400 MHz) δ 0.76
J. Org. Chem. Vol. 76, No. 5, 2011 1447