A palladium-catalyzed oxidative cross-coupling reaction between aryl pinacol boronates and H-phosphonates in ethanol

Article abstract of DOI:10.1039/c7ra04619g

The first successful oxidative coupling reaction of aryl pinacol boronic esters with H-phosphonates to deliver aryl phosphorous compounds is reported herein. These reactions between aryl boronic reagents and H-phosphonates were carried out synergistically using a Pd catalyst, additive and oxidant. Without using bases and ligands, phosphorylation was accomplished in an environmentally-friendly manner under mild conditions in ethanol.

Full text of DOI:10.1039/c7ra04619g

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A palladium-catalyzed oxidative cross-coupling
reaction between aryl pinacol boronates and
H-phosphonates in ethanol†
Cite this: RSC Adv., 2017, 7, 30214
*
Te-Hsuan Chen,‡ Daggula Mallikarjuna Reddy‡ and Chin-Fa Lee
The first successful oxidative coupling reaction of aryl pinacol boronic esters with H-phosphonates to
deliver aryl phosphorous compounds is reported herein. These reactions between aryl boronic reagents
and H-phosphonates were carried out synergistically using a Pd catalyst, additive and oxidant. Without
using bases and ligands, phosphorylation was accomplished in an environmentally-friendly manner
under mild conditions in ethanol.
Received 25th April 2017
Accepted 27th May 2017
DOI: 10.1039/c7ra04619g
rsc.li/rsc-advances
esters exhibit greater chemical stability and readily soluble in
aprotic solvents. In most cases, they also exhibit stability
Introduction
towards column chromatography, which aids in their ease of
isolation and purication. In addition, many are liquids at
room temperature and can be easily distilled. However, to the
best of our knowledge, the preparation of arylphosphorus
compounds via oxidative cross coupling reactions of aryl
boronic esters with H-phosphonates has never been developed.
Herein, we report the rst coupling reaction of aryl pinacol
boronic esters with H-phosphonates through palladium catal-
ysis (Scheme 1d). The features of this system include that the
reactions are performed in ethanol and also declined the
requirement of external ligand and base. The most important
feature that we observed was that the reaction conditions used
The development of versatile methods for the synthesis of
arylphosphorous compounds1 has attracted much attention,
owing to their broad applications in medicinal chemistry,2
materials chemistry,3 organic synthesis4 and catalysis.5 In 1981,
Hirao and co-workers reported the rst construction of C(sp2)–P
bonds through palladium-catalyzed cross-coupling of aryl
halides with H-phosphonates.6 During the past three decades,
the scope of the reactions catalyzed by Pd, Cu and Ni or other
metals reagents to form C(sp2)–P bonds employing functional-
ized arenes with phosphorus reagents has been signicantly
expanded to various aryl halides,7 triates,8 imidazolylsulfo-
nates,9 diazonium salts,10 o-aryl silyl triates,11 arylhydrazines,12
arylnitriles,13 aryl pivalates,14 sodium arylsulnates15 and dia-
ryliodonium salts.16 Arylphosphorus compounds can also be
produced by the palladium or copper-catalyzed directed C–H/
P(O)–H coupling reactions.17
Aryl boronic acids18 are extensively used as substrates in
transition-metal catalyzed cross-coupling reactions including
Suzuki–Miyaura cross-coupling reactions,19 Cu-catalyzed C–O,
C–N, C–S and C–Se coupling reactions,20 and Rh-catalyzed
conjugate additions to carbonyl compounds,21 owing to their
commercial availability and structural diversity. There are only
a few examples reported for C–P bond forming reactions using
aryl boronic acids (Scheme 1a–c).22 Notably, additional ligands
and bases are required in these works. Aryl boronic esters,
especially aryl pinacol boronates, have received a great deal of
attention in the catalysis community. In general, aryl boronic
Department of Chemistry, National Chung Hsing University, Taichung, Taiwan 402,
Republic of China. E-mail: cfalee@dragon.nchu.edu.tw; Fax: +886-4-2286-2547; Tel:
+886-4-2284-0411 ext. 810
† Electronic supplementary information (ESI) available: For 1H and 13C spectra of
componunds 3. See DOI: 10.1039/c7ra04619g
Scheme 1 Synthesis of aryl phosphorous compounds from arylbor-
‡ Both authors contributed equally to this work.
onic reagents.
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in Scheme 1a–c were not successful for the coupling of aryl yield of product in the presence of TMAC was because of its
pinacol boronate with H-phosphonate.
phase transfer catalytic and inert counter ionic nature. The yield
of the product was decreased to 32% when the reaction was
conducted with tert-butanol as the solvent (entry 11). The choice
of oxidant was crucial in this coupling reaction. When we
replaced Ag2CO3 with AgOAc and Cu(OAc)2, both led to 3aa at
lower yields (entries 12 and 14); meanwhile, no reaction
occurred when K2S2O8 or oxygen (ballon) was used as the
oxidant (entries 13 and 15). The superiority of Ag2CO3 over other
oxidants in this reaction could explained by its additional basic
nature that can promote the deprotonation of H-phosphonates.
In the screening of the palladium source, Pd(PPh3)2Cl2,
Pd(OCOCF3)2 and PdCl2 showed lower reactivity (entries 16–18)
compared with Pd(OAc)2.
We next investigated the relative reactivity of phenyl boronic
acid derivatives (Table 2). When phenyl boronic acid (4) was
used as a boron reagent, the coupling product 3aa was obtained
at 61% yield. Phenyl boronic esters, such as phenyl hexylene
glycol boronate (5) and phenyl neopentyl glycol boronate (6),
were also tested, but both gave the product at lower yields when
compared with phenyl pinacol boronate (2a).
With the optimized protocol from previous works, we
examined the scope of the substrates in this catalytic system
(Table 3). Various aryl pinacol boronates 2 were found to couple
with 1a to produce the corresponding diethyl arylphosphonates
3 at moderate to good yields. It is worth mentioning that higher
yields of products were obtained with aryl pinacol boronates 2
bearing electron-donating groups. Thus, with electron-donating
substituents such as methyl and methoxy groups at the C-3 or C-
4 position of 2, one could obtain the corresponding products at
good yields (3aa–3ag). In contrast, substrates with electron-
withdrawing triuoromethyl and chloro groups led to prod-
ucts at lower yields (3ah and 3ai). When we used 3-bromophenyl
Results and discussion
We selected diethyl phosphite (1a) and phenyl pinacol boronate
(2a) as model substrates to optimize the reaction conditions
(Table 1). Initially, the reaction was carried out with Pd(OAc)2 (5
mol%) as the catalyst and Ag2CO3 (1.5 equiv.) as the oxidant in
DMF at 80 ꢀC for 24 h; however, only a trace amount of the
desired product diethyl phenylphosphonate 3aa was detected
(entry 1). No product or only a trace amount of the product was
observed when DMSO, CH3CN or toluene was used as the
solvent (entries 2–4). To our delight, when the solvent was
changed to ethanol, the coupling product 3aa was obtained at
22% yield (entry 5). Key role of ethanol in this coupling reaction
to obtain the desired product can be explained by the possible
coordination of ethanol at boron centre of aryl pinacol boro-
nate. Due to the co-ordination of ethanol with aryl pinacol
boronate the electron density at aryl system may be increased.
When we chose tetramethylammonium bromide (TMAB), tet-
ramethylammonium chloride (TMAC), LiCl, CsCl and TBACl as
the additives, the coupling product 3aa with TMAC and LiCl
obtained 76% and 75% yields, respectively (entries 7 and 9),
whereas other additives gave inferior results. To our delight, we
chose TMAC as additive for this reaction. Enhancement of the
Table 1 Pd-catalyzed coupling of PhB(pin) with diethyl phosphitea
Table 2 Phosphorylation: relative reactivity of boron sourcesa
Entry
Additive
Oxidant
Solvent
Yieldb (%)
1
2
3
4
5
6
7
8
—
—
—
—
Ag2CO3
Ag2CO3
Ag2CO3
Ag2CO3
Ag2CO3
Ag2CO3
Ag2CO3
Ag2CO3
Ag2CO3
Ag2CO3
Ag2CO3
AgOAc
K2S2O8
Cu(OAc)2
O2
DMF
Trace
0
Trace
Trace
22
25
76
50
75
35
32
35
N.R.
28
N.R.
64
62
DMSO
CH3CN
Toluene
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
t-BuOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
—
TMAB
TMAC
CsCl
LiCl
TBAC
TMAC
TMAC
TMAC
TMAC
TMAC
TMAC
TMAC
TMAC
9
10
11
12
13
14
15
16c
17d
18e
Ag2CO3
Ag2CO3
Ag2CO3
65
a
a
Reaction conditions: 0.5 mmol of 1a, 1.5 equivalent of Ph[B], 5 mol%
Reaction conditions: 1a (0.5 mmol), 2a (1.5 eq.), Pd(OAc)2 (5 mol%),
Pd(OAc)2, 1.5 equivalent of TMACl, 1.5 equivalent of Ag2CO3, and 3 mL
of ethanol were charged into a Schlenk tube under nitrogen atmosphere
and heated at 80 ꢀC for 24 h.
additive (1.5 eq.), oxidant (1.5 eq.), and solvent (3.0 mL) under an
b
c
atmosphere of N2 for 24 h at 80 ꢀC. Isolated yield. Pd(PPh3)2Cl2 as
the catalyst. d Pd(OCOCF3)2 as the catalyst. e PdCl2 as the catalyst.
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Table 3 Substrate scope of aryl pinacol boronatesa
Table 4 Pd-catalyzed coupling of aryl pinacol boronates 2 with
phosphitesa
a
Reaction conditions: 0.5 mmol of 1, 1.5 equivalent of boronate 2, 5
mol% Pd(OAc)2, 1.5 equivalent of TMACl, 1.5 equivalent of Ag2CO3,
and 3 mL of ethanol were charged into a Schlenk tube under nitrogen
atmosphere and heated at 80 ꢀC for 24 h.
a
Reaction conditions: 0.5 mmol of 1a, 1.5 equivalent of boronates 2, 5
mol% Pd(OAc)2, 1.5 equivalent of TMACl, 1.5 equivalent of Ag2CO3, and
3 mL of ethanol were charged into a Schlenk tube under nitrogen
b
atmosphere and heated at 80 ꢀC for 24 h. Reaction at 70 ꢀC.
pinacol boronate as a coupling partner, the desired product was
obtained in trace amount along with de-brominated arylphosph-
onate (3aa) in lower yield. Use of various aryl pinacol boronic
esters such as 4-nitrophenyl, 4-methoxycarbonylphenyl, 4-cyano-
phenyl, naphthyl, 4-hydroxyphenyl pinacol boronates and heter-
oaryl pinacol boronates such as 3-thienyl, 5-indolyl pinacol
boronates as substrates to couple with H-phosphonate, failed to
the formation of desired products instead detected the de-
borolyted products. Furthermore, we also tested the reaction by
using ortho substituted aryl pinacol boronates such as 2-chlor-
ophenyl and mesityl pinacol boronates. Under the reaction
conditions, these two substrates also failed to react with H-phos-
phonate. The formation of de-borolyted product was detected by
GC analysis. Another important factor that was responsible for
lowering the yield of product was formation trialkylphosphates
by the reaction of H-phosphonate with solvent (ethanol).
Scheme 2 Plausible mechanism for the formation of 3.
this Pd-catalyzed cross-coupling takes place via the catalytic
cycle shown in Scheme 2. Firstly, the Pd(II) complex A reacted
with the phosphorous nucleophile generated by deprotona-
tion of the P(O)H compound in the presence of a Ag2CO3 to
provide intermediate B.22a,d The resulting intermediate B
associated with arylpinacol boronate (2) to give another
intermediate C,22a,d,23 which upon reductive elimination,
afforded the desired coupling product (3) and Pd(0) species.
Finally, the Pd(0) species was oxidized by Ag2CO3, leading to
the regeneration of Pd(II) complex A as a catalytically active
species.
The generality of this coupling reaction was further
demonstrated by using two other substituted phosphites,
dimethyl phosphite (1b) and dibutyl phosphite (1c). When
screening with different aryl pinacol boronates 2, both phos-
phites could produce the corresponding products at moderate
to good yields (Table 4).
Although the mechanism of this tranformation is not clear
at this stage, based on experimental results, we propose that
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(m, 2H), 4.05–4.19 (m, 4H), 1.33 (t, J ¼ 7.2 Hz, 3H), 1.32 (t, J ¼
7.2 Hz, 3H); 13C NMR (100 MHz, CDCl3): d 132.3 (d, JC–P ¼ 2.7
Hz), 131.7 (d, JC–P ¼ 9.9 Hz), 128.4 (d, JC–P ¼ 14.8 Hz), 128.2 (d,
JC–P ¼ 186.8 Hz), 62.0 (d, JC–P ¼ 5.3 Hz), 16.2 ((d, JC–P ¼ 6.4 Hz));
31P NMR (162 MHz, CDCl3): d 19.54.
Conclusion
In conclusion, we demonstrated a novel Pd-catalyzed cross-
coupling reaction of aryl pinacol boronates with H-phospho-
nates, which afforded good yields of arylphosphorus
compounds under mild conditions in ethanol. A variety of
readily available aryl pinacol boronates can be used in this
coupling reaction. We believe that this is a new protocol for the
construction of valuable C–P bonds from readily available,
environmentally friendly chemical sources.
Diethyl 4-methylphenylphosphonate (3ab):.22 Following the
general procedure for compound 3, using 4-methylphenylbor-
onic acid pinacol ester (163.6 mg, 0.75 mmol), Pd(OAc)2 (5.6 mg,
5 mol%), Ag2CO3 (0.21 g, 0.75 mmol) and tetramethylammo-
nium chloride (82 mg, 0.75 mmol) were added diethyl phos-
phite 1a (67.5 mL, 0.50 mmol) in ethanol (3.0 mL), then puried
by column chromatography (SiO2, ethyl acetate/hexane ¼ 30–
Experimental
General information
1
80%) to provide 3ab as a colorless oil (66.1 mg, 58% yield). H
NMR (400 MHz, CDCl3): d 7.72 (d, J ¼ 8.0 Hz, 1H), 7.69 (d, J ¼
8.0 Hz, 1H), 7.26–7.29 (m, 2H), 4.04–4.15 (m, 4H), 2.41 (s, 3H),
1.32 (t, J ¼ 7.2 Hz, 6H); 13C NMR (100 MHz, CDCl3): d 142.92 (d,
JC–P ¼ 3.1 Hz), 131.8 (d, JC–P ¼ 10.2 Hz), 129.2 (d, JC–P ¼ 15.5 Hz),
All commercial chemicals were used as received except where
noted. Aryl pinacol boronates were all prepared through litera-
ture procedures.24,25 Experiments were performed under a dini-
trogen atmosphere using standard Schlenk techniques unless
otherwise stated. Flash chromatography was performed on
Merck silica gel 60 (230–400 mesh).
124.8 (d, JC–P ¼ 189.0 Hz), 61.94 (d, JC–P ¼ 5.3 Hz), 21.6 (d, JC–P
¼
1.2 Hz), 16.26 (d, JC–P ¼ 6.5 Hz); 31P NMR (162 MHz, CDCl3):
d 20.21.
Diethyl 4-methoxyphenylphosphonate (3ac):.22 Following the
general procedure for compound 3, using 4-methox-
yphenylboronic acid pinacol ester (175.6 mg, 0.75 mmol),
Pd(OAc)2 (5.6 mg, 5 mol%), Ag2CO3 (0.21 g, 0.75 mmol) and
tetramethylammonium chloride (82 mg, 0.75 mmol) were
added diethyl phosphite 1a (67.5 mL, 0.50 mmol) in ethanol (3.0
mL), then puried by column chromatography (SiO2, ethyl
acetate/hexane ¼ 30–80%) to provide 3ac as a colorless oil
(80.5 mg, 66% yield). 1H NMR (400 MHz, CDCl3): d 7.77 (d, J ¼
8.8 Hz, 1H), 7.73 (d, J ¼ 8.8, 1H), 6.95–6.99 (m, 2H), 4.01–4.16
(m, 4H), 3.86 (s, 3H), 1.31 (t, J ¼ 7.2 Hz, 6H); 13C NMR (100 MHz,
CDCl3): d 162.8 (d, JC–P ¼ 3 Hz), 133.8 (d, JC–P ¼ 11.3 Hz), 119.4
(d, JC–P ¼ 193.5 Hz), 114.0 (d, JC–P ¼ 15.9 Hz), 61.9 (d, JC–P ¼ 4.9
Hz), 55.3, 16.3 (d, JC–P ¼ 6.4 Hz); 31P NMR (162 MHz, CDCl3):
d 20.78.
Analysis
NMR spectra were recorded on a Varian Unity Inova-600 or
a Varian Mercury-400 instrument using CDCl3 as a solvent.
Chemical shis are reported in parts per million (ppm) and
referenced to the residual solvent resonance. Coupling constant
(J) are reported in hertz (Hz). Standard abbreviations indicating
multiplicity were used as follows: s ¼ singlet, d ¼ doublet, t ¼
triplet, dd ¼ double doublet, q ¼ quartet, quin ¼ quintet, m ¼
multiplet, b ¼ broad. GC-MS analysis were performed on
a Agilent Technologies 5977A GC equipped with Agilent 7890B
MS. High-resolution mass spectra were carried out on a Jeol
JMS-HX 110 spectrometer by the services at the National Chung
Hsing University.
Diethyl 3-methylphenylphosphonate (3ad):.22 Following the
general procedure for compound 3, using 3-methylphenylbor-
General procedure for synthesis of compound 3
To a mixture of aryl pinacol boronic ester (0.75 mmol, 1.5 onic acid pinacol ester (163.6 mg, 0.75 mmol), Pd(OAc)2 (5.6 mg,
equiv.), Pd(OAc)2 (5.6 mg, 5 mol%), Ag2CO3 (0.21 g, 1.5 equiv.) 5 mol%), Ag2CO3 (0.21 g, 0.75 mmol) and tetramethylammo-
and tetramethylammonium chloride (82 mg, 1.5 equiv.) were nium chloride (82 mg, 0.75 mmol) were added diethyl phos-
added H-phosphonate (0.5 mmol) and ethanol (3.0 mL) under phite 1a (67.5 mL, 0.50 mmol) in ethanol (3.0 mL), then puried
nitrogen atmosphere. The resulting suspension was heated at by column chromatography (SiO2, ethyl acetate/hexane ¼ 30–
1
80 ꢀC for 24 h. Aer 24 h, the reaction mixture was cooled down 80%) to provide 3ad as a colorless oil (84.4 mg, 74% yield). H
to room temperature and diluted with ethyl acetate (20 mL). The NMR (400 MHz, CDCl3): d 7.57–7.66 (m, 2H), 7.30–7.37 (m, 2H),
resulting solution was directly ltered through a pad of celite 4.04–4.18 (m, 4H), 2.40 (s, 3H), 1.33 (t, J ¼ 7.2 Hz, 6H); 13C NMR
and the ltrate was concentrated under vacuum. The crude (100 MHz, CDCl3): d 138.2 (d, JC–P ¼ 14.8 Hz), 133.08 (d, JC–P
¼
product was puried by ash column chromatography (ethyl 3.1 Hz), 132.1 (d, JC–P ¼ 9.8 Hz), 128.5 (d, JC–P ¼ 34.2 Hz), 128.4
acetate/hexane ¼ 30–80/20–70).
(d, JC–P ¼ 40.2 Hz), 127.8 (d, JC–P ¼ 185.9 Hz), 61.9 (d, JC–P ¼ 5.3
Diethyl phenylphosphonate (3aa):.22 Following the general Hz), 21.2, 16.2 (d, JC–P ¼ 6.5 Hz); 31P NMR (162 MHz, CDCl3):
procedure for compound 3, using phenylboronic acid pinacol d 19.91.
ester 2a (153 mg, 0.75 mmol), Pd(OAc)2 (5.6 mg, 5 mol%),
Diethyl 3,5-dimethylphenylphosphonate (3ae):.12 Following
Ag2CO3 (0.21 g, 0.75 mmol) and tetramethylammonium chlo- the general procedure for compound 3, using 3,5-dimethyl-
ride (82 mg, 0.75 mmol) were added diethyl phosphite 1a (67.5 phenylboronic acid pinacol ester (174.1 mg, 0.75 mmol),
mL, 0.50 mmol) in ethanol (3.0 mL), then puried by column Pd(OAc)2 (5.6 mg, 5 mol%), Ag2CO3 (0.21 g, 0.75 mmol) and
chromatography (SiO2, ethyl acetate/hexane ¼ 30–80%) to tetramethylammonium chloride (82 mg, 0.75 mmol) were
provide 3aa as a colorless oil (81.3 mg, 76% yield). 1H NMR (400 added diethyl phosphite 1a (67.5 mL, 0.50 mmol) in ethanol (3.0
MHz, CDCl3): d 7.79–7.85 (m, 2H), 7.54–7.58 (m, 1H), 7.45–7.50 mL), then puried by column chromatography (SiO2, ethyl
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Diethyl 4-chlorophenylphosphonate (3ai):.12 Following the
general procedure for compound 3, using 4-chlorophenylbor-
onic acid pinacol ester (178.6 mg, 0.75 mmol), Pd(OAc)2 (5.6 mg,
5 mol%), Ag2CO3 (0.21 g, 0.75 mmol) and tetramethylammo-
nium chloride (82 mg, 0.75 mmol) were added diethyl phos-
phite 1a (67.5 mL, 0.50 mmol) in ethanol (3.0 mL), then puried
by column chromatography (SiO2, ethyl acetate/hexane ¼ 30–
acetate/hexane ¼ 30–80%) to provide 3ae as a colorless oil
(107.7 mg, 89% yield). 1H NMR (400 MHz, CDCl3): d 7.44 (s, 1H),
7.41 (s, 1H), 7.18 (s, 1H), 4.03–4.18 (m, 4H), 2.36 (s, 6H), 1.33* (t,
J ¼ 7.2 Hz, 3H), 1.32* (t, J ¼ 7.2 Hz, 3H); *This triplet was
merged with other triplet; 13C NMR (100 MHz, CDCl3): d 138.1
(d, JC–P ¼ 15.6 Hz), 134.1 (d, JC–P ¼ 3.0 Hz), 129.3 (d, JC–P ¼ 9.9
Hz), 127.6 (d, JC–P ¼ 185.2 Hz), 61.9 (d, JC–P ¼ 5.3 Hz), 21.1 (d, JC–
¼ 1.1 Hz), 16.2 (d, JC–P ¼ 6.8 Hz); 31P NMR (162 MHz, CDCl3):
1
80%) to provide 3ai as a colorless oil (33.5 mg, 27% yield). H
P
d 20.48.
NMR (400 MHz, CDCl3): d 7.77 (d, J ¼ 8.4 Hz, 1H), 7.73 (d, J ¼
8.8 Hz, 1H), 7.44–7.47 (m, 2H), 4.04–4.19 (m, 4H), 1.33 (t, J ¼
7.2 Hz, 6H); 13C NMR (100 MHz, CDCl3): d 138.9 (d, JC–P ¼ 3.8
Hz), 133.2 (d, JC–P ¼ 10.7 Hz), 128.8 (d, JC–P ¼ 15.6 Hz), 126.9 (d,
JC–P ¼ 190.1 Hz), 62.25 (d, JC–P ¼ 5.7 Hz), 16.3 (d, JC–P ¼ 6.4 Hz);
31P NMR (162 MHz, CDCl3): d 18.67.
Dimethyl phenylphosphonate (3ba):.22 Following the general
procedure for compound 3, using phenylboronic acid pinacol
ester (153 mg, 0.75 mmol), Pd(OAc)2 (5.6 mg, 5 mol%), Ag2CO3
(0.21 g, 0.75 mmol) and tetramethylammonium chloride
(82 mg, 0.75 mmol) were added dimethyl phosphite (46.7 mL,
0.50 mmol) in ethanol (3.0 mL), then puried by column
chromatography (SiO2, ethyl acetate/hexane ¼ 30–80%) to
provide 3ba as a colorless oil (49.3 mg, 53% yield). 1H NMR (400
MHz, CDCl3): d 7.78–7.84 (m, 2H), 7.56–7.60 (m, 1H), 7.46–7.51
(m, 2H), 3.78 (s, 3H), 3.75 (s, 3H); 13C NMR (100 MHz, CDCl3):
Diethyl (3-methoxy-5-methylphenyl)phosphonate (3af).
Following the general procedure for compound 3, using (3-
methoxy-5-methyl)phenyl boronic acid pinacol ester (186.1 mg,
0.75 mmol), Pd(OAc)2 (5.6 mg, 5 mol%), Ag2CO3 (0.21 g, 0.75
mmol) and tetramethylammonium chloride (82 mg, 0.75 mmol)
were added diethyl phosphite 1a (67.5 mL, 0.50 mmol) in
ethanol (3.0 mL), then puried by column chromatography
(SiO2, ethyl acetate/hexane ¼ 30–80%) to provide 3af as
a colorless oil (87.8 mg, 68% yield). 1H NMR (400 MHz, CDCl3):
d 7.21 (d, J ¼ 13.6 Hz, 1H), 7.13 (d, J ¼ 14.8 Hz, 1H), 6.90 (s, 1H),
4.18–4.04 (m, 4H), 3.82 (s, 3H), 2.37 (s, 3H), 1.33 (t, J ¼ 7.2 Hz,
6H); 13C NMR (100 MHz, CDCl3): d 159.3 (d, JC–P ¼ 20.1 Hz),
140.0 (d, JC–P ¼ 17.9 Hz), 128.9 (d, JC–P ¼ 185.2 Hz), 124.7 (d, JC–P
¼ 9.5 Hz), 119.4 (d, JC–P ¼ 3.0 Hz), 113.2 (d, JC–P ¼ 11.4 Hz), 62.0
(d, JC–P ¼ 4.9 Hz), 55.3, 21.3, 16.24 (d, JC–P ¼ 6.5 Hz); 31P NMR
(162 MHz, CDCl3): d 19.98; HRMS-EI calcd for C12H19O4P [M]+:
258.1021, found: 258.1028.
d 132.6 (d, JC–P ¼ 3.0 Hz), 131.8 (d, JC–P ¼ 9.9 Hz), 128.5 (d, JC–P
¼
15.2 Hz), 126.8 (d, JC–P ¼ 187.8 Hz), 52.6 (d, JC–P ¼ 5.7 Hz); 31P
NMR (162 MHz, CDCl3): d 22.33.
Diethyl 3,4-dimethylphenylphosphonate (3ag):.11 Following
the general procedure for compound 3, using 3,4-dimethyl-
phenylboronic acid pinacol ester (174.1 mg, 0.75 mmol),
Pd(OAc)2 (5.6 mg, 5 mol%), Ag2CO3 (0.21 g, 0.75 mmol) and
tetramethylammonium chloride (82 mg, 0.75 mmol) were
added diethyl phosphite 1a (67.5 mL, 0.50 mmol) in ethanol (3.0
mL), then puried by column chromatography (SiO2, ethyl
acetate/hexane ¼ 30–80%) to provide 3ag as a colorless oil
(87.2 mg, 72% yield). 1H NMR (400 MHz, CDCl3): d 7.50–7.61 (m,
2H), 7.21–7.28 (m, 1H), 4.02–4.17 (m 4H), 2.31 (s, 6H), 1.33 (t, J ¼
7.2 Hz, 3H), 1.32 (t, J ¼ 7.2 Hz, 3H); 13C NMR (100 MHz, CDCl3):
d 141.7 (d, JC–P ¼ 3.4 Hz), 137.0 (d, JC–P ¼ 15.2 Hz), 132.8 (d, JC–P
¼ 10.3 Hz), 129.6 (d, JC–P ¼ 45.9 Hz), 129.5 (d, JC–P ¼ 40.2 Hz),
125.1 (d, JC–P ¼ 187.8 Hz), 61.9 (d, JC–P ¼ 5.3 Hz), 19.9, 19.6, 16.3
(d, JC–P ¼ 6.8 Hz); 31P NMR (162 MHz, CDCl3): d 20.59.
Diethyl 4-triuoromethylmethylphenylphosphonate (3ah):.22
Following the general procedure for compound 3, using 4-tri-
uorophenylboronic acid pinacol ester (204.1 mg, 0.75 mmol),
Pd(OAc)2 (5.6 mg, 5 mol%), Ag2CO3 (0.21 g, 0.75 mmol) and
tetramethylammonium chloride (82 mg, 0.75 mmol) were
added diethyl phosphite 1a (67.5 mL, 0.50 mmol) in ethanol (3.0
mL), then puried by column chromatography (SiO2, ethyl
acetate/hexane ¼ 30–80%) to provide 3ah as a colorless oil
(25.4 mg, 18% yield). 1H NMR (400 MHz, CDCl3): d 7.97 (d, J ¼
7.6 Hz, 1H), 7.94 (d, J ¼ 8.0 Hz, 1H), 7.72–7.75 (m, 2H), 4.10–4.20
(m, 4H), 1.34 (t, J ¼ 6.8 Hz, 6H); 13C NMR (100 MHz, CDCl3):
d 134.0 (d, J ¼ 33.0 Hz), 132.7 (d, J ¼ 185.5 Hz), 132.2 (d, J ¼ 9.9
Hz), 125.3 (dq, J ¼ 15.1, 3.8 Hz), 123.5 (q, J ¼ 270.6 Hz), 62.5 (d, J
¼ 5.7 Hz), 16.3 (d, J ¼ 6.5 Hz); 31P NMR (162 MHz, CDCl3):
d 17.02; 19F NMR (376 MHz, CDCl3): d ꢁ63.3.
Dimethyl 3-methylphenylphosphonate (3bd). Following the
general procedure for compound 3, using 3-methylphenylbor-
onic acid pinacol ester (163.6 mg, 0.75 mmol), Pd(OAc)2 (5.6 mg,
5 mol%), Ag2CO3 (0.21 g, 0.75 mmol) and tetramethylammo-
nium chloride (82 mg, 0.75 mmol) were added dimethyl phos-
phite (46.7 mL, 0.50 mmol) in ethanol (3.0 mL), then puried by
column chromatography (SiO2, ethyl acetate/hexane ¼ 30–80%)
1
to provide 3bd as a colorless oil (48.0 mg, 48% yield). H NMR
(400 MHz, CDCl3): d 7.57–7.65 (m, 2H), 7.38 (b, 2H), 3.73–3.78
(m, 6H), 2.40 (s, 3H); 13C NMR (100 MHz, CDCl3): d 138.4 (d, JC–P
¼ 15.2 Hz), 133.4 (d, JC–P ¼ 3.1 Hz), 132.3 (d, JC–P ¼ 9.8 Hz), 128.7
(d, JC–P ¼ 39.1 Hz), 128.6 (d, JC–P ¼ 45.5 Hz), 126.5 (d, JC–P
¼
186.7 Hz), 52.6 (d, JC–P ¼ 5.3 Hz), 21.3; 31P NMR (162 MHz,
CDCl3): d 22.80; HRMS-EI calcd for C9H13O3P [M]+: 200.0602,
found: 200.0597.
Dibutyl phenylphosphonate (3ca):.11 Following the general
procedure for compound 3, using phenylboronic acid pinacol
ester 2a (153 mg, 0.75 mmol), Pd(OAc)2 (5.6 mg, 5 mol%),
Ag2CO3 (0.21 g, 0.75 mmol) and tetramethylammonium chlo-
ride (82 mg, 0.75 mmol) were added dibutyl phosphite (101.5
mL, 0.50 mmol) in ethanol (3.0 mL), then puried by column
chromatography (SiO2, ethyl acetate/hexane ¼ 20–70%) to
provide 3ca as a colorless oil (93.2 mg, 69% yield). 1H NMR (400
MHz, CDCl3): d 7.77–7.84 (m, 2H), 7.53–7.58 (m, 1H), 7.44–7.49
(m, 2H), 3.96–4.12 (m, 4H), 1.61–1.69 (m, 4H), 1.34–1.44 (m,
4H), 0.90 (t, J ¼ 7.2 Hz, 6H); 13C NMR (100 MHz, CDCl3): d 132.3,
131.7 (d, JC–P ¼ 9.1 Hz), 128.4 (d, JC–P ¼ 14.5 Hz), 128.3 (d, JC–P
¼
186.6 Hz), 65.7 (d, JC–P ¼ 5.4 Hz), 32.4 (d, JC–P ¼ 6.4 Hz), 18.7,
13.5; 31P NMR (162 MHz, CDCl3): d 19.36.
30218 | RSC Adv., 2017, 7, 30214–30220
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Dibutyl p-tolylphosphonate (3cb):.15 Following the general
RSC Advances
7.39 (s, 1H), 7.17 (s, 1H), 3.96–4.09 (m, 4H), 2.35 (s, 6H), 1.62–
1.70 (m, 4H), 1.36–1.43 (m, 4H), 0.91 (t, J ¼ 7.2, 6H); 13C NMR
procedure for compound 3, using p-tolylphenylboronic acid
pinacol ester (163.6 mg, 0.75 mmol), Pd(OAc)2 (5.6 mg, 5 mol%),
Ag2CO3 (0.21 g, 0.75 mmol) and tetramethylammonium chlo-
ride (82 mg, 0.75 mmol) were added dibutyl phosphite (101.5
mL, 0.50 mmol) in ethanol (3.0 mL), then puried by column
chromatography (SiO2, ethyl acetate/hexane ¼ 20–70%) to
provide 3cb as a colorless oil (86.7 mg, 61% yield). 1H NMR (400
MHz, CDCl3): d 7.72 (d, J ¼ 8.0 Hz, 1H), 7.68 (d, J ¼ 8.0 Hz, 1H),
7.25–7.29 (m, 2H), 3.96–4.09 (m, 4H), 2.40 (s, 3H), 1.65 (quin, J ¼
6.8 Hz, 4H), 1.34–1.44 (m, 4H), 0.90 (t, J ¼ 7.2, 6H); 13C NMR
(100 MHz, CDCl3): d 142.7 (d, JC–P ¼ 2.3 Hz), 131.6 (d, JC–P ¼ 10.2
Hz), 129.0 (d, JC–P ¼ 15.2 Hz), 124.7 (d, JC–P ¼ 189.4 Hz), 65.5 (d,
JC–P ¼ 5.7 Hz), 32.2 (d, JC–P ¼ 6.5 Hz), 21.4, 18.5, 13.4; 31P NMR
(162 MHz, CDCl3): d 20.09.
(100 MHz, CDCl3): d 138.0 (d, JC–P ¼ 15.4 Hz), 133.95 (d, JC–P
¼
2.7 Hz), 129.3 (d, JC–P ¼ 10 Hz), 127.8 (d, JC–P ¼ 184.8 Hz), 65.6
(d, JC–P ¼ 5.5 Hz), 32.4 (d, JC–P ¼ 7.3 Hz), 21.1, 18.6, 13.5; 31P
NMR (162 MHz, CDCl3): d 20.40; HRMS-EI calcd for C16H27O3P
[M]+: 298.1698, found: 298.1707.
Dibutyl (3-methoxy-5-methylphenyl)phosphonate (3cf).
Following the general procedure for compound 3, using (3-
methoxy-5-methyl)phenyl boronic acid pinacol ester (186.1 mg,
0.75 mmol), Pd(OAc)2 (5.6 mg, 5 mol%), Ag2CO3 (0.21 g, 0.75
mmol) and tetramethylammonium chloride (82 mg, 0.75 mmol)
were added dibutyl phosphite (101.5 mL, 0.50 mmol) in ethanol
(3.0 mL), then puried by column chromatography (SiO2, ethyl
acetate/hexane ¼ 20–70%) to provide 3cf as a colorless oil
(72.3 mg, 46% yield). 1H NMR (400 MHz, CDCl3): d 7.10–7.23 (m,
2H), 6.89 (s, 1H), 3.97–4.10 (m, 4H), 3.82 (s, 3H), 2.37 (s, 3H),
Dibutyl 4-methoxyphenylphosphonate (3cc):.26 Following the
general procedure for compound 3, using 4-methox-
yphenylboronic acid pinacol ester (175.6 mg, 0.75 mmol),
Pd(OAc)2 (5.6 mg, 5 mol%), Ag2CO3 (0.21 g, 0.75 mmol) and
tetramethylammonium chloride (82 mg, 0.75 mmol) were
added dibutyl phosphite (101.5 mL, 0.50 mmol) in ethanol (3.0
mL), then puried by column chromatography (SiO2, ethyl
acetate/hexane ¼ 20–70%) to provide 3cc as a colorless oil
(102.1 mg, 68% yield). 1H NMR (400 MHz, CDCl3): d 7.75 (d, J ¼
8.8 Hz, 1H), 7.72 (d, J ¼ 8.8 Hz, 1H), 6.95–6.99 (m, 2H), 3.94–4.07
(m, 4H), 3.85 (s, 3H), 1.60–1.68 (m, 4H), 1.35–1.44 (m, 4H), 0.90
1.62–1.70 (m, 4H), 1.35–1.45 (m, 4H), 0.91 (t, J ¼ 7.2 Hz, 6H); 13
C
NMR (100 MHz, CDCl3): d 159.4 (d, JC–P ¼ 19.8 Hz), 139.9 (d, JC–P
¼ 17.4 Hz), 129.0 (d, JC–P ¼ 185.2 Hz), 124.7 (d, JC–P ¼ 9.5 Hz),
119.4 (d, JC–P ¼ 3.4 Hz), 113.3 (d, JC–P ¼ 11 Hz), 65.75 (d, JC–P
¼
5.7 Hz), 55.3, 32.4 (d, JC–P ¼ 6.5 Hz), 21.31 (d, JC–P ¼ 1.5 Hz),
18.7, 13.5; 31P NMR (162 MHz, CDCl3): d 19.69; HRMS-EI calcd
for C16H27O4P [M]+: 314.1647, found: 314.1655.
Dibutyl 3,4-dimethylphenylphosphonate (3cg). Following
the general procedure for compound 3, using 3,4-dimethyl-
phenylboronic acid pinacol ester (174.1 mg, 0.75 mmol),
Pd(OAc)2 (5.6 mg, 5 mol%), Ag2CO3 (0.21 g, 0.75 mmol) and
tetramethylammonium chloride (82 mg, 0.75 mmol) were
added dibutyl phosphite (101.5 mL, 0.50 mmol) in ethanol (3.0
mL), then puried by column chromatography (SiO2, ethyl
acetate/hexane ¼ 20–70%) to provide 3cg as a colorless oil
(76.0 mg, 51% yield). 1H NMR (400 MHz, CDCl3): d 7.49–7.59 (m,
2H), 7.20–7.24 (m, 1H), 3.93–4.10 (m, 4H), 2.30 (s, 6H), 1.61–1.69
(m, 4H), 1.34–1.44 (m, 4H), 0.91 (t, J ¼ 7.2 Hz, 6H); 13C NMR (100
(t, J ¼ 7.2 Hz, 6H); 13C NMR (100 MHz, CDCl3): d 162.7 (d, JC–P
¼
2.8 Hz), 133.6 (d, JC–P ¼ 10.9 Hz), 119.3 (d, JC–P ¼ 192.9 Hz),
113.8 (d, JC–P ¼ 15.4 Hz), 65.5 (d, JC–P ¼ 5.4 Hz), 55.1, 32.3 (d, JC–P
¼ 6.3 Hz), 18.6, 13.4; 31P NMR (162 MHz, CDCl3): d 20.47;
HRMS-EI calcd for C15H25O4P [M]+: 300.1490, found: 300.1484.
Dibutyl 3-methylphenylphosphonate (3cd). Following the
general procedure for compound 3, using 3-methylphenylbor-
onic acid pinacol ester (163.6 mg, 0.75 mmol), Pd(OAc)2 (5.6 mg,
5 mol%), Ag2CO3 (0.21 g, 0.75 mmol) and tetramethylammo-
nium chloride (82 mg, 0.75 mmol) were added dibutyl phos-
phite (101.5 mL, 0.50 mmol) in ethanol (3.0 mL), then puried by
column chromatography (SiO2, ethyl acetate/hexane ¼ 20–70%)
MHz, CDCl3): d 141.6, 136.9 (d, JC–P ¼ 15.4 Hz), 132.8 (d, JC–P
¼
10.0 Hz), 129.6 (d, JC–P ¼ 43.7 Hz), 129.4 (d, JC–P ¼ 38.2 Hz),
125.2 (d, JC–P ¼ 188.4 Hz), 65.6 (d, JC–P ¼ 6.4 Hz), 32.4 (d, JC–P
¼
7.3 Hz), 19.9, 19.6, 18.7, 13.5; 31P NMR (162 MHz, CDCl3):
d 20.51; HRMS-EI calcd for C16H27O3P [M]+: 298.1698, found:
298.1700.
1
to provide 3cd as a colorless oil (78.1 mg, 55% yield). H NMR
(400 MHz, CDCl3): d 7.56–7.65 (m, 2H), 7.34–7.37 (m, 2H), 3.95–
4.11 (m, 4H), 2.40 (s, 3H), 1.62–1.70 (m, 4H), 1.34–1.45 (m, 4H),
0.91 (t, J ¼ 7.6 Hz, 6H); 13C NMR (100 MHz, CDCl3): d 138.1 (d,
JC–P ¼ 14.5 Hz), 133.0, 132.2 (d, JC–P ¼ 10 Hz), 128.5 (d, JC–P ¼ 40
Hz), 128.4 (d, JC–P ¼ 46.4 Hz), 128.0 (d, JC–P ¼ 187.5 Hz), 65.6 (d,
JC–P ¼ 5.5 Hz), 32.3 (d, JC–P ¼ 7.3 Hz), 21.2, 18.6, 13.5; 31P NMR
(162 MHz, CDCl3): d 19.91; HRMS-EI calcd for C15H25O3P [M]+:
284.1541, found: 284.1540.
Acknowledgements
The Ministry of Science and Technology, Taiwan (Most 105-
2113-M-005-001-) and the National Chung Hsing University are
gratefully acknowledged for nancial support.
Dibutyl 3,5-dimethylphenylphosphonate (3ce). Following
the general procedure for compound 3, using 3,5-dimethyl-
phenylboronic acid pinacol ester (174.1 mg, 0.75 mmol),
Pd(OAc)2 (5.6 mg, 5 mol%), Ag2CO3 (0.21 g, 0.75 mmol) and
tetramethylammonium chloride (82 mg, 0.75 mmol) were
added dibutyl phosphite (101.5 mL, 0.50 mmol) in ethanol (3.0
mL), then puried by column chromatography (SiO2, ethyl
acetate/hexane ¼ 20–70%) to provide 3ce as a colorless oil
(99.8 mg, 67% yield). 1H NMR (400 MHz, CDCl3): d 7.43 (s, 1H),
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