Solvent-free synthesis of alkylaminophenols via petasis Boronic Mannich reaction in one pot without catalysts

Article abstract of DOI:10.1002/cjoc.201090340

By using solvent-free and heat conditions, the Petasis boronic Mannich reaction of salicylaldehydes with various boronic acids and secondary amines without catalyst is described. The alkylaminophenols were obtained in moderate to good yields in a shorter

Full text of DOI:10.1002/cjoc.201090340

FULL PAPER
Solvent-free Synthesis of Alkylaminophenols via Petasis
Boronic Mannich Reaction in One Pot without Catalysts
Liu, Ying(刘影)
Wang, Limin*(王利民)
Sui, Yuanyuan(眭园园)
Yu, Jianjun(余建军)
Laboratory for Advanced Materials, Institute of Fine Chemicals, East China University of
Science and Technology, Shanghai 200237, China
By using solvent-free and heat conditions, the Petasis boronic Mannich reaction of salicylaldehydes with vari-
ous boronic acids and secondary amines without catalyst is described. The alkylaminophenols were obtained in
moderate to good yields in a shorter reaction time than the traditional methods.
Keywords solvent-free, Petasis boronic Mannich reaction, boronic acids, salicylaldehydes, amines, multicompo-
nent reactions
Introduction
Scheme 1 The Petasis boronic Mannich reaction between sali-
cylaldehydes, boronic acids and secondary amines
One-pot multicomponent reaction, which has been
used for the synthesis of combinatorial libraries, makes
the combination of several organic molecules easy and
gives access to high synthetic efficiency and molecular
diversity.1 The Petasis boronic Mannich reaction2
(Scheme 1) makes a significant contribution to the li-
brary construction of alkylaminophenol molecules.
Compounds of this class have gathered much attention
because of their accessibility to various reagents and
their potential applications in drug discovery, plant pro-
tection and material science. Of note, aldehydes pos-
sessing a coordinating group, such as glyoxylic acids
and salicylaldehydes, are commonly used. Additionally,
other reagents3,4 such as boronic esters,5 substituted hy-
drazines,6 indoles7 and heterocycle aldehydes,8 have
also been used for the Petasis reaction.
Most of the reported Petasis boronic Mannich reac-
tions were carried out in organic solvents such as
methanol, ethanol, dichloromethane, toluene, dioxane
and acetonitrile. In some cases, hexafluoroisopropanol,9
microwave irradiation10 and solid-phase synthesis11
were employed in this reaction. However, these proce-
dures required either a long reaction time or microwave
activation. The development of environmental friendly
protocol for the Petasis boronic Mannich reaction is
necessary. Yadav et al.12 reported the use of ionic liquid
to accelerate the Petasis reaction. Recently, Candeias
et al.13 reported that water was also a suitable medium
for this reaction, while this procedure needed reaction for
24 h. Performing organic synthesis under solvent-free
conditions is one of the most promising strategies. Herein,
we wish to report the Petasis reaction between boronic
acids, salicylaldehydes and secondary amines carried out
without catalyst under solvent-free and heat conditions.
Results and discussion
Initially, the reaction involving phenylboronic acid,
salicylaldehyde and morpholine was studied by using
solvent-free conditions (Scheme 2). As shown in Table
1, the corresponding product was obtained in 13% yield
after 6 h at room temperature. Then we studied the ef-
fect of reaction temperature. The results showed that the
yield increased with the rise of temperature (Table 1,
Scheme 2 The model Petasis boronic Mannich reaction between
phenyl boronic acid, salicylaldehyde and morpholine
*
E-mail: wanglimin@ecust.edu.cn; Tel.: 0086-021-64253881; Fax: 0086-021-64253881
Received April 23, 2010; revised May 27, 2010; accepted June 12, 2010.
Project supported by the National Natural Science Foundation of China (No. 20672035).
Chin. J. Chem. 2010, 28, 2039— 2044
© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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Liu et al.
FULL PAPER
Table 1 The effect of reaction time and temperature on the
tions with electron-rich secondary amines such as cyclic
amine, dibenzylamine and benzylmethylamine gave
good yields (80%—96%). However, diethylamine and
dibutylamine just gave moderate yields (51%, 45%
respectively, Table 2, Entries 6, 7).
model Petasis boronic Mannich reactiona
Entry
Time/h
Temperature/℃
Yieldb/%
13
1
2
3
4
5
6
7
8
9
6
6
r.t.
40
60
80
100
80
80
80
80
57
Furthermore, several para-substituted phenylboronic
acids were chosen to react with salicylaldehyde and
morpholine under solvent-free conditions to test the effect
of the substituents. Satisfactory yields were obtained with
many kinds of substituted phenyl or heteroaryl boronic
acids (Table 2, Entries 8—12). The boronic acids bear-
ing an electron-donating para-substituent in the phenyl
group were good for this reaction, which gave higher
yields (Table 2, Entries 10, 11) than the electron-
withdrawing substituted phenyl boronic acids. The
p-fluorophenylboronic acid gave the lowest yield.
4-Methyl, 4-methoxy phenyl boronic acid as well as
thiophenyl-3-boronic acid performed quite well. Addi-
tionally, when the 2-hydroxy-4-methyl-benzaldehyde or
3,5-di-tert-butylsalicylaldehyde was used (Table 2, En-
tries 14, 15), the yield showed a slightly decrease.
In conclusion, we have shown that the Petasis bo-
ronic Mannich reaction between aryl or heteroaryl bo-
ronic acids, salicylaldehydes and secondary amines
worked efficiently under solvent-free and heat condi-
tions. This procedure reduced the reaction time to 2 h
which was much shorter than traditional methodology
without using microwave. Various alkylaminophenols
were synthesized in moderate to good yields.
6
82
6
97
6
82
0.5
1
82
89
2
92
3
92
a Reagents: phenyl boronic acid (1.2 mmol), salicylaldehyde (1
mmol), morpholine (1.2 mmol). b Isolated yield.
Entries 1—4). To our delight, the yield increased to
97% at 80 ℃ after 6 h. While raising the temperature
over 80 ℃, the yield of this reaction decreased (Table 1,
Entry 5). Next, the reaction time was explored. It is
worthy to note that after 2 h the alkylaminophenol was
obtained in 92% yield. No significant improvement was
shown by prolonged time.
With the optimum conditions in hand, the protocol
was then extended to a range of aryl or heteroaryl bo-
ronic acids and secondary amines (Table 2). In most
cases, various secondary amines worked well in the
solvent-free Petasis boronic Mannich reactions. Reac-
Table 2 The scope of the Petasis boronic Mannich reaction under solvent-free conditions
Entry
1
Aldehyde
Boronic acid
Amine
Product
Yielda,b/%
92
1a
2a
3a
2
3
83
81
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Chin. J. Chem. 2010, 28, 2039— 2044

Solvent-free Synthesis of Alkylaminophenols via Petasis Boronic Mannich Reaction
Continued
Yielda,b/%
Entry
4
Aldehyde
Boronic acid
Amine
Product
80
85
4a
5
6
5a
51
6a
7a
7
8
45
89
91
95
94
8a
9
9a
10
11
10a
11a
Chin. J. Chem. 2010, 28, 2039— 2044
© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
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Liu et al.
FULL PAPER
Continued
Entry
Aldehyde
Boronic acid
Amine
Product
Yielda,b/%
12
96
89
86
12a
13
14
13a
14a
15
82
15a
a Reagents: boronic acid (1.2 mmol), salicylaldehyde (1mmol), secondary amines (1.2 mmol). b Isolated yield.
Experimental
2-[Morpholino(phenyl)methyl]phenol
(1a)10
White solid, m.p. 114—116 ℃ (Lit. 117—119 ℃),
EtOAc (analytical grade), boronic acids and salicy-
laldehyde were purchased from commercial suppliers
and used without further purification. Melting points
(uncorrected) were measured on a SGW X-4 micro-
1
yield 247 mg (92%); H NMR (CDCl3, 400 MHz) δ:
2.45—2.64 (m, 4H), 3.77—3.81 (m, 4H), 4.42 (s, 1H),
6.74 (t, J＝7.4 Hz, 1H), 6.88 (d, J＝8.0 Hz, 1H), 6.96 (d,
J＝7.2 Hz, 1H), 7.14 (t, J＝7.6 Hz, 1H), 7.25—7.34 (m,
3H), 7.44 (d, J＝6.4 Hz, 2H), 11.76 (s, 1H); 13C NMR
(CDCl3, 100 MHz) δ: 52.25, 66.91, 76.75, 117.05,
119.60, 124.81, 128.12, 128.70, 128.94, 129.40, 139.30,
156.12.
scopic melting point apparatus. H (400 MHz) and 13C
1
(100 MHz) NMR spectra were recorded on a Bruker
Avance 400 spectrometer in CDCl3 using TMS as an
internal standard. Mass spectra (EI) were recorded on a
Micromass GCTTM mass spectrometer. HRMS (ESI)
were recorded on a Micromass LCTTM mass spec-
trometer. Column chromatography was carried out using
300—400 mesh silica gel.
2-[Phenyl(pyrrolidin-1-yl)methyl]phenol
(2a)13
1
Yellow liquid, yield 211 mg (83%); H NMR (CDCl3,
400 MHz) δ: 1.82—1.89 (m, 4H), 2.52 (brs, 2H), 2.66
(brs, 2H), 4.39 (s, 1H), 6.72 (t, J＝7.4 Hz, 1H), 6.87 (d,
J＝8.0 Hz, 1H), 6.97 (d, J＝7.6 Hz, 1H), 7.11 (t, J＝7.8
Hz, 1H), 7.23—7.31 (m, 3H), 7.48 (d, J＝7.2 Hz, 2H);
13C NMR (CDCl3, 100 MHz) δ: 23.47, 53.21, 75.73,
116.87, 119.14, 126.69, 127.68, 127.78, 128.29, 128.35,
128.71, 142.12, 156.65.
General procedure for the Petasis boronic Mannich
reaction under solvent-free conditions
Boronic acid (1.2 mmol), salicylaldehyde (1 mmol),
and secondary amine (1.2 mmol) were mixed in a
Schlenk flask. The mixture was stirred at 80 ℃ for 2 h.
Then, after cooling to room temperature, the mixture
was dissolved in EtOAc (6 mL). The sequent suspension
was then filtered or washed with water. The filtrate or
oil phase was concentrated and the pure product was
isolated by column chromatography using EtOAc-
petroleum ether mixture as an eluent.
2-[Phenyl(piperidin-1-yl)methyl]phenol
(3a)
1
White solid, m.p. 86—88 ℃, yield 216 mg (81%); H
NMR (CDCl3, 400 MHz) δ: 1.49 (brs, 2H), 1.64—1.68
(m, 4H), 2.44 (brs, 4H), 4.50 (s, 1H), 6.71 (t, J＝7.4 Hz,
1H), 6.87 (d, J＝8.0 Hz, 1H), 6.91 (d, J＝7.6 Hz, 1H),
7.12 (t, J＝7.2 Hz, 1H), 7.29—7.34 (m, 3H), 7.41 (brs,
2042
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Chin. J. Chem. 2010, 28, 2039— 2044

Solvent-free Synthesis of Alkylaminophenols via Petasis Boronic Mannich Reaction
2H), 12.56 (s, 1H); 13C NMR (CDCl3, 100 MHz) δ:
24.12, 26.08, 29.70, 76.47, 116.85, 119.00, 125.54,
127.81, 128.31, 128.67, 128.83, 129.18, 139.44, 157.14;
MS m/z (%): 267 (M＋, 17.99), 181 (100); HRMS (ESI)
calcd for C18H22NO [M＋H]＋ 268.1701, found 268.1699.
2-[(Dibenzylamino)(phenyl)methyl]phenol (4a)10
White solid, m.p. 123—125 ℃, yield 303 mg (80%);
1H NMR (CDCl3, 400 MHz) δ: 3.46 (d, J＝13.2 Hz, 2H),
4.00 (d, J＝13.2 Hz, 2H), 5.19 (s, 1H), 6.76 (t, J＝7.4
Hz, 1H), 6.86 (d, J＝7.2 Hz, 1H), 7.00 (d, J＝8.0 Hz,
117.19, 119.72, 124.68, 128.85, 129.28, 130.17, 130.24,
135.19, 135.22, 155.96, 161.21, 163.67.
2-[(4-Bromophenyl)(morpholino)methyl]phenol
(9a) White solid, m.p. 99—101 ℃, yield 317 mg
1
(91%); H NMR (CDCl3, 400 MHz) δ: 2.44—2.60 (m,
4H), 3.76—3.78 (m, 4H), 4.38 (s, 1H), 6.75 (t, J＝7.4
Hz, 1H), 6.88 (d, J＝8.0 Hz, 1H), 6.93 (d, J＝7.2 Hz,
1H), 7.15 (t, J＝7.0 Hz, 1H), 7.33 (d, J＝8.0 Hz, 2H),
7.44 (d, J＝8.8 Hz, 2H), 11.54 (s, 1H); 13C NMR
(CDCl3, 100 MHz) δ: 52.27, 66.83, 76.20, 117.23,
1H), 7.22 (t, J＝7.6 Hz, 1H), 7.30—7.46 (m, 15H),
12.14 (s, 1H); 13C NMR (CDCl3, 100 MHz) δ: 53.80,
68.34, 116.73, 119.05, 124.55, 127.61, 128.26, 128.59,
128.64, 128.87, 129.67, 129.79, 130.60, 135.80, 136.94,
157.55.
119.78, 122.13, 124.30, 128.96, 129.23, 130.15, 132.12,
138.43, 155.92; MS m/z (%): 347 (M＋, 13.65), 18－1
(100); HRMS (ESI) calcd for C17H17NO2Br [M－H]
346.0443, found 346.0450.
2-[Morpholino(p-tolyl)methyl]phenol
(10a)13
2-[(N-Benzyl-N-methylamino)(phenyl)methyl]-
phenol (5a) Pale yellow solid, m.p. 79—82 ℃, yield
White solid, m.p. 111—113 ℃, yield 268 mg (95%);
1H NMR (CDCl3, 400 MHz) δ: 2.32 (s, 3H), 2.48—2.61
(m, 4H), 3.77—3.79 (m, 4H), 4.40 (s, 1H), 6.74 (t, J＝
7.4 Hz, 1H), 6.88 (d, J＝8.0 Hz, 1H), 6.96 (d, J＝7.6 Hz,
1H), 7.12—7.16 (m, 3H), 7.33 (d, J＝7.6 Hz, 2H), 11.79
(s, 1H); 13C NMR (CDCl3, 100 MHz) δ: 21.08, 52.17,
66.03, 76.50, 116.99, 119.59, 124.99, 128.45, 128.60,
129.36, 129.60, 136.26, 137.88, 156.11
1
256 mg (85%); H NMR (CDCl3, 400 MHz) δ: 2.19 (s,
3H), 3.58 (s, 2H), 4.73 (s, 1H), 6.74 (t, J＝7.6 Hz, 1H),
6.93 (t, J＝8.6 Hz, 1H), 7.16 (t, J＝8.2 Hz, 1H), 7.29—
7.39 (m, 9H), 7.50 (d, J＝7.6 Hz, 2H), 12.35 (s, 1H); 13C
NMR (CDCl3, 100 MHz) δ: 39.16, 59.64, 75.54, 116.99,
119.21, 125.41, 127.58, 128.10, 128.63, 128.69, 128.83,
129.01, 129.16, 129.31, 137.23, 138.86, 156.97; MS m/z
(%): 303 (M＋, 7.69), 181 (100); HRMS (ESI) calcd for
C21H22NO [M＋H]＋ 304.1701, found 304.1707.
2-[(4-Methoxyphenyl)(morpholino)methyl]-phenol
(11a)13 White solid, m.p. 104—106 ℃, yield 281 mg
1
(94%); H NMR (CDCl3, 400 MHz) δ: 2.44—2.59 (m,
2-[(Dibutylamino)(phenyl)methyl]phenol
(6a)
4H), 3.76—3.78 (m, 7H), 4.39 (s, 1H), 6.74 (t, J＝7.4
Hz, 1H), 6.86 (t, J＝9.4 Hz, 3H), 6.94 (d, J＝7.6 Hz,
1H), 7.13 (t, J＝7.6 Hz, 1H), 7.34 (d, J＝8.4 Hz, 2H),
11.79 (s, 1H); 13C NMR (CDCl3, 100 MHz) δ: 52.13,
55.21, 66.92, 76.05, 114.22, 117.00, 119.58, 125.11,
128.58, 129.34, 129.77, 131.30, 156.10, 159.36.
Pale yellow liquid, yield 157 mg (51%); 1H NMR
(CDCl3, 400 MHz) δ: 0.88 (t, J＝7.2 Hz, 6H), 1.21—
1.28 (m, 4H), 1.48—1.54 (m, 4H), 2.43—2.50 (m, 2H),
2.61—2.68 (m, 2H), 4.92 (s, 1H), 6.69 (t, J＝7.4 Hz,
1H), 6.80 (d, J＝7.2 Hz, 1H), 6.86 (d, J＝8.0 Hz, 1H),
7.14 (t, J＝7.6 Hz, 1H), 7.32 (d, J＝8.0 Hz, 2H), 7.48 (d,
J＝8.4 Hz, 2H), 12.43 (s, 1H); 13C NMR (CDCl3, 100
MHz) δ: 13.92, 20.55, 28.11, 49.65, 70.78, 116.90,
118.93, 121.88, 125.12, 128.64, 128.89, 130.95, 131.75,
137.60, 157.48; MS m/z (%): 311 (M＋, 1.41), 181 (100);
HRMS (ESI) calcd for C21H30NO [M＋H]＋ 312.2327,
found 312.2329.
2-[Morpholino(thiophen-3-yl)methyl]phenol (12a)
Pale yellow solid, m.p. 138—140 ℃, yield 265 mg
1
(96%); H NMR (CDCl3, 400 MHz) δ: 2.45—2.59 (m,
4H), 3.76—3.80 (m, 4H), 4.60 (s, 1H), 6.76 (t, J＝7.4
Hz, 1H), 6.88 (d, J＝8.4 Hz, 1H), 6.96 (d, J＝7.6 Hz,
1H), 7.13—7.21 (m, 2H), 7.27—7.29 (m, 2H), 11.58 (s,
1H); 13C NMR (CDCl3, 100 MHz) δ: 51.78, 66.91,
71.12, 116.95, 119.55, 123.70, 124.45, 126.72, 127.1＋9,
128.84, 129.19, 139.59, 156.15; MS m/z: 275 (M ,
15.37), 187 (100); HRMS (ESI) calcd for C15H18NO2S
[M＋H]＋ 276.1058, found 276.1052.
2-[(Diethylamino)(phenyl)methyl]phenol
(7a)
Pale yellow liquid, yield 114 mg (45%); 1H NMR
(CDCl3, 400 MHz) δ: 1.10 (t, J＝7.2 Hz, 6H), 2.55—
2.64 (m, 2H), 2.73—2.82 (m, 2H), 4.93 (s, 1H), 6.69 (t,
J＝7.4 Hz, 1H), 6.86 (d, J＝8.0 Hz, 2H), 7.13 (t, J＝7.6
Hz, 1H), 7.29—7.36 (m, 3H), 7.46 (d, J＝7.2 Hz, 2H);
13C NMR (CDCl3, 100 MHz) δ: 11.06, 42.89, 71.00,
116.79, 118.82, 125.74, 127.84, 128.35, 128.63, 129.06,
129.10, 138.85, 157.57; MS m/z (%): 255 (M＋, 7.60),
181 (100); HRMS (ESI) calcd for C17H22NO [M＋H]＋
256.1701, found 256.1693.
5-Methoxy-2-[morpholino(phenyl)methyl]phenol
(13a)13 White solid, m.p. 122—125 ℃, yield 267 mg
1
(89%); H NMR (CDCl3, 400 MHz) δ: 2.42—2.60 (m,
4H), 3.73—3.79 (m, 7H), 4.38 (s, 1H), 6.30 (dd, J＝8.6,
2.8 Hz, 1H), 6.43 (d, J＝2.8 Hz, 1H), 6.82 (d, J＝8.4 Hz,
1H), 7.25 (t, J＝3.4 Hz, 1H), 7.30 (t, J＝7.4 Hz, 2H),
7.39 (d, J＝6.8 Hz, 2H), 11.85 (s, 1H); 13C NMR
(CDCl3, 100 MHz) δ: 52.12, 55.20, 66.93, 76.25, 102.19,
105.87, 117.18, 128.03, 128.54, 128.90, 130.04, 139.46,
157.34, 160.29.
2-[(4-Fluorophenyl)(morpholino)metyl]phenol
(8a)13 White solid, m.p. 89—91 ℃, yield 255 mg
1
(89%); H NMR (CDCl3, 400 MHz) δ: 2.43—2.60 (m,
4H), 3.76—3.82 (m, 4H), 4.42 (s, 1H), 6.76 (t, J＝7.4
Hz, 1H), 6.89 (d, J＝8.4 Hz, 1H), 6.94 (d, J＝7.6 Hz,
1H), 7.01 (t, J＝6.8 Hz, 2H), 7.15 (t, J＝7.6 Hz, 1H),
7.41—7.44 (m, 4H), 11.64 (s, 1H); 13C NMR (CDCl3,
100 MHz) δ: 52.24, 66.86, 76.01, 115.73, 115.94,
5-Methyl-2-[morpholino(phenyl)methyl]phenol
(14a)13 White solid, m.p. 127—129 ℃, yield 244 mg
1
(86%); H NMR (CDCl3, 400 MHz) δ: 2.30 (s, 3H),
2.45—2.60 (m, 4H), 3.76—3.79 (m, 4H), 4.39 (s, 1H),
6.51—6.57 (m, 1H), 6.71 (d, J＝2.8 Hz, 1H), 6.86 (d,
Chin. J. Chem. 2010, 28, 2039— 2044
© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
2043

Liu et al.
Romanenko, V. D.; Kukhar, V. P. Synlett 2010, 1, 73.
(c) Follmann, M.; Graul, F.; Schäfer, T.; Kopec, S.; Hamley,
P. Synlett 2005, 6, 1009.
FULL PAPER
J＝8.0 Hz, 1H), 7.27 (t, J＝3.6 Hz, 1H), 7.31 (t, J＝7.6
Hz, 2H), 7.39 (d, J＝7.0 Hz, 2H), 11.66 (s, 1H); 13C
NMR (CDCl3, 100 MHz) δ: 21.18, 52.24, 66.95, 76.57,
117.63, 120.51, 121.90, 128.03, 128.49, 128.95, 129.26,
138.79, 139.58, 155.90.
4
5
(a) Prakash, G. K. S.; Mandal, M.; Schweizer, S.; Petasis, N.
A.; Olah, G. A. J. Org. Chem. 2002, 67, 3718.
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6922.
2,4-Di-tert-butyl-6-[morpholino(phenyl)methyl]-
phenol (15a) White solid, m.p. 102—105 ℃, yield
1
313 mg (82%); H NMR (CDCl3, 400 MHz) δ: 1.24 (s,
9H), 1.48 (s, 9H), 2.48—2.64 (m, 4H), 3.79 (s, 4H),
4.41 (s, 1H), 6.83 (s, 1H), 7.20 (s, 1H), 7.25—7.29 (m,
1H), 7.33 (t, J＝7.4 Hz, 2H), 7.50 (d, J＝5.6 Hz, 2H),
11.84 (s, 1H); 13C NMR (CDCl3, 100 MHz) δ: 29.60,
31.64, 34.13, 35.03, 52.18, 66.88, 77.70, 122.84, 123.79,
124.06, 127.83, 128.67, 128.83, 136.19, 139.79, 140.79,
152.58; HRMS (ESI) calcd for C25H36NO2 [M＋H]＋
382.2746, found 382.2752.
(b) Koolmeister, T.; Södergren, M.; Scobie, M. Tetrahedron
Lett. 2002, 43, 5969.
(c) Tremblay-Morin, J.-P.; Raeppel, S.; Gaudette, F. Tetra-
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