Copper-catalyzed coupling reaction of arylhydrazines and trialkylphosphites

Article abstract of DOI:10.1021/jo4022474

A novel CuO-catalyzed coupling reaction of arylhydrazines with trialkyl phosphites to afford arylphosphonates is described. The reaction proceeded at 80 C in air without external reductants, oxidants, and ligands.

Full text of DOI:10.1021/jo4022474

Note
pubs.acs.org/joc
Copper-Catalyzed Coupling Reaction of Arylhydrazines and
Trialkylphosphites
Sheng-Yan Chen,† Run-Sheng Zeng,*,† Jian-Ping Zou,*,†,‡ and Olayinka Taiwo Asekun§
†Key Laboratory of Organic Synthesis of Jiangsu Province, College of Chemistry, Chemical Engineering and Material Science,
Soochow University, Suzhou 215123, People’s Republic of China
‡Key Laboratory of Synthetic Chemistry of Natural Substances, Shanghai Institute of Organic Chemistry, Chinese Academy of
Sciences, Shanghai 200032, People’s Republic of China
§Department of Chemistry, University of Lagos, Akoka, Yaba, Nigeria
S
* Supporting Information
ABSTRACT: A novel CuO-catalyzed coupling reaction of arylhydrazines with trialkyl phosphites
to afford arylphosphonates is described. The reaction proceeded at 80 °C in air without external
reductants, oxidants, and ligands.
arbon−phosphorus bond formation is a current topic in
organic chemistry.1 The Michaelis−Arbuzov reaction is a
(Table 1, entry 2). Followed by screening different ligands such
as proline (L2), 2,2′-bipyridine (L3), 2,2′-bis(diphenylphos-
phino)-1,1′-binaphthyl (L4), N,N′-dimethylethylenediamine
(L5), PPh3 (L6), and 2,2′-biimidazole (L7) (Figure 1 and
Table 1, entries 4−9), the results showed that L7 works well for
the reaction (Table 1, entry 9). Occasionally, we found that the
reaction could also work in the absence of any ligand; however,
in the presence of Cu(OAc)2, the yield was reduced to 57%
(Table 1, entry 10). Interestingly, in the case of CuO/ligand-
free conditions, the reaction gave 3a in 71% yield (Table 1,
entry 11), which is higher than the yields of products
synthesized in the presence of ligands L1, L6, and L7 (Table
1, entries 3, 8, and 9). Among the different inorganic and
organic bases employed for the reaction, Cs2CO3 was the best
(Table 1, entries 11−15). Polar solvents such as CH3CN,
DMSO, DMF, and 1,4-dioxane and a representative nonpolar
solvent, toluene, were explored, and CH3CN led to the highest
yield (Table 1, entries 11 and 16−19). The catalytic activity of
Cu(I) and Cu(II) salts such as CuI, CuCl, CuBr, CuCl2, and
Cu(OAc)2 were investigated; they all catalyzed this reaction in
air, and CuO gave the best yield (Table 1, entries 11 and 20−
23). Other than the above-mentioned factors, the effects of
catalyst loading and reaction temperature and time were also
investigated, and the optimal reaction conditions were
determined to be 10 mol % CuO as catalyst and Cs2CO3 as
base in CH3CN at 80 °C for 24 h in air (Table 1, entries 24−
30).
C
well-known method for C−P bond formation; however, it is
not applicable to the formation of aryl C−P bonds.2 Therefore,
during the past 3 decades, great efforts have been focused on
the metal-catalyzed cross-coupling reactions of functionalized
arenes with phosphorus reagents. Until now, aryl halides,3
triflates,4a imidazolylsulfonates,4b diazonium salts,4c arylboronic
acids or aryltrifluoroborates,4d,e and o-aryl silyl triflates4f have
been used for the reaction catalyzed/promoted by Pd, Cu, Ni,
and CsF reagents to construct C(sp2)−P bonds (Scheme 1,
Scheme 1
path I). As part of our research on the C−P bond formation
catalyzed/promoted by copper or manganese reagents,5 this
note reports the first example of a coupling reaction of
phenylhydrazine with trimethylphosphite catalyzed by CuO
(Scheme 1, path II).
When the model reaction of phenylhydrazine (1a) with
trimethylphosphite (2a) was performed in refluxing CH3CN in
the presence only of inorganic base Cs2CO3, no reaction took
place. After addition of 10 mol % CuO and 1,10-phenanthrolin
(L1) as ligand, the reaction proceeded smoothly to afford the
desired product dimethyl phenylphosphonate (3a) in 46% yield
With the promising results obtained in the model reaction,
we then examined the substrate scope of arylhydrazines under
the optimized reaction conditions (10 mol % CuO as catalyst
and Cs2CO3 as base in CH3CN at 80 °C for 24 h in air). As
seen in Table 2, electron-donating substituents such as alkyl
Received: October 24, 2013
Published: January 27, 2014
© 2014 American Chemical Society
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The Journal of Organic Chemistry
Note
a
in Table 2, arylhydrazines (1) with ortho substituents such as
methyl, ethyl, Cl, and NO2 groups all suppressed the reaction
(Table 2, entries 2, 14, 16, 17, 18, and 19). With more bulky
ortho substituents, the yield became lower (Table 2, entries 2,
17, and 19), and when NO2 or two ethyl groups occupied one
or two ortho positions, the reaction was hindered (Table 2,
entries 16 and 18). Triethylphosphite and triphenylphosphite
were also applied to the reaction with 4-methoxyphenylhy-
drazine, and the results indicated that the former gave the
expected product in 68% yield, whereas the latter afforded a
trace product (Table 2, entries 20 and 21).
The plausible mechanism for the CuO-catalyzed coupling
reaction of arylhydrazines and trimethylphosphite is proposed
in Scheme 2. Cu(II) species are first reduced to Cu(I) by
trimethylphosphite (2) in situ; then, the aryl radical (4)
generated from arylhydrazines (1) oxidized by air (O2)6 and
trimethylphosphite (2) combine with Cu(I) species to form a
Cu(III) complex (5). The arylphosphonates (3) are produced
through the formation of a Cu(III) complex (6) via a CH3
radical leaving followed by a ligand-coupling reaction.
We extended this method to use different substituents on the
hydrazines such as sulfonyl, acyl, and alkyl hydrazines;
regretfully, the expected results were not obtained (Table 3,
entries 1−3).
Table 1. Optimization of the Reaction Conditions
b
entry
catalyst
CuO
solvent
base
ligand yield (%)
c
1
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
DMSO
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
N.D.
2
L1
L1
L2
L3
L4
L5
L6
L7
46
3
Cu(OAc)2
CuO
CuO
CuO
CuO
CuO
CuO
Cu(OAc)2
CuO
CuO
CuO
CuO
CuO
CuO
CuO
CuO
CuO
CuI
62
4
35
5
43
6
24
7
46
8
62
9
69
10
11
12
13
14
15
16
17
18
19
20
21
22
23
57
71
42
K2CO3
trace
57
N(Et)3
KOH
trace
<10
<10
62
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
DMF
In conclusion, a novel method for carbon−phosphorus bond
formation was developed through the coupling reaction of
arylhydrazines with trialkylphosphites catalyzed by 10 mol %
CuO. The reaction proceeded under mild conditions in air
without external reductants, oxidants, and ligands. Commer-
cially available Cu(II) and Cu(I) salts could all catalyze this
reaction, but the real catalytic species should be Cu(I). This
methodology provides an effective and cheap way to the
synthesis of arylphosphonates.
11,4-dioxane
toluene
21
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
55
CuBr
CuCl
CuCl2
CuO
CuO
CuO
CuO
CuO
CuO
CuO
47
51
59
d
24
28
e
25
62
f
26
67
g
27
39
EXPERIMENTAL SECTION
■
h
28
60
1
General Information. H and 13CNMR spectra were recorded in
i
29
68
CDCl3 (internal standard at 7.26 ppm for H and 77.5 ppm for 13C)
1
j
30
71
using a 300 or 400 MHz spectrometer. HRMS data were recorded on
a TOF instrument using the ESI technique. Column chromatography
was performed with 300−400 mesh silica gel using flash column
techniques. All of the reagents were used directly as obtained
commercially unless otherwise noted.
a
Reaction conditions: 1a (1.0 mmol), 2a (2.0 mmol), base (3.0
mmol), L (10 mol %), and catalyst (10 mol %) in CH3CN (3.0 mL) at
b
c
d
80 °C for 24 h in air. Isolated yields. N.D., not detected. Using 1
e
f
g
mol % CuO. Using 5 mol % CuO. Using 20 mol % CuO. At 25 °C.
h
i
j
General Procedure for the Preparation of Compound 3.
Arylhydrazine or its salt (1 mmol), trimethylphosphite (248 mg, 2
mmol), and Cs2CO3 (978 mg, 3 mmol) were added to a flask with
CH3CN (3 mL), the mixture was stirred for 15 min at room
temperature in air, and CuO (8.0 mg, 0.1 mmol) was then added. After
the reaction mixture was stirred at 80 °C for 24 h in air, it was allowed
to cool to room temperature, diluted with diethyl ether (5 mL), and
filtered, and the filtrate was concentrated under vacuum. The residue
was purified by column chromatography on silica gel (petroleum
ether/ethyl acetate 4:1 to 2:1) to afford desired pure product 3.
Dimethyl Phenylphosphonate (3a). Yellow oil (133.0 mg, 71%
yield). 1H NMR (CDCl3, 400 MHz): δ 7.90−7.70 (m, 2H), 7.67−7.52
(m, 1H), 7.51−7.40 (m, 2H), 3.77 (d, J = 11.2 Hz, 6H). 13C NMR (75
MHz, CDCl3): δ 133.1, 132.2 (d, J = 9.8 Hz), 129.0 (d, J = 14.9 Hz),
127.3 (d, J = 180.4 Hz), 53.0 (d, J = 5.4 Hz). MS (ESI-TOF) m/z: (M
+ 1)+ calcd for C8H12O3P, 187; found, 187.7
At 60 °C. At 100 °C. For 36 h.
Figure 1. Structure of the ligands.
Dimethyl o-Tolylphosphonate (3b). Yellow oil (129.3 mg, 58%
yield). H NMR (CDCl3, 300 MHz): δ 7.89 (dd, J = 6.0, 10.8 Hz,
and methoxy groups on the aryl ring of arylhydrazines (1)
facilitated the reaction to afford the arylphosphonates (3) in
moderate to good yields (Table 2, entries 3−7). On the
contrary, electron-withdrawing groups such as F, Cl, Br,
COOCH3, CN, and NO2 were unfavorable for the reaction
and led to lower yields (Table 2, entries 8−16). The role of the
ortho substituents for the reaction was then probed. As shown
1
1H), 7.50−7.40 (m, 1H), 7.30−7.10 (m, 2H), 3.76 (d, J = 8.4 Hz,
6H), 2.56 (s, 3H). 13C NMR (75 MHz, CDCl3): δ 142.3 (d, J = 10.0
Hz), 134.4 (d, J = 10.0 Hz), 133.1 (d, J = 3.0 Hz), 131.6 (d, J = 15.0
Hz), 126.1 (d, J = 185.0 Hz), 125.8 (d, J = 15.0 Hz), 52.8 (d, J = 6.0
Hz), 21.5 (d, J = 4.0 Hz). HRMS (ESI-TOF) m/z: (M + Na)+ calcd
for C9H13NaO3P, 223.0495; found, 223.0491.
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Note
a
Table 2. CuO-Catalyzed Coupling Reaction of Arylhydrazines and Trimethylphosphite
a
Reaction conditions: 1 (1.0 mmol), 2 (2.0 mmol), Cs2CO3 (3.0 mmol), and CuO (10 mol %) in CH3CN (3.0 mL) at 80 °C for 24 h in air.
Isolated yield. 4-Methoxyphenylhydrazine (1.0 and 8.0 mmol) afforded product 3d in 78 and 71% yield, respectively. Detected by LC−MS.
b
c
d
e
N.D., not detected.
Dimethyl p-Tolylphosphonate (3c). Yellow oil (140.0 mg, 70%
yield). 1H NMR (CDCl3, 300 MHz): δ 7.69 (dd, J = 6.0, 9.9 Hz, 2H),
7.35−7.20 (m, 2H), 3.74 (d, J = 11.2 Hz, 6H), 2.41 (s, 3H). 13C NMR
(75 MHz, CDCl3): δ 143.7, 132.3(d, J = 10.2 Hz), 129.7 (d, J = 15.4
Hz), 123.9 (d, J = 142.4 Hz), 52.9 (d, J = 5.2 Hz), 22.0. MS (ESI-
TOF) m/z: (M + 1)+ calcd for C9H14O3P, 201; found, 201.7
Dimethyl (4-Isopropylphenyl)phosphonate (3e). Yellow oil
(167.2 mg, 73% yield). H NMR (CDCl3, 400 MHz): δ 7.72 (dd, J =
1
8.0, 13.2 Hz, 2H), 7.50−7.30 (m, 2H), 3.75 (d, J = 10.8 Hz, 6H),
3.00−2.90 (m, 1H), 1.26 (d, J = 2.8 Hz, 6H). 13C NMR (75 MHz,
CDCl3): δ 154.3, 132.3 (d, J = 7.9 Hz), 127.1 (d, J = 15.4 Hz), 124.5
(d, J = 182.2 Hz), 52.9 (d, J = 8.3 Hz), 34.6, 23.9. HRMS (MALDI-
TOF) m/z: (M + 1)+ calcd for C11H18O3P, 229.0995; found,
229.0988.
Dimethyl (4-Methoxyphenyl)phosphonate (3d). Yellow oil
1
(168.2 mg, 78% yield). H NMR (CDCl3, 300 MHz): δ 7.74 (dd, J =
8.7, 12.9 Hz, 2H), 6.98 (dd, J = 3.3, 8.7 Hz, 2H), 3.86 (s, 3H), 3.74 (d,
J = 11.1 Hz, 6H). 13C NMR (75 MHz, CDCl3): δ 163.6, 134.3 (d, J =
8.5 Hz), 118.5 (d, J = 146.2 Hz), 114.6 (d, J = 10.5 Hz), 55.7, 52.9 (d,
J = 3.8 Hz). MS (ESI-TOF) m/z: (M + 1)+ calcd for C9H14O4P, 217;
found, 217.7
Dimethyl (4-tert-Butylphenyl)phosphonate (3f). Yellow oil
(175.0 mg, 72% yield). H NMR (CDCl3, 400 MHz): δ 7.73 (dd, J =
8.4, 13.2 Hz, 2H), 7.53−7.40 (m, 2H), 3.75 (d, J = 11.2 Hz, 6H), 1.33
(s, 9H). 13C NMR (75 MHz, CDCl3): δ 156.5, 132.0 (d, J = 10.2 Hz),
125.8 (d, J = 15.0 Hz), 123.4 (d, J = 189.9 Hz), 52.8 (d, J = 5.2 Hz),
1
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The Journal of Organic Chemistry
Note
TOF) m/z: (M + 1)+ calcd for C8H11ClO3P, 221.0129; found,
221.0129.
Scheme 2. Plausible Catalytic Mechanism
Dimethyl (4-Bromophenyl)phosphonate (3j). Yellow oil
1
(108.2 mg, 41% yield). H NMR (CDCl3, 400 MHz): δ 7.90−7.70
(m, 2H), 7.60−7.40 (m, 2H), 3.77 (d, J = 5.9 Hz, 6H). 13C NMR (75
MHz, CDCl3): δ 133.2, 132.3 (d, J = 9.8 Hz), 129.0 (d, J = 15.6 Hz),
127.4 (d, J = 187.6 Hz), 53.2 (d, J = 5.3 Hz). HRMS (ESI-TOF) m/z:
(M + 1)+ calcd for C8H11BrO3P, 264.9629; found, 264.9632.
Dimethyl (4-Methoxycarbonyl)phosphonate (3k). Yellow oil
1
(112.3 mg, 46% yield). H NMR (CDCl3, 400 MHz): δ 8.14 (dd, J =
10.0, 4.0 Hz, 2H), 7.89 (dd, J = 12.8, 8.40 Hz, 2H), 3.95 (s, 3H), 3.79
(d, J = 11.2 Hz, 6H). 13C NMR (75 MHz, CDCl3): δ 166.2, 133.8 (d, J
= 2.4 Hz), 131.9 (d, J = 7.5 Hz), 131.8 (d, J = 139.7 Hz), 129.5 (d, J =
11.3 Hz), 52.9 (d, J = 4.2 Hz), 52.5. HRMS (ESI-TOF) m/z: (M + 1)+
calcd for C10H14O5P, 245.0579; found, 245.0579.
Dimethyl (4-Nitrophenyl)phosphonate (3m). Yellow oil (88.1
1
mg, 38% yield). H NMR (CDCl3, 400 MHz): δ 7.65−7.50 (m, 2H),
6.80−6.60 (m, 2H), 3.71 (d, J = 13.3 Hz, 6H). 13C NMR (75 MHz,
CDCl3): δ 133.1, 132.3 (d, J = 9.7 Hz), 129.0 (d, J = 14.9 Hz), 127.3
(d, J = 187.9 Hz), 53.0 (d, J = 5.5 Hz). HRMS (ESI-TOF) m/z: (M +
1)+ calcd for C8H11NO5P, 232.0369; found, 232.0374.
Dimethyl (3-Chlorophenyl)phosphonate (3o). Yellow oil (79.5
1
mg, 36% yield). H NMR (CDCl3, 400 MHz): δ 7.15 (t, J = 8.0 Hz,
Table 3. CuO-Catalyzed Coupling Reaction of Sulfonyl,
Acyl, and Alkyl Hydrazines with Trimethylphosphite
a
1H), 6.90−6.80 (m, 1H), 6.70 (d, J = 1.6 Hz, 1H), 6.59 (d, J = 8.0 Hz,
1H), 3.73 (s, 3H), 3.23 (s, 3H). 13C NMR (100 MHz, CDCl3): δ
136.7 (d, J = 154.6 Hz), 130.9, 125.4, 121.3, 113.2, 111.5, 53.9. HRMS
(ESI-TOF) m/z: (M + 1)+ calcd for C8H11ClO3P, 221.0129; found,
221.0127.
Dimethyl (2-Ethylphenyl)phosphonate (3q). Yellow oil (49.2
mg, 23% yield). 1H NMR (CDCl3, 400 MHz): δ 7.88 (dd, J = 16.0, 7.6
Hz, 1H), 7.49 (dd, J = 8.0, 7.2 Hz, 1H), 7.34 (dd, J = 8.0, 6.6 Hz, 1H),
7.30−7.20 (m, 1H), 3.77 (d, J = 10.8 Hz, 6H), 2.96 (q, J = 7.6, 2H),
1.26 (t, J = 7.6, 3H). 13C NMR (75 MHz, CDCl3): δ 148.4 (d, J = 8.4
Hz), 134.0 (d, J = 7.6 Hz), 132.8 (d, J = 2.2 Hz), 129.6 (d, J = 11.3
Hz), 125.4 (d, J = 11.1 Hz), 125.0 (d, J = 137.8 Hz), 52.5 (d, J = 4.3
Hz), 27.2 (d, J = 2.8 Hz), 15.6. HRMS (ESI-TOF) m/z: (M + 1)+
calcd for C10H16O3P, 215.0837; found, 215.0837.
Diethyl (4-Methoxyphenyl)phosphonate (3t). Yellow oil
1
(165.9 mg, 68% yield). H NMR (CDCl3, 400 MHz): δ 7.76 (dd, J
= 12.0, 8.8 Hz, 2H), 7.10−6.89 (m, 2H), 4.26−3.96 (m, 2H, CH2),
3.85 (s, 3H, CH3), 1.32 (t, J = 7.2 Hz, 3H). 13C NMR (75 MHz,
CDCl3): δ 163.2 (d, J = 2.6 Hz), 134.1 (d, J = 8.5 Hz), 119.8 (d, J =
145.1 Hz), 114.4 (d, J = 11.9 Hz), 62.3 (d, J = 3.8 Hz), 55.7 (d, J = 2.0
Hz), 16.7 (d, J = 4.9 Hz). MS (ESI-TOF) m/z: (M + 1)+ calcd for
C11H18O4P, 245; found, 245.8
a
Reaction conditions: 1 (1.0 mmol), 2 (2.0 mmol), Cs2CO3(3.0
mmol), and CuO (10 mol %) in CH3CN (3.0 mL) at 80 °C for 24 h
in air. N.D., not detected.
b
ASSOCIATED CONTENT
■
S
* Supporting Information
1H and 13C NMR spectra of all of the products. This material is
available free of charge via the Internet at http://pubs.acs.org.
35.3, 31.3. HRMS (ESI-TOF) m/z: (M + 1)+ calcd for C12H20O3P,
243.1145; found, 243.1144.
Dimethyl (3,5-Dimethylphenyl)phosphonate (3g). Yellow oil
(158.2 mg, 67% yield). H NMR (CDCl3, 400 MHz): δ 7.41 (d, J =
1
AUTHOR INFORMATION
Corresponding Authors
*E-mail: zengrunsheng@suda.edu.cn (R.-S.Z.).
*E-mail: jpzou@suda.edu.cn (J.-P.Z.).
Notes
■
13.3 Hz, 2H), 7.19 (s, 1H), 3.75 (d, J = 11.2 Hz, 6H), 2.35 (s, 6H).
13C NMR (75 MHz, CDCl3): δ 138.6 (d, J = 13.5 Hz), 134.7 (d, J =
2.3 Hz), 129.7 (d, J = 9.7 Hz), 126.6 (d, J = 185.8 Hz), 52.9 (d, J = 5.3
Hz), 21.4. HRMS (ESI-TOF) m/z: (M + Na)+ calcd for
C10H15NaO3P, 237.0651; found, 237.0652.
The authors declare no competing financial interest.
Dimethyl (4-Fluorophenyl)phosphonate (3h). Yellow oil (86.1
1
mg, 42% yield). H NMR (CDCl3, 400 MHz): δ 7.90−7.70 (m, 2H),
7.21−7.10 (m, 2H), 3.77 (dd, J = 2.0, 11.6 Hz, 6H). 13C NMR (75
MHz, CDCl3): δ 165.6 (dd, J = 4.9, 251.4 Hz), 134.9 (dd, J = 9.1, 11.1
Hz), 123.6 (dd, J = 3.5, 193.2 Hz), 116.3 (dd, J = 16.3, 21.3 Hz), 53.1
(d, J = 7.3 Hz). MS (ESI-TOF) m/z: (M + 1)+ calcd for C8H11FO3P,
205; found, 205 .7
ACKNOWLEDGMENTS
■
We thank the National Natural Science Foundation of China
(nos. 20772088 and 21172163) and a project funded by the
Priority Academic Program Development of Jiangsu Higher
Education Institutions for funding this work.
Dimethyl(4-Chlorophenyl)phosphonate (3i). Yellow oil (101.2
1
mg, 46% yield). H NMR (CDCl3, 400 MHz): δ 7.71−7.60 (m, 2H),
7.45−7.30 (m, 2H), 3.68 (d, J = 10.0 Hz, 6H). 13C NMR (75 MHz,
CDCl3): δ 139.6 (d, J = 6.4 Hz), 133.6 (d, J = 14.2 Hz), 129.2 (d, J =
3.9 Hz), 126.2 (d, J = 190.7 Hz), 53.0 (d, J = 5.5 Hz). HRMS (ESI-
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