Cetyltrimethyl ammonium bromide catalysed oxidative cross dehydrogenative coupling of benzylic C(sp3)-H bonds in methylarenes with P(O)-OH compounds

Article abstract of DOI:10.1039/c8ob02772b

An efficient metal-free method for the synthesis of organophosphorus compounds via oxidative cross dehydrogenative coupling of benzylic C(sp³)-H bonds in methylarenes with P(O)-OH compounds catalysed by cetyltrimethyl ammonium bromide (CTAB) is

Full text of DOI:10.1039/c8ob02772b

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Cetyltrimethyl ammonium bromide catalysed
oxidative cross dehydrogenative coupling of
benzylic C(sp3)–H bonds in methylarenes with
P(O)–OH compounds†
Cite this: Org. Biomol. Chem., 2019,
17, 302
Hang Li,‡a Jian Lei,‡a Yongping Liu,b Yi Chen,*b Chak-Tong Auc and
a
Shuang-Feng Yin
*
An efficient metal-free method for the synthesis of organophosphorus compounds via oxidative cross
dehydrogenative coupling of benzylic C(sp3)–H bonds in methylarenes with P(O)–OH compounds cata-
lysed by cetyltrimethyl ammonium bromide (CTAB) is reported. Various methylarenes and P(O)–OH com-
pounds are tolerated in the reaction with moderate to good yields. Compared to previous studies, the
present study extends the substrate scope and adopts a new reaction system of an ammonium salt cata-
lyst (CTAB) and an oxidant (DTBP). The results of control and mechanistic experiments are generally in
agreement with the overall proposed pathway. This method circumvents the use of toxic P–halogen
reagents and P(O)–H compounds for the synthesis of organophosphorus compounds.
Received 7th November 2018,
Accepted 7th December 2018
DOI: 10.1039/c8ob02772b
rsc.li/obc
of compounds are found in numerous biological, pharma-
ceutical, and material substances.5–8 Traditionally, these com-
Introduction
Cetyltrimethyl ammonium bromide (CTAB) has been exten- pounds are prepared by nucleophilic substitution of toxic
sively investigated as a surface-active agent for a number of halides P(O)–X with alcohol or phenol derivatives.9,10 With the
decades and is widely used as a wetting agent in food chem- major advances of Atherton–Todd reactions, it appears that
istry and as an emulsifier and plasticizer in industrial proces- there is a clean and straightforward approach to construct
ses.1a–c Furthermore, this compound has received much atten- phosphate ester derivatives. For example, the direct catalytic
tion in the field of heterogeneous catalysis and biology;1d–f it is P(O)–H/Nu–H cross dehydrogenative coupling (CDC) strategy
used as a mesopore template in the preparation of catalysts2a–b that led to successful iodine-catalysed phosphorylation of alco-
as well as an agent to modify montmorillonite (MMT)3 and hols reported by Dhineshkumar and Prabhu,11 and the iron-
bentonite (ACMB).4 In contrast, the application of CTAB in catalysed dehydrogenative coupling of alcohols with P(O)–H
homogeneous catalysis is undisclosed. Herein, we report an compounds by Chen and Han.12 As another appealing option
efficient metal-free method for the synthesis of organo- for the synthesis of phosphate ester compounds, the direct
phosphorus compounds based on CTAB-catalysed oxidative P(O)–H/C–H cross dehydrogenative coupling should be an
cross dehydrogenative coupling of benzylic C(sp3)–H bonds in efficient approach. For instance, using unprocessed toluene
methylarenes with P(O)–OH compounds.
derivatives as starting substrates and tetrabutylammonium
The generation of organophosphorus compounds is of iodide (Bu4NI) as a catalyst, Tang and coworkers successfully
great importance in synthetic chemistry because these kinds synthesized phosphorus esters via phosphorylation of benzyl
C–H bonds.13 Despite the progress, the synthetic methods are
somewhat restricted by the prerequisite of substrates that are
aState Key Laboratory of Chemo/Biosensing and Chemometrics,
air and moisture sensitive. Therefore, continuous efforts have
College of Chemistry and Chemical Engineering, Hunan University,
been made to circumvent this hurdle. Most recently, through
Changsha 410082, China. E-mail: sf_yin@hnu.edu.cn
C(sp3)–H bond phosphorylation of methyl-substituted arenes
using Bu4NI as a catalyst, Xiong et al. expanded the metal-free
synthetic process to relatively inexpensive and stable sub-
strates, namely, diarylphosphinic acids.14 Nevertheless, this
method is only compatible with aryl phosphinic acids and
compounds that contain primary C(sp3)–H, and the cross
coupling of inert phosphoric diesters and non-primary
bSchool of Medicine, Hunan University of Chinese Medicine, Changsha 410208,
PR China. E-mail: cscy1975@163.com
cCollege of Chemistry and Chemical Engineering, Hunan Institute of Engineering,
Xiangtan, 411104, P. R. China
†Electronic supplementary information (ESI) available: General information,
experimental procedures, and copies of 1H, 31P and 13C NMR spectra of pro-
ducts. See DOI: 10.1039/c8ob02772b
‡These authors contributed equally.
302 | Org. Biomol. Chem., 2019, 17, 302–308
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benzylic C(sp3)–H based on this method was found unsatisfac- loading were also studied (Table 1, entries 25–27). Ultimately,
tory. Hence, the development of an efficient metal-free method the optimal reaction conditions are as follows: diphenyl-
that is diversely substrate-tolerant for the synthesis of organo- phosphinic acid (0.1 mmol), toluene (0.5 ml), DTBP (4 equiv.)
phosphorus compounds via oxidative C–H/P(O)OH cross dehy- and CTAB (20 mol%) at 120 °C for 10 h under a nitrogen
drogenative coupling is highly desired.
atmosphere.
With the optimized conditions in hand, we turned to
explore other kinds of substrates (Table 2). A variety of func-
tional groups such as methyl (3b–3e), fluoro (3f), chloro
(3g and 3h), bromo (3i), iodo (3j), phenyl (3k), and methoxyl
(3l) are well-tolerated under the standard conditions. It is
noted that steric methylnaphthalenes (3m and 3n) and inert
2-methylquinoline (3o) are compatible, giving the corres-
ponding products in moderate to good yields. In the cases of
mesitylene (3e), p-cymene (3p) and 1-(tert-butyl)-4-methyl-
benzene (3q), the reaction exclusively occurs at the primary
benzylic C(sp3)–H bond. In addition, the substrates without a
primary benzylic C(sp3)–H bond, such as ethylbenzene (3r),
diphenylmethane (3s) and 1,2-diphenylethane (3t), are found
suitable for this reaction. Overall, the results indicate that the
protocol has circumvented the limitations of the previously
reported methods.13 Moreover, the reaction works well for an
array of phosphoric diesters. For instance, diethyl hydrogen
phosphate and dibutyl hydrogen phosphate react smoothly
with numerous toluene derivatives bearing either electron-
donating or electron-withdrawing groups as in the cases of
methylnaphthalenes (4f and 4i). The presence of steric hin-
drance has little effect on the efficiency of the reaction, as
illustrated in the cases of 4f and 4i.
Results and discussion
Our initial investigation centred on the use of oxidizing
reagents for the generation of suitable radical species.
Diphenylphosphinic acid and toluene were employed as start-
ing reagents. Also serving as a solvent, the latter was kept in
excess. Various oxidizing reagents, such as TBHP, DCP, TBPB,
BPO, DDQ, DTBP and H2O2, were tested (Table 1, entries 1–7).
Among them, DTBP was found to be the best, and to
monitor its usage, its amount was varied from 4 equiv. to 0.5
equiv. (Table 1, entries 15–17). Furthermore, it was observed
that the yield of 3a is temperature dependent (Table 1, entries
7–11). To optimize the reaction conditions and to widen the
application of the strategy, other catalysts and solvents were
evaluated (Table 1, entries 19–24). The effects of catalyst
Table 1 Optimization of reaction conditions
In order to gain insight into the reaction mechanism,
control experiments were performed (see the ESI† for details).
To begin with, benzyl alcohol, benzyl aldehyde or benzyl
bromide was assumed to be a potential intermediate in the
reaction. Nonetheless, replacing toluene with benzyl alcohol,
benzyl aldehyde or benzyl bromide did not yield the desired
product (Scheme 1a), contradicting the possibility that benzyl
alcohol, benzyl aldehyde or benzyl bromide is an intermediate
in this reaction. When a radical scavenger, such as 2,2,6,6-
tetramethylpiperidine N-oxyl (TEMPO), 2,6-di-tert-butyl-4-
methylphenol (BHT) or 1,4-benzoquinone (BQ), was added
into the reaction of 1a with toluene under the optimal con-
ditions, there was no generation of the desired product
(Scheme 1b). The phenomenon confirms the involvement of
radicals in this reaction. Finally, an intermolecular compe-
tition experiment between toluene and toluene-d8 was per-
formed, with kH/kD values up to 1.6 (Scheme 1c), indicating
that hydrogen abstraction of toluene is rate-determining in
this reaction.
According to the above results, we deduce that the reaction
is initiated by CTAB and DTBP through the formation of
benzyl radicals. Furthermore, on the basis of the results
reported by Shi and coworkers,15a,b we speculate that during
the reaction the benzyl radicals are oxidized to benzyl cations.
Based on the above criteria, a plausible catalytic cycle is pro-
posed as presented in Scheme 2. Initially, the reaction between
CTAB and DTBP gives the active intermediate ammonium 6
([(C19H42)N]+[BrO]−) or 7 ([(C19H42)N]+[BrO2]−) that is able to
Entry
Catalyst
Oxidant
Solvent
Yield (%)
1
2
3
4
CTAB (20 mol%)
CTAB (20 mol%)
CTAB (20 mol%)
CTAB (20 mol%)
CTAB (20 mol%)
CTAB (20 mol%)
CTAB (20 mol%)
CTAB (20 mol%)
CTAB (20 mol%)
CTAB (20 mol%)
CTAB (20 mol%)
CTAB (20 mol%)
CTAB (20 mol%)
CTAB (20 mol%)
CTAB (20 mol%)
CTAB (20 mol%)
CTAB (20 mol%)
—
CTAB (20 mol%)
CTAB (20 mol%)
CTAB (20 mol%)
TBAI (20 mol%)
TBAB (20 mol%)
TBAC (20 mol%)
CTAB (10 mol%)
CTAB (5 mol%)
CTAB (1 mol%)
TBHP (4 eq.)
DCP (4 eq.)
TBPB (4 eq.)
BPO (4 eq.)
DDQ (4 eq.)
H2O2 (4 eq.)
DTBP (4 eq.)
DTBP (4 eq.)
DTBP (4 eq.)
DTBP (4 eq.)
DTBP (4 eq.)
DTBP (4 eq.)
DTBP (4 eq.)
—
DTBP (2 eq.)
DTBP (1 eq.)
DTBP (50 mol%)
DTBP (4 eq.)
DTBP (4 eq.)
DTBP (4 eq.)
DTBP (4 eq.)
DTBP (4 eq.)
DTBP (4 eq.)
DTBP (4 eq.)
DTBP (4 eq.)
DTBP (4 eq.)
DTBP (4 eq.)
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
EtOH
0
42
0
0
0
5
6
0
7a
8b
9c
83
62
61
0
85
0
88
0
0
0
0
0
0
10d
11e
12f
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
H2O
IPA
0
0
0
4
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
0
Trace
0
0
Reaction conditions: Diphenylphosphinic acid (0.1 mmol), toluene
(0.5 ml), 120 °C, 10 h. Yield was determined by 31P NMR spectroscopy;
CTAB (20 mol%); TBHP = tert-butylhydroperoxide 70% in water; H2O2
30% in water; DTBP = di-t-butylperoxide. a 140 °C. b 100 °C. c 80 °C.
d 60 °C. e 16 h. f In air.
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Table 2 CTAB-catalysed oxidative cross dehydrogenative coupling of
methylarenes with P(O)–OH compounds
Scheme 1 Control experiments.
Scheme 2 Proposed reaction mechanism.
Reaction conditions: Diphenylphosphinic acid (0.1 mmol), toluene
(0.5 ml), DTBP (0.4 mmol), CTAB (20 mol%), 120 °C, 10 h. Yield was
determined by 31P NMR spectroscopy.
that would couple with diphenylphosphinic acid to give the
corresponding product 3a.
activate the benzyl C–H bond for the generation of a benzylic
radical. This is the rate-determining step in the whole reaction.
Conclusions
The single electron of hydrogen could be captured by either 6 In this paper, we developed a practical metal-free method for
or 7 to regenerate CTAB. Nevertheless, the benzyl radical could the synthesis of organophosphorus compounds based on
be simultaneously oxidized by 6 or 7 to form a benzylic cation CTAB-catalysed oxidative cross dehydrogenative coupling of
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benzylic C(sp3)–H bonds in methylarenes with P(O)–OH com- CDCl3) δ 7.89–7.84 (m, 4H), 7.54–7.31 (m, 11H), 5.09 (d, J =
pounds. The protocol is simple and can circumvent the limit- 8.7 Hz, 2H). 13C NMR (100 MHz, CDCl3) δ 136.2 (d, J = 7.4 Hz),
ations of the previously reported methods. It tolerates a wide 132.1 (d, J = 2.7 Hz), 131.5 (d, J = 10.0 Hz), 131.2 (d, J =
range of functional groups, delivering organophosphorus com- 135.9 Hz), 128.4 (d, J = 8.2 Hz), 128.3 (s), 128.1 (s), 127.7 (s),
pounds in moderate to excellent yields. Moreover, different 66.1 (d, J = 5.5 Hz). 31P NMR (162 MHz, CDCl3) δ 32.17 (d, J =
types of C(sp3)–H bonds, no matter primary or secondary, can 19.1 Hz). MS-ESI: m/z 331.12, [M + Na]+.
couple with phosphinic acids or phosphoric diesters. The
4-Methyl-benzyl diphenylphosphinate (3b). Colorless oil,13,14
results of control and mechanistic experiments are generally Rf = 0.35 (petroleum ether/ethyl acetate = 2 : 1), melting point:
in agreement with the proposed pathway. This versatile proto- 87–88 °C 1H NMR (400 MHz, CDCl3) δ 7.76–7.71 (m, 4H),
col should provide a new avenue for the synthesis of phosphate 7.41–7.32 (m, 6H), 7.16–7.03 (m, 4H), 4.93 (d, J = 6.76 Hz, 2H),
esters with wide applications in the fields of biological, 2.23 (s, 3H). 13C NMR (100 MHz, CDCl3) δ 138.0 (s), 133.2 (d,
pharmaceutical, and materials chemistry.
J = 7.5 Hz), 132.0 (d, J = 2.8 Hz), 131.6 (d, J = 10.1 Hz), 131.3 (d,
J = 135.7 Hz), 129.1 (s), 128.5 (s), 128.3 (s), 127.9 (s), 66.2 (d, J =
5.6 Hz), 21.1 (s). 31P NMR (162 MHz, CDCl3) δ 32.1 (s). MS-ESI:
m/z 345.14, [M + Na]+.
Experimental
3-Methyl-benzyl diphenylphosphinate (3c). Yellow oil,14 Rf =
0.45 (petroleum ether/ethyl acetate = 2 : 1), 1H NMR (400 MHz,
CDCl3) δ 7.86–7.81 (m, 4H), 7.53–7.44 (m, 6H), 7.25–7.11 (m,
4H), 5.03 (d, J = 4.8 Hz, 2H), 2.33 (s, 3H). 13C NMR (100 MHz,
CDCl3) δ 138.1 (s), 136.1 (d, J = 7.4 Hz), 132.1 (d, J = 2.9 Hz),
131.7 (d, J = 10.1 Hz), 131.3 (d, J = 135.9 Hz), 129.0 (s), 128.7
(s), 128.6 (s), 128.5 (d, J = 13.0 Hz), 125.0 (s), 66.3 (d, J =
5.4 Hz), 21.3 (s). 31P NMR (162 MHz, CDCl3) δ 32.3 (s).
2-Methyl-benzyl diphenylphosphinate (3d). Colorless oil,13
Rf = 0.52 (petroleum ether/ethyl acetate = 2 : 1), 1H NMR
(400 MHz, CDCl3) δ 7.76–7.70 (m, 4H), 7.42–7.39 (m, 2H),
7.35–7.30 (m, 4H), 7.22 (d, J = 7.4 Hz, 1H), 7.13–7.05 (m, 3H),
4.99 (d, J = 6.2 Hz, 2H), 2.22 (s, 3H). 13C NMR (100 MHz,
CDCl3) δ 136.6 (s), 134.2 (d, J = 7.6 Hz), 132.1 (d, J = 2.9 Hz),
131.5 (d, J = 10.2 Hz), 131.7 (d, J = 135.6 Hz), 130.2 (s), 128.5
(d, J = 15.0 Hz), 128.5 (s), 128.4 (s), 125.9 (s), 64.6 (d, J =
5.5 Hz), 18.9 (s). 31P NMR (162 MHz, CDCl3) δ 32.3 (s).
HRMS-ESI: m/z 345.1023, ([M + Na]+, C20H19NaO2P+ calcd
345.1030).
General experimental procedures
The reactions were carried out in 25 mL Schlenk tubes under
N2. Unless otherwise noted, the materials from commercial
suppliers were used without further purification, whereas the
solvents were purified according to standard operating pro-
cedures. Flash column chromatography was performed using
Silica Gel 60 (300–400 mesh). Analytical thin layer chromato-
graphy (TLC) was performed on Haiyang TLC silica gel GF254
(0.25 mm) plates. The 1H NMR, 13C NMR and 31P NMR spectra
were recorded on a Bruker ADVANCE III spectrometer operat-
ing at 400 MHz, 100 MHz and 162 MHz respectively; and
chemical shifts were reported in ppm (δ) relative to internal
tetramethylsilane (TMS). Data were reported as follows:
chemical shift, multiplicity (s = singlet, d = doublet, t = triplet,
q = quartet, m = multiplet), and coupling constants (J) were
reported in hertz. The NMR yields were determined by
31P NMR with triphenylphosphine oxide (at 29.0 ppm) as the
internal standard. The reactions were monitored using GC-MS
QP 2010 equipment. The electron ionization (EI) approach was
used as the ionization method for HRMS measurement.
Fourier transform infrared spectroscopy (FT-IR, Thermo
Nicolet) was used to explore the chemical bonds of the
products.
3,5-Dimethylbenzyl diphenylphosphinate (3e). Yellow oil,13
Rf = 0.55 (petroleum ether/ethyl acetate = 2 : 1), 1H NMR
(400 MHz, CDCl3) δ 7.74–7.69 (m, 4H), 7.35–7.28 (m, 6H),
6.83–6.80 (m, 3H), 4.87 (d, J = 7.0 Hz, 2H), 2.14 (s, 6H). 13C
NMR (100 MHz, CDCl3) δ 137.8 (s), 135.8 (d, J = 7.3 Hz), 131.9
(d, J = 2.9 Hz), 131.4 (d, J = 10.1 Hz), 131.2 (d, J = 136.1 Hz),
130.0 (s), 128.2 (d, J = 13.1 Hz), 125.6 (s), 66.2 (d, J = 5.5 Hz),
21.0 (s). 31P NMR (162 MHz, CDCl3) δ 32.1 (s). HRMS-ESI:
General procedure for the synthesis of organophosphorus
compounds
To a 25 mL Schlenk tube, a mixture of P(O)–OH compound m/z 359.1180. ([M + Na]+, C21H21NaO2P+ calcd 359.1166).
(0.1 mmol), CTAB (20 mol%), DTBP (0.4 mmol) and methyl-
4-Fluoro-benzyl diphenylphosphinate (3f). Yellow oil,13,14
arenes (0.5 ml) was added with magnetic stirring at room Rf = 0.45 (petroleum ether/ethyl acetate = 2 : 1), 1H NMR
temperature. With constant stirring the mixture was heated to (400 MHz, CDCl3) δ 7.72–7.67 (m, 4H), 7.36–7.17 (m, 8H),
120 °C and kept at this temperature for 10 h. Then the reaction 6.88–6.84 (m, 2H), 4.90 (d, J = 7.1 Hz, 2H). 13C NMR (100 MHz,
solution was allowed to cool to ambient temperature, and then CDCl3) δ 162.3 (d, J = 245.4 Hz), 132.0 (d, J = 2.8 Hz), 131.9 (d,
transferred to a round-bottom flask. Silica gel (4.0 g) was J = 3.3 Hz), 131.3 (d, J = 10.1 Hz), 131.0 (d, J = 135.7 Hz), 129.6
added, and the solvent was removed under reduced pressure (d, J = 8.1 Hz), 128.3 (d, J = 13.1 Hz), 115.1 (d, J = 21.4 Hz), 65.3
to afford a free-flowing powder. This powder was then dry- (d, J = 5.5 Hz). 31P NMR (162 MHz, CDCl3) δ 32.4 (s).
loaded onto a silica gel column and purified by flash chrom- HRMS-ESI: m/z 349.0774, ([M + Na]+, C19H16FNaO2P+ calcd
atography using petroleum ether/ethyl acetate (5/1–2/1, v/v) as 349.0780).
the eluent to give the corresponding products.
4-Chlorobenzyl diphenylphosphinate (3g). Yellow oil,13,14
Benzyl diphenylphosphinate (3a). Colorless oil,13,14 Rf = 0.20 Rf = 0.55 (petroleum ether/ethyl acetate = 2 : 1), 1H NMR
(petroleum ether/ethyl acetate = 2 : 1), 1H NMR (400 MHz, (400 MHz, CDCl3) δ 7.72–7.67 (m, 4H), 7.35–7.29 (m, 6H),
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7.14 (s, 4H), 4.88 (d, J = 5.1 Hz). 13C NMR (100 MHz, CDCl3) 13C NMR (100 MHz, CDCl3) δ 133.5 (s), 132.1 (d, J = 2.7 Hz),
δ 134.6 (d, J = 7.2 Hz), 133.8 (s), 132.0 (d, J = 2.8 Hz), 131.3 (d, 131.7 (d, J = 7.4 Hz), 131.7 (d, J = 10.2 Hz), 131.1 (d, J =
J = 10.2 Hz), 130.8 (d, J = 135.7 Hz), 128.9 (s), 128.4 (s), 128.2 135.5 Hz), 129.2 (s), 128.5 (s), 128.4 (s), 128.3 (s), 126.7 (s),
(s), 65.2 (d, J = 5.4 Hz). 31P NMR (162 MHz, CDCl3) δ 32.6 (s). 126.4 (s), 125.8 (s), 125.0 (s), 123.4 (s), 64.6 (d, J = 5.4 Hz). 31P
HRMS-ESI: m/z 365.0473, ([M + Na]+, C19H16ClNaO2P+ calcd NMR (162 MHz, CDCl3) δ 32.5 (s).
365.0464).
(Naphthalen-2-yl)methyl diphenylphosphinate (3n). Yellow
3-Chlorobenzyl diphenylphosphinate (3h). Yellow oil,14 Rf = oil,13,14 Rf = 0.45 (petroleum ether/ethyl acetate = 2 : 1), 1H
0.48 (petroleum ether/ethyl acetate = 2 : 1), 1H NMR (400 MHz, NMR (400 MHz, CDCl3) δ 7.80–7.67 (m, 8H), 7.41–7.37 (m, 9H),
CDCl3) δ 7.85–7.80 (m, 4H), 7.55–7.46 (m, 6H), 7.34 (s, 1H), 5.13 (d, J = 6.9 Hz, 2H). 13C NMR (100 MHz, CDCl3) δ 133.7 (d,
7.28–7.24 (m, 3H), 5.03 (d, J = 7.0 Hz, 2H). 13C NMR (100 MHz, J = 7.4 Hz), 133.1 (d, J = 2.3 Hz), 132.2 (d, J = 2.8 Hz), 131.7 (s),
CDCl3) δ 138.4 (d, J = 7.3 Hz), 134.4 (s), 132.3 (d, J = 2.8 Hz), 131.6 (s), 131.3 (d, J = 135.7 Hz), 128.6 (s), 128.4 (s), 128.0 (s),
131.6 (d, J = 10.2 Hz), 130.3 (s), 130.0 (s), 129.1 (d, J = 127.6 (s), 127.0 (s), 126.2 (s), 126.2 (s), 125.6 (s), 66.5 (d, J =
144.8 Hz), 128.6 (d, J = 13.1 Hz), 127.8 (s), 125.8 (s), 65.3 (d, J = 5.5 Hz). 31P NMR (162 MHz, CDCl3) δ 32.5 (s). HRMS-ESI:
5.3 Hz). 31P NMR (162 MHz, CDCl3) δ 32.8 (s). HRMS-ESI: m/z 381.1024, ([M + Na]+, C23H19NaO2P+ calcd 381.1021).
m/z calcd for C19H16ClO2P: 342.0576 found 342.0575.
Quinolin-2-ylmethyl diphenylphosphinate (3o). Yellow oil,13
4-Bromobenzyl diphenylphosphinate (3i). Yellow oil,13,14 Rf = 0.22 (petroleum ether/ethyl acetate = 2 : 1), 1H NMR
Rf = 0.47 (petroleum ether/ethyl acetate = 2 : 1), 1H NMR (400 MHz, CDCl3) δ 8.14 (d, J = 8.5 Hz, 1H), 7.98 (d, J = 8.5 Hz,
(400 MHz, CDCl3) δ 7.85–7.80 (m, 4H), 7.51–7.44 (m, 8H), 7.23 1H), 7.85–7.75 (m, 4H), 7.76 (d, J = 8.3 Hz, 1H), 7.68–7.63 (m,
(d, J = 8.8 Hz, 2H), 5.00 (d, J = 8.76 Hz, 2H). 13C NMR 2H), 7.50–7.45 (m, 3H), 7.41–7.37 (m, 4H), 5.27 (d, J = 7.6 Hz,
(100 MHz, CDCl3) δ 135.2 (d, J = 7.1 Hz), 132.2 (d, J = 2.9 Hz), 2H). 13C NMR (100 MHz, CDCl3) δ 156.6 (d, J = 8.0 Hz), 147.1
131.5 (d, J = 1.7 Hz), 131.4 (s), 131.0 (d, J = 135.8 Hz), 129.4 (s), (s), 137.3 (s), 132.4 (d, J = 2.9 Hz), 131.7 (d, J = 10.2 Hz), 130.9
128.4 (d, J = 13.1 Hz), 122.1 (s), 65.4, (d, J = 5.4 Hz). 31P NMR (d, J = 136.3 Hz), 129.4 (d, J = 114.4 Hz), 128.7 (s), 128.6 (s),
(162 MHz, CDCl3) δ 32.7 (s). MS-ESI: m/z 409.14, [M + Na]+.
127.6 (s), 127.6 (s), 126.8 (s), 119.5 (s), 67.3 (d, J = 5.1 Hz). 31P
4-Iodobenzyl diphenylphosphinate (3j). Yellow oil,13,14 Rf = NMR (162 MHz, CDCl3) δ 33.4 (s). HRMS-ESI: m/z 382.0976,
0.45 (petroleum ether/ethyl acetate = 2 : 1), 1H NMR (400 MHz, ([M + Na]+, C22H18NNaO2P+ calcd 382.0972).
CDCl3) δ 7.74–7.69 (m, 4H), 7.55–7.50 (m, 2H), 7.39–7.31 (m,
4-Isopropylbenzyl diphenylphosphinate (3p). Yellow oil, Rf =
6H), 7.00–6.96 (m, 2H), 4.89 (d, J = 7.8 Hz, 2H). 13C NMR 0.55 (petroleum ether/ethyl acetate = 2 : 1), 1H NMR (400 MHz,
(100 MHz, CDCl3) δ 137.4 (s), 135.8 (d, J = 6.9 Hz), 132.2 (d, J = CDCl3) δ 7.77–7.72 (m, 4H), 7.44–7.40 (m, 2H), 7.36–7.35 (m,
2.9 Hz), 131.4 (d, J = 10.3 Hz), 130.9 (d, J = 135.8 Hz), 129.5 (s), 4H), 7.22–7.11 (m, 4H), 4.95 (d, J = 5.8 Hz, 2H), 2.87–2.76 (m,
128.4 (d, J = 13.2 Hz), 93.9 (s), 65.4 (d, J = 5.4 Hz). 31P NMR 1H), 1.15 (d, J = 5.2 Hz, 6H). 13C NMR (100 MHz, CDCl3)
(162 MHz, CDCl3)
δ 32.7 (d, J = 8.6 Hz). HRMS-ESI: δ 149.1 (s), 133.7 (d, J = 7.7 Hz), 132.1 (d, J = 2.9 Hz), 131.4 (d,
m/z 456.9833, ([M + Na]+, C19H16INaO2P+ calcd 456.9831).
J = 135.8 Hz), 131.7 (d, J = 10.1 Hz), 128.5 (d, J = 13.1 Hz), 128.1
[1,1′-Biphenyl]-4-ylmethyl diphenylphosphinate (3k). Yellow (s), 126.6 (s), 66.3 (d, J = 5.6 Hz), 33.9 (s), 23.9 (s). 31P NMR
oil,13 Rf = 0.35 (petroleum ether/ethyl acetate = 2 : 1), H NMR (162 MHz, CDCl3) δ 32.3 (s). HRMS-ESI: m/z 373.1412,
1
(400 MHz, CDCl3) δ 7.75–7.70 (m, 4H), 7.43–7.41 (m, 4H), ([M + Na]+, C22H23NaO2P+ calcd 373.1402). IR (neat): ν = 2917,
7.34–7.25 (m, 10H), 7.19–7.15 (m, 1H), 4.97 (d, J = 6.7 Hz, 2H). 1601, 1374, 1280, 1223, 1011 cm−1
.
13C NMR (100 MHz, CDCl3) δ 141.0 (s), 140.3 (s), 135.1 (d, J =
4-(tert-Butyl)benzyl diphenylphosphinate (3q). Yellow oil,14
7.2 Hz), 132.0 (d, J = 2.7 Hz), 131.4 (d, J = 10.1 Hz), 131.1 (d, J = Rf = 0.60 (petroleum ether/ethyl acetate = 2 : 1), 1H NMR
135.8 Hz), 128.6 (s), 128.4 (s), 128.2 (d, J = 9.7 Hz), 127.2 (s), (400 MHz, CDCl3) δ 7.76–7.72 (m, 4H), 7.42–7.38 (m, 2H),
127.0 (s), 126.8 (s), 65.9 (d, J = 5.5 Hz). 31P NMR (162 MHz, 7.34–7.31 (m, 4H), 7.28–7.20 (m, 4H), 4.95 (d, J = 6.7 Hz, 2H),
CDCl3) δ 32.4 (s). MS-ESI: m/z 407.14, [M + Na]+.
1.21 (s, 9H). 13C NMR (100 MHz, CDCl3) δ 151.2 (s), 133.2 (d,
2-Methoxybenzyl diphenylphosphinate (3l). Yellow oil, Rf = J = 7.5 Hz), 132.1 (d, J = 2.9 Hz), 131.6 (d, J = 10.2 Hz), 131.3 (d,
0.43 (petroleum ether/ethyl acetate = 2 : 1), 1H NMR (400 MHz, J = 135.8 Hz), 128.4 (d, J = 13.1 Hz), 127.7 (s), 125.4 (s), 66.1 (d,
CDCl3) δ 7.78–7.73 (m, 4H), 7.42–7.33 (m, 7H), 7.21–7.17 (m, J = 5.5 Hz), 34.5 (s), 31.2 (s). 31P NMR (162 MHz, CDCl3) δ
1H), 6.87–6.84 (m, 1H), 6.73 (d, J = 8.2 Hz, 1H), 5.05 (d, J = 32.1 (s).
6.3 Hz, 2H), 3.64 (s, 3H). 13C NMR (100 MHz, CDCl3) δ 157.0
1-Phenylethyl diphenylphosphinate (3r). Yellow oil,13 Rf =
(s), 132.0 (d, J = 2.9 Hz), 131.5 (d, J = 136.2 Hz), 131.6 (d, J = 0.63 (petroleum ether/ethyl acetate = 2 : 1), 1H NMR (400 MHz,
10.2 Hz), 129.4 (s), 129.0 (s), 128.4 (s), 128.3 (s), 124.7 (d, J = CDCl3) δ 7.88–7.83 (m, 2H), 7.69–7.64 (m, 2H), 7.49–7.40 (m,
7.9 Hz), 120.3 (s), 110.1 (s), 61.8 (d, J = 5.2 Hz), 55.1 (s). 4H), 7.30 (s, 7H), 5.56–5.49 (m, 1H), 1.66 (d, J = 6.6 Hz, 3H).
31P NMR (162 MHz, CDCl3)
δ
32.1 (s). HRMS-ESI: 13C NMR (100 MHz, CDCl3) δ 141.9 (d, J = 5.1 Hz), 132.5 (d, J =
m/z 361.0992, ([M + Na]+, C20H19NaO3P+ calcd 361.0990). 93.5 Hz), 131.9 (d, J = 2.8 Hz), 131.8 (d, J = 2.8 Hz), 131.7 (d, J =
IR (neat): ν = 2928, 2824, 1593, 1248, 1290, 1257, 1034 cm−1
10.2 Hz), 131.3 (d, J = 10.0 Hz), 131.1 (d, J = 88.4 Hz), 128.4 (s),
.
(Naphthalen-1-yl)methyl diphenylphosphinate (3m). Yellow 128.3 (s), 128.2 (s), 128.2 (s), 128.1 (s), 74.4 (d, J = 5.6 Hz), 24.9
1
oil,14 Rf = 0.39 (petroleum ether/ethyl acetate = 2 : 1), H NMR (d, J = 3.2 Hz). 31P NMR (162 MHz, CDCl3) δ 31.1 (s).
(400 MHz, CDCl3) δ 7.97 (d, J = 8.1 Hz, 1H), 7.71–7.66 (m, 6H), HRMS-ESI: m/z 345.1021, ([M + Na]+, C20H19NaO2P+ calcd
7.41–7.31 (m, 5H), 7.27–7.23 (m, 5H), 5.41 (d, J = 6.6 Hz, 2H). 345.1021).
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Benzhydryl diphenylphosphinate (3s). Yellow oil,16 Rf = 0.65 C15H24ClNaO4P+ calcd 357.0990). IR (neat): ν = 2928, 1609,
(petroleum ether/ethyl acetate
=
2 : 1), melting point: 1269, 1053, 796 cm−1
.
302–303 °C 1H NMR (400 MHz, CDCl3) δ 7.66–7.61 (m, 4H),
Dibutyl(4-iodobenzyl)phosphate (4e). Yellow oil, Rf = 0.35
7.37–7.34 (m, 2H), 7.25–7.14 (m, 14H), 6.40 (d, J = 10.1 Hz, (petroleum ether/ethyl acetate = 2 : 1), 1H NMR (400 MHz,
1H). 13C NMR (100 MHz, CDCl3) δ 140.6 (d, J = 4.1 Hz), 131.9 CDCl3) δ 7.62 (d, J = 8.0 Hz, 2H), 7.06 (d, J = 7.9 Hz, 2H), 4.92
(d, J = 2.5 Hz), 131.7 (d, J = 10.2 Hz), 131.5 (d, J = 136.2 Hz), (d, J = 8.5 Hz, 2H), 3.97–3.91 (m, 4H), 1.59–1.53 (m, 4H),
128.3 (s), 128.1 (s), 127.8 (s), 127.1 (s), 78.5 (d, J = 5.5 Hz). 31P 1.35–1.27 (m, 4H), 0.86–0.82 (m, 6H). 13C NMR (100 MHz,
NMR (162 MHz, CDCl3) δ 32.3 (s). HRMS-ESI: m/z 407.1194, CDCl3) δ 137.5 (s), 135.7 (d, J = 6.6 Hz), 129.5 (s), 94.0 (s), 68.1
([M + Na]+, C25H21NaO2P+ calcd 407.1190).
(d, J = 5.4 Hz), 67.5 (d, J = 6.0 Hz), 32.1 (d, J = 7.0 Hz), 18.5 (s),
1,2-Diphenylethyl diphenylphosphinate (3t). Yellow oil,17 13.5 (s). 31P NMR (162 MHz, CDCl3) δ −0.74 (s). HRMS-ESI:
Rf = 0.60 (petroleum ether/ethyl acetate = 2 : 1), melting point: m/z 449.0382, ([M + Na]+, C15H24INaO4P+ calcd 449.0380).
141–142 °C 1H NMR (400 MHz, CDCl3) δ 7.70–7.61 (m, 4H), IR (neat): ν = 2928, 1560, 1271, 1034, 539 cm−1
7.53–7.49 (m, 1H), 7.42–7.38 (m, 3H), 7.32–7.28 (m, 2H),
.
Dibutyl(naphthalen-2-ylmethyl)phosphate (4f). Yellow oil,19
7.24–7.19 (m, 8H), 7.03 (s, 2H), 5.55 (q, J = 7.5 Hz, 1H), 3.42 Rf = 0.35 (petroleum ether/ethyl acetate = 2 : 1), 1H NMR
(dd, J = 13.6, 6.4 Hz, 1H), 3.24 (dd, J = 13.6, 7.1 Hz, 1H). 13C (400 MHz, CDCl3) δ 7.77–7.73 (m, 4H), 7.43–7.38 (m, 3H), 5.14
NMR (100 MHz, CDCl3) δ 139.9 (d, J = 3.6 Hz), 136.4 (s), 132.3 (d, J = 8.3 Hz, 2H), 3.96–3.91 (m, 4H), 1.56–1.49 (m, 4H),
(d, J = 47.0 Hz), 131.9 (d, J = 2.9 Hz), 131.8 (s), 131.8 (d, J = 1.32–1.22 (m, 4H), 0.81–0.77 (m, 6H). 13C NMR (100 MHz,
0.2 Hz), 131.7 (s), 131.4 (d, J = 10.2 Hz), 131.0 (d, J = 43.7 Hz), CDCl3) δ 133.4 (d, J = 6.6 Hz), 133.1 (s), 133.0 (s), 128.3 (s),
129.9 (s), 128.4 (s), 128.2 (d, J = 6.3 Hz), 128.0 (s), 127.9 (s), 127.9 (s), 127.6 (s), 126.8 (s), 126.3 (s), 126.2 (s), 125.3 (s), 69.1
126.6 (s), 126.5 (s), 78.9 (d, J = 5.9 Hz), 45.2 (d, J = 4.6 Hz). 31P (d, J = 5.5 Hz), 67.5 (d, J = 6.1 Hz), 32.1 (d, J = 6.9 Hz), 18.5 (s),
NMR (162 MHz, CDCl3) δ 31.5 (s). HRMS-ESI: m/z 421.1289, 13.4 (s). 31P NMR (162 MHz, CDCl3) δ −0.60 (s).
([M + Na]+, C26H23NaO2P+ calcd 421.1287).
Benzyl diethyl phosphate (4g). Yellow oil,13 Rf = 0.50 (pet-
1
Benzyl dibutyl phosphate (4a). Yellow,13 Rf = 0.75 (petroleum roleum ether/ethyl acetate = 2 : 1), H NMR (400 MHz, CDCl3)
ether/ethyl acetate
=
2 : 1), 1H NMR (400 MHz, CDCl3) δ 7.40–7.35 (m, 5H), 5.07 (d, J = 8.2 Hz, 2H), 4.10–4.05 (m, 4H),
δ 7.30–7.26 (m, 5H), 4.98 (d, J = 8.4 Hz, 2H), 3.93 (d, J = 7.2 Hz, 1.32–1.29 (m, 6H). 13C NMR (100 MHz, CDCl3) δ 136.1 (s),
4H), 1.58–1.52 (m, 4H), 1.34–1.27 (m, 4H), 0.85–0.81 (m, 6H). 128.5 (s), 128.4 (s), 127.8 (s), 69.0 (d, J = 5.5 Hz), 63.8 (d, J =
13C NMR (100 MHz, CDCl3) δ 136.0 (d, J = 6.7 Hz), 128.3 (s), 5.9 Hz), 16.0 (d, J = 6.6 Hz). 31P NMR (162 MHz, CDCl3)
128.2 (s), 127.6 (s), 68.8 (d, J = 5.4 Hz), 67.3 (d, J = 6.2 Hz), 32.0 δ −0.92 (s).
(d, J = 6.9 Hz), 18.4 (s), 13.4 (s). 31P NMR (162 MHz, CDCl3)
δ −0.7 (s). MS-ESI: m/z 323.12, [M + Na]+.
Diethyl(4-iodobenzyl)phosphate (4h). Yellow oil, Rf = 0.29
(petroleum ether/ethyl acetate = 2 : 1), 1H NMR (400 MHz,
CDCl3) δ 7.71 (d, J = 8.4 Hz, 2H), 7.30–7.13 (m, 2H), 5.00 (d, J =
Dibutyl(3-methylbenzyl)phosphate (4b). Yellow oil,18 Rf
=
0.77 (petroleum ether/ethyl acetate = 2 : 1), 1H NMR (400 MHz, 10.0 Hz, 2H), 4.13–4.06 (m, 4H), 1.33–1.29 (m, 6H). 13C NMR
CDCl3) δ 7.25–7.15 (m, 4H), 5.03 (d, J = 8.3 Hz, 2H), 4.05–4.00 (100 MHz, CDCl3) δ 137.7 (s), 135.7 (d, J = 6.9 Hz), 129.6 (s),
(m, 4H), 2.35 (s, 3H), 1.65–1.61 (m, 4H), 1.43–1.35 (m, 4H), 94.1 (s), 68.2 (d, J = 5.4 Hz), 63.9 (d, J = 5.8 Hz), 16.1 (d, J =
0.94–0.89 (m, 6H). 13C NMR (100 MHz, CDCl3) δ 138.1 (s), 6.6 Hz). 31P NMR (162 MHz, CDCl3) δ −0.93 (s). HRMS-ESI: m/z
135.9 (d, J = 6.6 Hz), 129.0 (s), 128.4 (s), 128.3 (s), 124.8 (s), 392.9821, ([M + Na]+, C11H16INaO4P+ calcd 392.9814).
68.9 (d, J = 5.6 Hz), 67.3 (d, J = 5.9 Hz), 32.1 (d, J = 6.9 Hz), 21.2
Diethyl(naphthalen-2-ylmethyl)phosphate (4i). Yellow oil,13
Rf = 0.50 (petroleum ether/ethyl acetate = 2 : 1), 1H NMR
(400 MHz, CDCl3) δ 7.84 (d, J = 3.2 Hz, 4H), 7.49 (s, 3H), 5.23
(s), 18.5 (s), 13.4 (s). 31P NMR (162 MHz, CDCl3) δ −0.7 (s).
Dibutyl(2-methylbenzyl)phosphate (4c). Yellow oil,18 Rf
=
0.49 (petroleum ether/ethyl acetate = 2 : 1), 1H NMR (400 MHz, (d, J = 8.2 Hz, 2H), 4.12–4.08 (m, 4H), 1.32–1.28 (m, 6H). 13C
CDCl3) δ 7.37–7.17 (m, 4H), 5.08 (d, J = 7.6 Hz, 2H), 4.04–3.99 NMR (100 MHz, CDCl3) δ 133.4 (d, J = 6.8 Hz), 133.1 (d, J =
(m, 4H), 2.37–2.33 (m, 3H), 1.64–1.58 (m, 4H), 1.42–1.35 (m, 8.3 Hz), 128.4 (s), 128.0 (s), 127.6 (s), 126.9 (s), 126.3 (s),
4H), 0.93–0.89 (m, 6H). 13C NMR (100 MHz, CDCl3) δ 136.5 (s), 126.3 (s), 125.4 (s), 69.1 (d, J = 5.4 Hz), 63.8 (d, J = 5.8 Hz), 16.0
133.9 (d, J = 7.0 Hz), 130.1 (s), 128.6 (s), 128.5 (s), 125.8 (s), (d, J = 6.8 Hz). 31P NMR (162 MHz, CDCl3) δ −0.84 (s).
67.2 (d, J = 6.1 Hz), 67.1 (d, J = 6.0 Hz), 32.0 (d, J = 6.7 Hz), 18.5
(d, J = 3.1 Hz), 18.4 (s), 13.3 (s). 31P NMR (162 MHz, CDCl3)
δ −0.69 (s).
Conflicts of interest
Dibutyl(4-chlorobenzyl)phosphate (4d). Yellow oil, Rf = 0.40
(petroleum ether/ethyl acetate = 2 : 1), 1H NMR (400 MHz, There are no conflicts to declare.
CDCl3) δ 7.36–7.31 (m, 4H), 5.03 (d, J = 8.6 Hz, 2H), 4.04–3.99
(m, 4H), 1.66–1.59 (m, 4H), 1.42–1.33 (m, 4H), 0.93–0.89 (m,
6H). 13C NMR (100 MHz, CDCl3) δ 134.6 (d, J = 6.6 Hz),
Acknowledgements
134.3 (s), 129.1 (s), 128.7 (s), 68.1 (d, J = 5.4 Hz), 67.6 (d, J =
6.1 Hz), 32.2 (d, J = 6.9 Hz), 18.6 (s), 13.5 (s). 31P NMR This work was financially supported by the National Natural
(162 MHz, CDCl3) δ −0.7 (s). 31P NMR (162 MHz, CDCl3) Science Foundation of China (Grant No. 21476065, 21571060,
δ
32.3 (s). HRMS-ESI: m/z 357.0997, ([M
+
Na]+, 21725602) and the Fundamental Research Funds for the
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Central Universities (Hunan University). C.-T. Au thanks
Hunan University for an adjunct professorship.
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