Gallium(III) iodide-catalyzed Biginelli-type reaction under solvent-free conditions: Efficient synthesis of dihydropyrimidine-2(1H)-one derivatives

Article abstract of DOI:10.1002/cjoc.201090338

The Biginelli-type condensation of ethyl acetoacetate/cycloketone, aldehyde and urea/thiourea under solvent-free condition catalyzed by 10% gallium(III) iodide to form dihydropyrimidine-2(1H)-one derivatives was described. This process offered one way to

Full text of DOI:10.1002/cjoc.201090338

FULL PAPER
Gallium(III) Iodide-catalyzed Biginelli-type Reaction Under
Solvent-free Conditions: Efficient Synthesis of Dihydro-
pyrimidine-2(1H)-one Derivatives
Li, Dapenga(李大鹏)
Mao, Haifenga(茅海峰)
An, Litaob(安礼涛)
Huang, Zhihaoc(黄智豪)
Zou, Jianping*,a(邹建平)
a Key Laboratory of Organic Synthesis of Jiangsu Province, College of Chemistry and Chemical Engineering,
Suzhou University, 199 Renai Street, Suzhou, Jiangsu 215123, China
b Jiangsu Key Laboratory for Chemistry of Low-dimensional Materials, College of Chemistry and Chemical Engi-
neering, Huaiyin Normal University, Huai′an, Jiangsu 223300, China
c Department of Chemical Research, Suzhou Yaomigu Company, Suzhou, Jiangsu 215000, China
The Biginelli-type condensation of ethyl acetoacetate/cycloketone, aldehyde and urea/thiourea under sol-
vent-free condition catalyzed by 10% gallium(III) iodide to form dihydropyrimidine-2(1H)-one derivatives was de-
scribed. This process offered one way to constructing dihydropyrimidine-2(1H)-ones in good to excellent yields
with simple procedure and short reaction time.
Keywords Biginelli reaction, gallium(III) iodide, dihydropyrimidine-2(1H)-one, solvent-free, multicomponent
reaction, homogeneous catalysis
Introduction
aldehyde and urea in the presence of a catalytic amount
of HCl, however, the yields were low (20%—50%).5
Therefore, many chemists made many improvements in
the last decade, and developed some efficient Lewis
acid catalysts for Biginelli reaction, such as BF3•Et2O,
Yb(OTf)3, InX3, CeCl3.6-22 In course of our study on the
gallium salts, we found they were able to efficiently
catalyze the C—C and C—N bond formations.23 In this
paper, we wish to report the Biginelli-type reaction effi-
ciently catalyzed by gallium(III) iodide.
Organic reaction under solvent-free conditions has
gained in popularity in recent years.1 This is because
solvent free reaction has the advantages of short
reaction time, simple workup procedure, low cost and
environment friendly.
Dihydropyrimidinone is an important class of com-
pounds, which have interesting pharmacological proper-
ties used for calcium channel modulators, α -antago-
nists, anticancer drugs, Rho-kinase inhibitors, and
anti-HIV marine natural products.2-4 Therefore, de-
veloping efficient synthetic methods for such com-
pounds are much required.
The dihydropyrimidinone was first prepared by
Biginelli in 1893 from the reaction of ethyl acetoacetate,
1a
Experimental
1H and 13C NMR spectra were determined in CDCl3
on an Inova-400 MHz spectrometer and chemical
*
E-mail: jpzou@suda.edu.cn; Tel.: 0086-0512-65880336; Fax: 0086-0512-62521536
Received January 18, 2010; revised April 7, 2010; accepted May 7, 2010.
Project supported by the National Natural Science Foundation of China (No. 20772088).
Chin. J. Chem. 2010, 28, 2025— 2032
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Li et al.
FULL PAPER
shifts (δ) reported relative to internal TMS. Melting
points were determined on an XT-4 melting point appa-
ratus and uncorrected. High resolution mass spectra
were recorded on a Micromass OA-TOF (EI) mass
spectrometer. All of the reagents were used directly as
obtained commercially unless otherwise noted.
7.32 (d, J＝6.0 Hz, 1H, furan-H), 6.30—6.25 (m, 1H,
furan-H), 6.12 (d, J＝6.1 Hz, 1H, furan-H), 5.76 (s, 1H,
NH), 5.49 (s, 1H, CH), 4.15 (q, J＝7.2 Hz, 2H, CH2O),
2.36 (s, 3H, CH3), 1.22 (t, J＝7.2 Hz, 3H, CH3). HRMS
calcd for C12H14N2O4 (M＋) 250.0954, found 250.0945
(M＋, 54.48).
4f Yield 92%, m.p. 174—177 ℃ (Lit.9 175—177
1
General procedure for gallium(III) iodide-catalyzed
Biginelli-type reaction under solvent-free conditions
℃). H NMR (CDCl3, 400 MHz) δ: 8.15 (s, 1H, NH),
7.28—6.99 (m, 4H, ArH), 6.05 (s, 1H, NH), 5.39 (s, 1H,
CH), 4.09 (q, J＝7.2 Hz, 2H, CH2O), 2.33 (s, 3H, CH3),
1.17 (t, J ＝ 7.2 Hz, 3H, CH3). HRMS calcd for
C14H15N2O3F (M＋) 278.1067, found 278.1083 (M＋,
17.20).
Typical experimental procedure for preparation of 4a
—4k: GaI3 was prepared by stirring a mixture of Ga
metal (0.1 mmol) and I2 (0.15 mmol) in 2 mL CH2Cl2
(dried with P2O5) in flame-dried glassware. After
stirring the mixture of Ga and I2 for several hours, the
red color disappeared and the mixture became a trans-
parent liquid. To this solution aldehyde 1 (1 mmol),
ethyl acetoacetate 2 (or cycloketone 3) (1 mmol), and
urea (1.2 mmol) were added, the mixture was heated to
100 ℃ and stirred for 20 min. After the reaction was
completed (TLC analysis), the mixture was cooled to
room temperature, added with water, extracted with
ethyl acetate, and the organic layer was dried with an-
hydrous Na2SO4. The solvent was removed in reduced
pressure and the residue was recrystallized from metha-
nol or ethanol to afford the pure products 4 or 5 in good
to excellent yields.
4g Yield 79%, m.p. 215—216 ℃ (Lit.11d 216—217
1
℃). H NMR (CDCl3, 400 MHz) δ: 9.15 (s, 1H, CHO),
8.31 (s, 2H, ArH＋NH), 7.67 (s, 1H, ArH), 7.17 (s, 2H,
ArH), 5.13 (s, 1H, NH), 3.97 (q, J＝7.0 Hz, 2H, CH2O),
2.29 (s, J＝7.0 Hz, 3H, CH3), 1.09 (t, J＝7.2 Hz, 3H,
CH3).
4h Yield 84%, m.p. 194—195 ℃ (Lit.11b 194—195
1
℃). H NMR (CDCl3, 400 MHz) δ: 8.12 (s, 1H, NH),
5.71 (s, 1H, NH), 4.44—4.42 (m, 1H, CH), 4.19 (q, J＝
7.2 Hz, 2H, CH2O), 2.29 (s, 3H, CH3), 1.30—1.26 (m,
6H, 2 × CH3). HRMS calcd for C8H11N2O3 (M ＋ )
183.0743, found 183.0740 (M＋, 100.00).
4i Yield 82%, m.p. 205—206 ℃ (Lit.9 208—210
℃). 1H NMR (CDCl3, 400 MHz) δ: 8.12 (brs, 1H, NH),
5.85 (brs, 1H, NH), 4.34—4.28 (m, 1H, CH), 4.19 (q,
J＝7.1 Hz, 2H, CH2O), 2.29 (s, 3H, CH3), 1.56—1.52
(m, 2H, CH2), 1.35—1.15 (m, 4×CH2, 11H, CH3), 0.88
(t, J＝7.6 Hz, 3H, CH3).
Spectral data of 4a— 4k
4a Yield 95%, m.p. 202—203 ℃ (Lit.6 202—204
1
℃). H NMR (CDCl3, 400 MHz) δ: 8.04 (s, 1H, NH),
7.32—7.26 (m, 5H, ArH), 5.73 (s, 1H, NH), 5.04 (s, 1H,
CH), 4.07 (q, J＝7.2 Hz, 2H, CH2O), 2.35 (s, 3H, CH3),
1.17 (t, J ＝ 7.2 Hz, 3H, CH3). HRMS calcd for
C14H16N2O3 (M＋ ) 260.1161, found 260.1188 (M＋ ,
23.30).
4j Yield 87%, m.p. 225—227 ℃ (Lit.27 225 ℃).
1H NMR (CDCl3, 400 MHz) δ: 7.71 (s, 1H, NH), 7.24—
7.35 (m, 5H, ArH), 6.55—6.49 (m, 1H, CH), 6.24—
6.18 (m, 1H, CH), 5.58 (m, 1H, NH), 5.01—4.99 (m,
1H, CH), 4.19 (q, J＝7.1 Hz, 2H, CH2O), 2.32 (s, 3H,
CH3), 1.28 (t, J＝7.1 Hz, 3H, CH3). HRMS calcd for
C16H18N2O3 (M＋ ) 286.1317, found 286.1314 (M＋ ,
100.00).
4b Yield 90%, m.p. 211—212 ℃ (Lit.6 213—215
1
℃). H NMR (CDCl3, 400 MHz) δ: 7.40 (s, 1H, NH),
7.30—7.24 (m, 4H, ArH), 5.58 (s, 1H, NH), 5.38 (s, 1H,
CH), 4.09 (q, J＝7.1 Hz, 2H, CH2O), 2.34 (s, 3H, CH3),
1.17 (t, J ＝ 7.1 Hz, 3H, CH3). HRMS calcd for
C14H15N2O3Cl (M＋) 294.0771, found 294.0779 (M＋,
27.76).
4k Yield 90%, m.p. 232—234 ℃ (Lit.11b 232—234
1
℃). H NMR (CDCl3, 400 MHz) δ: 7.86 (s, 1H, NH),
7.27—7.25 (m, 5H, ArH), 5.37 (s, 1H, NH), 4.06 (q, J＝
7.2 Hz, 2H, CH2O), 2.34 (s, 3H, CH3), 1.14 (t, J＝7.2
Hz, 3H, CH3). HRMS calcd for C14H16N2O2S (M＋)
276.0932, found 276.0940 (M＋, 84.33).
4c Yield 91%, m.p. 219—220 ℃ (Lit.6 219—222
1
℃). H NMR (CDCl3, 400 MHz) δ: 8.07 (s, 1H, NH),
7.62—7.43 (m, 4H, ArH), 5.95 (s, 1H, NH), 5.46—5.45
(m, 1H, CH), 4.10 (q, J＝7.2 Hz, 2H, CH2O), 2.36 (s,
3H, CH3), 1.18 (t, J＝7.1 Hz, 3H, CH3). HRMS calcd
for C15H15N3O3 (M＋) 285.1131, found 285.1145 (M＋,
26.31).
Spectral data of 5a—5g
5a Yield 90%, m.p. 236—238 ℃ (Lit.22a 236—239
℃). 1H NMR (DMSO-d6, 400 MHz) δ: 8.77 (s, 1H, NH),
7.40—7.21 (m, 11H, ArH＋CH), 6.63 (s, 1H, NH), 5.15
(s, 1H, CH), 2.83—2.79 (m, 2H, CH2), 2.38—2.37 (m,
1H, CH), 2.03—1.97 (m, 1H, CH). HRMS calcd for
C20H18N2O (M＋) 302.1419, found 302.1418 (M＋, 100).
5b Yield 83%, m.p. 224—225 ℃ (Lit.22a 226—228
℃). 1H NMR (DMSO-d6, 400 MHz) δ: 8.83 (s, 1H, NH),
7.46—7.27 (m, 9H, ArH＋CH), 6.63 (s, 1H, NH), 5.19
(s, 1H, CH), 2.81—2.77 (m, 2H, CH2), 2.43—2.37 (m,
1H, CH), 2.02 — 1.96 (m, 1H, CH). 13C NMR
4d Yield 90%, m.p. 206—207 ℃ (Lit.6 208—211
℃). 1H NMR (CDCl3, 400 MHz) δ: 8.19—8.17 (m, 2H,
ArH), 8.06 (s, 1H, NH), 7.52—7.49 (m, 2H, ArH), 5.00
(s, 1H, NH), 5.52 (s, 1H, CH), 4.11 (q, J＝7.0 Hz, 2H,
CH2O), 2.36 (s, 3H, CH3), 1.19 (t, J＝7.0 Hz, 3H, CH3).
HRMS calcd for C14H15N3O5 (M＋) 305.1012, found
305.1023 (M＋, 19.25).
4e Yield 85%, m.p. 207—209 ℃ (Lit.11b 209—211
1
℃). H NMR (CDCl3, 400 MHz) δ: 7.88 (s, 1H, NH),
2026
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Chin. J. Chem. 2010, 28, 2025— 2032

Gallium (III) Iodide-catalyzed Biginelli-type Reaction Under Solvent-free Conditions
(DMSO-d6, 100 MHz) δ: 28.1, 28.2, 56.6, 79.1, 115.6,
118.6, 128.3, 128.4, 128.5, 129.4, 130.3, 131.9, 135.9,
136.5, 139.9, 142.1, 152.9.
that 10 mol% GaI3 was the best choice (Scheme 1, Table
1, Entries 7—9).
5c Yield 85%, m.p. 280—283 ℃ (Lit.22b 281—282
℃). 1H NMR (DMSO-d6, 400 MHz) δ: 8.87 (s, 1H, NH),
8.35—8.19 (m, 4H, ArH), 7.65—7.39 (m, 4H, ArH),
6.89—6.77 (m, 2H, NH＋CH), 5.39 (s, 1H, CH), 2.91—
2.86 (m, 2H, CH2), 2.26—2.18 (m, 1H, CH), 2.05—2.01
(m, 1H, CH). HRMS calcd for C20H16N4O5 (M ＋ )
392.1121, found 392.1121 (M＋, 83.64).
Scheme 1
5d Yield 81%, m.p. 238—240 ℃ (Lit.22a 238—241
℃). 1H NMR (DMSO-d6, 400 MHz) δ: 9.00 (s, 1H, NH),
7.41—7.26 (m, 9H, ArH＋CH), 6.92 (s, 1H, NH), 5.20
(s, 1H, CH), 2.84—2.83 (m, 2H, CH2), 2.45—2.37 (m,
1H, CH), 2.09 (s, 7H, 2×CH3＋CH). HRMS calcd for
C22H22N2O (M ＋ ) 330.1732, found 330.1723 (M ＋ ,
57.81).
Table 1 Effects of reaction conditions on the typical Biginelli
reaction catalyzed by GaI3
5e Yield 88%, m.p. 250—252 ℃ (Lit.22a 250—252
℃). 1H NMR (DMSO-d6, 300 MHz) δ: 8.64 (s, 1H, NH),
7.30—7.22 (m, 2H, ArH), 7.20—7.14 (m, 2H, ArH),
7.06 (s, 1H, ArH), 6.96—6.88 (m, 4H, ArH), 6.56 (s, 1H,
NH), 5.08 (s, 1H, CH), 3.75 (s, 6H, 2×OCH3), 2.77 (s,
2H, CH2), 2.38—2.33 (m, 1H, CH), 2.02—1.96 (m, 1H,
CH). HRMS calcd for C22H22N2O3 (M＋ ) 362.1630,
found 362.1626 (M＋, 100).
Entrya
Solvent
THF
GaI3/mol%
Time/h Yieldd/%
1
2
3
4
5
6
7
8
10
10
10
10
10
10
10
5
12b
12b
12b
12b
12b
12b
0.5c
1c
trace
trace
56
CH2Cl2
CH3CN
C6H6
Toluene
EtOH
—
31
5f Yield 86%, m.p. 260 — 264 ℃. 1H NMR
(DMSO-d6, 300 MHz) δ: 9.19 (s, 1H, NH), 8.38—6.74
(m, 15H, ArH＋CH), 6.04 (s, 1H, NH), 5.28 (s, 1H, CH),
2.79—2.71 (m, 2H, CH2), 2.43—2.41 (m, 1H, CH), 1.81
—1.73 (m, 1H, CH). 13C NMR (DMSO-d6, 100 MHz) δ:
27.6, 27.7, 55.87, 112.2, 118.7, 121.9, 122.7, 123.8,
124.0, 124.5, 124.8, 125.1, 125.6, 125.9, 127.2, 127.7,
127.9, 128.0, 129.6, 130.8, 132.8, 133.5, 135.5, 137.4,
138.4, 140.1, 153.0, 156.7. HRMS calcd for C28H22N2O
(M＋) 402.1732, found 402.1737 (M＋, 10.60).
29
82
95
—
72
9
—
15
0.5c
94
a
Benzaldehyde (1 mmol), ethyl acetoacetate (1 mmol), urea (1.2
mmol), GaI3 (10 mol%) were used in 3 mL mentioned solvent.
b Reflux. c 100 ℃. d Isolated yield.
5g Yield 89%, m.p. 286 — 288 ℃. 1H NMR
(DMSO-d6, 400 MHz) δ: 9.01 (s, 1H, NH), 7.41—7.24
(m, 11H, ArH＋CH), 6.92 (s, 1H, NH), 5.21 (s, 1H, CH),
2.84—2.83 (m, 2H, CH2), 2.43—2.42 (m, 1H, CH), 2.10
— 2.06 (m, 5H, CH ＋ 2CH2). HRMS calcd for
C22H22N2O (M ＋ ) 330.1732, found 330.1736 (M ＋ ,
15.30).
The reactions of a series of aryl and alkyl aldehydes,
ethyl acetoacetate and urea were performed under the
optimized conditions (Table 1, Entry 7). As seen in the
Table 2 and Scheme 2, all the reactions were finished in
1 h, and gave the good to excellent yields (79%—95%).
The results showed that the different aromatic aldehydes
(Table 2, Entries 1—7), aliphatic aldehydes (Table 2,
Entries 8—9), α,β-unsaturated aldehyde (Table 2, Entry
10) were all good substrates for the Biginelli reaction
catalyzed by 10 mol% GaI3. When thiourea was used
instead of urea, the expected product 4k was obtained in
90% yield (Table 2, Entry 11).
Results and discussion
Initially, we explored the typical Biginelli reaction of
ethyl acetoacetate, benzaldehyde and urea in DCM or
THF in the presence of 10 mol% GaI3, unfortunately,
trace product was obtained (Table 1, Entries 1, 2). Then,
the different solvents such as CH3CN, benzene, toluene
and EtOH were scanned (Table 1, Entries 3—6), in
which EtOH gave the 82% yield in 12 h (Table 1, Entry
6). Furthermore, the same reaction was conducted under
the solvent free condition, interestingly, its yield
reached to 95% and the reaction was completed in 0.5 h
(Table 1, Entry 7), which might be attributed to the high
concentration effect.24,25 Finally, the effect of catalyst
loading on the reaction was also investigated, showing
Scheme 2
Chin. J. Chem. 2010, 28, 2025— 2032
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Li et al.
FULL PAPER
Table 2 GaI3 catalyzed the Biginelli-type reaction under solvent-free conditiona
Entry
Aldehyde
Time/h
Yieldb/%
Productc
1
0.3
95
4a
2
3
4
5
6
7
8
0.5
90
91
90
85
92
79
84
4b
0.3
4c
0.25
0.75
0.5
4d
4e
4f
0.5
4g
CH3CHO
0.5
4h
2028
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Chin. J. Chem. 2010, 28, 2025— 2032

Gallium (III) Iodide-catalyzed Biginelli-type Reaction Under Solvent-free Conditions
Continued
Entry
9
Aldehyde
Time/h
1
Yieldb/%
Productc
82
4i
4j
10
11
0.5
0.5
87
90
4k
12
0.5
90
5a
13
0.75
83
5b
14
0.25
85
5c
15
0.75
81
5d
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Li et al.
FULL PAPER
Continued
Entry
Aldehyde
Time/h
Yieldb/%
Productc
16
0.5
88
5e
17
1
86
5f
18
1
89
5g
a
Aldehyde (1 mmol), ethyl acetoacetate (or cycloketone) (1 mmol), urea (1.2 mmol) and 10 mol% GaI3 were used under solvent-free
condition at 100 ℃. b Isolated yield. c All compounds were characterized by 1H NMR and HRMS analyses.
The above good results prompted us to extend the
substrates to cycloketones, fortunately, the reaction of
cyclopentanone, benzaldehyde and urea catalyzed by 10
mol% GaI3 yielded the expected product 5a in 90%
yield (Scheme 3, Table 2, Entry 12), which was charac-
yield (Table 2, Entry 17). However, when using cyclo-
hexanone instead of cyclopentanone, to our surprise, the
resultant was complicated. Interestingly, in case of
cyclohepanone the expected product 5g was afforded in
89% yield (Table 2, Entry 18). The reason of the differ-
ence for cycloketones is unknown. As seen the plausible
mechanism in Scheme 4, complex 6 added to imine 7 to
form intermediate 8, followed by cyclization and dehy-
dration to yield product 4a. Scheme 5 showed that two
molecules of imine 7 reacted with complex 10 derived
from cyclopentanone and GaI3 in situ, to yield interme-
diate 11, followed by cyclization and leaving one mole-
cule of H2O and urea to afford product 5a.26-28
1
terized by H NMR and HRMS analyses. Subsequently,
other aromatic aldehydes bearing either electron-
donating or electron-withdrawing substituents were used
for the reaction, and it was found that the electron effect
of substituents had little impact on the yield, all the re-
action gave the good yields (81—90%, Scheme 3, Table
2, Entries 12—16) without any by-product observed.
More hindered 1-naphthaldehyde was also conducted
for the reaction, giving the expected product 5f in 86%
Conclusion
Scheme 3
In conclusion, 10 mol% GaI3 can effectively catalyze
the Biginelli reaction of ethyl acetoacetate/cycloketone,
aldehyde and urea/thiourea under solvent-free condition
at 100 ℃. This work provided a new alternative way to
dihydropyrimidine-2(1H)-ones in good to excellent
yields, and our developed method has the advantages of
environmental benignity, simple workup, and easy
preparation of catalyst.
2030
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Chin. J. Chem. 2010, 28, 2025— 2032

Gallium (III) Iodide-catalyzed Biginelli-type Reaction Under Solvent-free Conditions
Scheme 4
Scheme 5
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