Solvent-free synthesis of Tertiaryα-Hydroxyphosphates by the Triethylamine-catalyzed hydrophosphonylation of ketones

Article abstract of DOI:10.1080/10426507.2013.765874

A new, environmentally benign, convenient, and easy method of synthesizing tertiary α-hydroxyphosphonates by the triethylamine-catalyzed hydrophosphonylation of unactivated ketones was developed. In the presence of triethylamine, aromatic or heteroaromati

Full text of DOI:10.1080/10426507.2013.765874

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Solvent-Free Synthesis of
Tertiaryα-Hydroxyphosphates
by the Triethylamine-Catalyzed
Hydrophosphonylation of Ketones
Chubei Wang a , Jianwei Zhou a , Xingbin Lv a , Junlei Wen a &
Hongwu He b
a Institute of Energy and Fuel , Xinxiang University , Xinxiang ,
Henan , P. R. China
b Key Laboratory of Pesticide and Chemical Biology, Ministry of
Education, College of Chemistry , Central China Normal University ,
Wuhan , Hubei , P. R. China
Accepted author version posted online: 25 Feb 2013.Published
online: 06 Sep 2013.
To cite this article: Chubei Wang , Jianwei Zhou , Xingbin Lv , Junlei Wen & Hongwu He
(2013) Solvent-Free Synthesis of Tertiaryα-Hydroxyphosphates by the Triethylamine-Catalyzed
Hydrophosphonylation of Ketones, Phosphorus, Sulfur, and Silicon and the Related Elements, 188:10,
1334-1339, DOI: 10.1080/10426507.2013.765874
To link to this article: http://dx.doi.org/10.1080/10426507.2013.765874
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Phosphorus, Sulfur, and Silicon, 188:1334–1339, 2013
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2013.765874
SOLVENT-FREE SYNTHESIS
OF TERTIARYα-HYDROXYPHOSPHATES
BY THE TRIETHYLAMINE-CATALYZED
HYDROPHOSPHONYLATION OF KETONES
Chubei Wang,1 Jianwei Zhou,1 Xingbin Lv,1 Junlei Wen,1
and Hongwu He2
1Institute of Energy and Fuel, Xinxiang University, Xinxiang, Henan, P. R. China
2Key Laboratory of Pesticide and Chemical Biology, Ministry of Education, College
of Chemistry, Central China Normal University, Wuhan, Hubei, P. R. China
GRAPHICAL ABSTRACT
Abstract A new, environmentally benign, convenient, and easy method of synthesizing tertiary
α-hydroxyphosphonates by the triethylamine-catalyzed hydrophosphonylation of unactivated
ketones was developed. In the presence of triethylamine, aromatic or heteroaromatic ketones
can react with phosphite to form tertiary α-hydroxyphosphonates under solvent-free and mild
conditions. The proposed method was also suitable for functionalized ketones.
Supplementary materials are available for this article. Go to the publisher’s online edition of
Phosphorus, Sulfur, and Silicon and the Related Elements for the following free supplemental
files: Additional text and figures.
Keywords Phosphite; hydrophosphonylation; ketone; solvent-free
INTRODUCTION
Hydroxyphosphonates are important compounds because of their remarkable activi-
ties.1,2 These compounds are widely used as enzyme inhibitors,3 antiviral agents,4–8 antis-
chistosomal agents,9 and anti-HIV agents.10 In addition, α-hydroxyphosphonates are attrac-
tive precursors in the synthesis of α-substituted phosphonates and phosphonic acids.11,12
Received 24 November 2012; accepted 9 January 2013.
This work was supported by the Education Department of Henan Province (no. 12B210022), the Science
and Technology Department of Henan Province (no. 2010HASTIT040), and Xinxiang University (12ZB10).
Address correspondence to Chubei Wang, Institute of Energy and Fuel, Xinxiang University, Jinsui Road,
Xinxiang, Henan 453003, P. R. China. E-mail: wangchubei@163.com
1334

SYNTHESIS OF TERTIARYα-HYDROXYPHOSPHATES
1335
Thus, the synthesis of α-hydroxyphosphonates and their functionalized derivatives is a
significant objective.13,14
A series of α-substituted phosphonates has been synthesized and examined for
their biological activities by our group.15 Although numerous methods of preparing
α-hydroxyphosphonates are available,16–18 the synthesis of tertiary α-hydroxyphosphonates
still attracts considerable attention. The traditional synthesis of tertiary α-hydroxyphos-
phonates involves a reaction between phosphite and unactivated ketones in the presence
of various bases. However, strong basic catalysts potentially exclude the hydrophospho-
nylation of base-sensitive ketones. Zhou et al.19 used (i-PrO)4Ti as catalyst in the hy-
drophosphonylation of ketones with a broad substrate scope. Wang et al.20,21 and Sarazin
et al.22 used metal amido complexes as catalysts for the hydrophosphonylation of unacti-
vated ketones. Seven et al.23 prepared tertiary hydroxyphosphonates from organoaluminum
reagents and acyl phosphonates. A direct hydrophosphonylation of ketones also proceeds
when pyridine 2,6-dicarboxylic acid is used as a bifunctional organocatalyst.24 However,
all existing methods have disadvantages such as environmental pollution caused by organic
solvents, extreme reaction conditions, unsatisfactory yields, and complicated operations.
Therefore, an efficient and convenient method of constructing this significant scaffold must
be developed.
Solvent-free organic synthesis has advantages over its homogeneous counterparts be-
cause of the rising concern on the effects of organic solvents on the environment and human
health, in addition to economic demands and simple processes.25 In this article, we describe
the solvent-free synthesis of tertiary α-hydroxyphosphonates by the hydrophosphonylation
of unactivated ketones (see Scheme 1).
Scheme 1
RESULTS AND DISCUSSION
A preliminary survey revealed that mildly basic triethylamine was a promising cata-
lyst for the hydrophosphonylation of acetophenone (see Table 1, entries 1–8). With 50 mol%
triethylamine, the corresponding product was obtained with 35% isolated yield for 4 h
without any byproduct. Pyridine was a better catalyst in terms of reactivity. Compared with
triethylamine, separating pyridine from the reaction mixture was difficult. If the product
contained an extremely small amount of pyridine, a foul smell was emitted. The product
was washed with water several times. By contrast, the other tertiary amines gave 3a with
≤30% yield. The commercially available triethylamine was used as the catalyst. Separating
triethylamine from reaction mixtures was easy. Triethylamine was purified using a rotatory
evaporator and recycled.
An intensive investigation of the reaction conditions revealed that the triethy-
lamine concentration played a crucial role in the reaction. The results are summarized in
Table 1 (entries 9–12). By increasing the triethylamine concentration, the yield improved.

1336
C. WANG ET AL.
Table 1 Optimization of the reaction conditions
Entry
Catalyst (mol%)
Time (h)
Yielda (%)
1
2
3
4
5
6
7
8
9
N,N-Dimethylaniline (50)
Tri-n-butylamine (50)
Triisobutyamine (50)
Tri-n-propylamine (50)
Triisopropylamine (50)
Dimethylheptylamine (50)
Pyridine (50)
Triethylamine (50)
Triethylamine (80)
Triethylamine (100)
Triethylamine (120)
Triethylamine (150)
4
4
4
4
4
4
4
4
2
2
2
2
20
15
9
16
7
21
29
35
81
93
93
93
10
11
12
aThe products were purified by silica gel column chromatography (petroleum ether–ethyl acetate, 2:1, v:v).
The optimal result was obtained when the model reaction was allowed to proceed at
room temperature under solvent-free conditions. The reaction smoothly proceeded with
100 mol% catalyst for 2 h (see Table 1, entry 10). Increased amount of catalyst did not
improve the yield. Compared with other catalysts, triethylamine had some advantages such
as mild reaction conditions, few side reactions, moisture stability, low toxicity, and simple
operation.
A series of ketones with different substituents on the aromatic ring was subjected to
the addition reaction from ambient temperature to 40 ◦C for 2 h. Regardless of the electronic
nature and location of substituents on the aromatic ring, the reaction of aromatic ketones
showed high reactivities. The current system was extended to the hydrophosphonylation of
heteroaromatic and aliphatic ketones, giving the corresponding products in good yields (see
Table 2, entries 13–15). The mild alkalinity of triethylamine made it an effective catalyst
for the reaction of chloroacetone, which contains a base-sensitive functional group (see
Table 2, entry 16). Benzophenone exhibited reduced reactivities because of its intrinsic
lower reactivity, but it was also an effective substrate for this reaction system (see Table 2,
entry 17).
The corresponding products were isolated in good yields (63%–89%; see Table 2),
and the structures of products 3a–3q were characterized by 1H NMR, 13C NMR, 31P NMR,
IR, MS (mass spectrum), and elemental analysis (see Supplemental Materials).
The products exhibited some characteristic peaks at δ = 1.24–2.08 ppm (d or m, 3H
or 2H, P−C−CH3 or P−C−CH2) and at δ = 5.3–6.7 ppm (s or d, 1H, P−C−OH),
1
respectively, in H NMR. The typical carbon resonance was at about δ ≈ 53 ppm
and δ = 69–78 ppm (d or dd) in the 13C NMR spectra of the products, respectively,
which also confirmed the presence of a P−OMe group and a P−C bond. The typ-
ical phosphorus resonance was at δ = 20–33 ppm in the 31P NMR spectra of the
products.

SYNTHESIS OF TERTIARYα-HYDROXYPHOSPHATES
Table 2 Physical constants of compound 3
1337
No.
R1
R2
Appearance
Melting point (◦C)
Yielda (%)
3a
3b
3c
3d
3e
3f
3g
3h
3i
3j
3k
3l
3m
3n
3o
3p
3q
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
n-Pr
Me
Me
Me
Me
Ph
Ph
White solid
White solid
White solid
White solid
White solid
White solid
White solid
White solid
White solid
White solid
White solid
White solid
Off-white solid
Off-white solid
White solid
White solid
White solid
136.9–137.7 (lit.23142–143)
147.3–148.8 (lit.23143–144)
142.0–143.6 (lit.23136–137)
149.5–151.1 (lit.23161–162)
112.6—113.9
82
81
84
86
85
84
86
87
85
84
76
78
74
75
88
89
63b
2-ClPh
3-ClPh
4-ClPh
3-BrPh
4-BrPh
2-FPh
154.2–155.8 (lit.26160)
126.1–126.8
4-FPh
129.1–130.6 (lit.23157–158)
144.2–145.5
138.2–139.7 (lit.23156–157)
161.6–162.7 (lit.23172–173)
113.2–114.6 (lit.27127.5–128)
74.4–75.7
2, 4-Cl2Ph
4-MePh
4-MeOPh
Ph
2-Furyl
2-Thienyl
Me
78.6–80.1
68.6–70.2 (lit.2872)
ClCH2
Ph
72.5–73.8 (lit.2973–74)
149.1–150.6 (lit.28,30171)
aIsolated yield.
bReaction time was 12 h.
CONCLUSION
In summary, an easy, solvent-free approach to the synthesis of tertiary α-
hydroxyphosphonates using triethylamine as a catalyst was developed. The mild base
catalyst was applied to the hydrophosphonylation of different ketones including ben-
zophenone, giving the corresponding quaternary α-hydroxyphosphonates in satisfactory
yields. The proposed method was suitable for functionalized ketones and can be a valuable
addition to the existing methods of preparing tertiary α-hydroxyphosphonates.
EXPERIMENTAL
Column chromatography was carried out with Merck silica gel (230–400 mesh). Thin-
layer chromatography was performed on silica gel GF-254. Melting points were measured
on a WRS-1B electrothermal melting point apparatus and uncorrected. IR spectra were
recorded in potassium bromide disks using an AVATAR360 FTIR spectrophotometer. Only
1
the most significant absorption bands were recorded. H NMR and 13C NMR spectra
were recorded on a 600 MHz spectrophotometer. 31P NMR spectra were recorded on a
400 MHz spectrophotometer using phosphoric acid (85 wt% H3PO4) as an internal standard.
Chemical shifts (δ) are given in parts per million, and coupling constants (J) are given in
hertz. Multiplicities are indicated by s (singlet), d (doublet), t (triplet), q (quartet), and m
(multiplet). MS was performed on a Finnigan TRACE spectrometer and API2000LC/MS.
Elemental analyses (C, H, and N) were analyzed on a Vario EL III CHNSO elemental
analyzer. The results were within 0.5% of the theoretical values.

1338
C. WANG ET AL.
General Procedure for the Synthesis of Compounds 3a–3q
A mixture of substituted ketones 1 (11 mmol), phosphite 2 (◦10 mmol), and triethy-
lamine (10 mmol) were stirred from ambient temperature to 40 C for 2 h. The crude
product was collected by filtration and recrystallized from ethyl acetate to afford pure
α-hydroxyphosphonates 3.
Selected Spectroscopic Data of New Compounds
Dimethyl (1-(3-bromophenyl)-1-hydroxyethyl)phosphonate (3e): 1H NMR
(600 MHz, DMSO-d6, ppm): δ 7.70 (s, 1H, Ar–H), 7.51 (d, 1H, J = 7.8 Hz, Ar–H), 7.47
(d, 1H, J = 7.8 Hz, Ar–H), 7.31 (d, 1H, J = 7.8 Hz, Ar–H), 6.22 (d, 1H, J = 10.8 Hz,
P–OH), 3.54–3.66 (m, 6H, 2×O–CH3), 1.66 (d, 3H, J = 15.6 Hz, P–C–CH3); 13C NMR
(150 MHz, DMSO-d6, ppm): δ 145.5, 129.8, 128.8, 128.7, 125.2, 121.2, 73.2, 72.6 (d,
J = 172.8 Hz), 53.6, 25.4; 31P NMR (160 MHz, DMSO-d6, ppm): δ 26.3; MS (m/z,%):
308 (M+ 6.21), 310 (6.12), 199 (10.21), 183 (100), 126 (51.37), 109 (53.21); IR (KBr):
3436, 2956, 1458, 1231, 1068, 783 cm−1; Calcd. for C10H14BrO4P: C 38.86, H 4.57;
Found: C 38.64, H 4.67.
Dimethyl (1-(2,4-dichlorophenyl)-1-hydroxyethyl)phosphonate (3i): 1H NMR
(600 MHz, DMSO-d6, ppm): δ 7.85 (d, 1H, J = 9.0 Hz, Ar–H), 7.51 (d, 1H, J = 13.2 Hz,
Ar–H), 7.44 (d, 1H, J = 8.4 Hz, Ar–H), 6.32 (d, 1H, J = 12 Hz, P–OH), 3.60–3.67 (m, 6H,
2×O–CH3), 1.90 (d, 3H, J = 15 Hz, P–C–CH3); 13C NMR (150 MHz, DMSO-d6, ppm):
δ 138.7, 132.6, 132.2, 131.6, 130.4, 126.6, 73.8 (d, J = 176.3 Hz), 53.5, 24.5; 31P NMR
(160 MHz, DMSO-d6, ppm): δ 24.9; MS (m/z,%): 298 (M+ 7.31), 300 (4.42), 190 (15.26),
175 (63.84), 173 (100), 126 (56.41), 109 (41.78); IR (KBr): 3445, 2954, 1465, 1223, 1070,
861, 798 cm-1; Calcd. for C10H13Cl2O4P: C 40.16, H 4.38; Found: C 40.28, H 4.52.
Dimethyl (1-hydroxy-1-phenylbutyl)phosphonate (3l): 1H NMR (600 MHz,
DMSO-d6, ppm): δ 7.50 (d, 2H, J = 7.8 Hz, Ar–H), 7.33 (m, 2H, Ar–H), 7.24 (m, 1H,
Ar–H), 5.81 (d, 1H, J = 5.4 Hz, P–OH), 3.43–3.65 (m, 6H, 2×O–CH3), 2.07 (m, 1H,
PhCCH2CH2CH3), 1.99 (m, 1H, PhCCH2CH2CH3), 1.30 (m, 1H, PhCCH2CH2CH3), 0.78
(m, 4H, PhCCH2CH2CH3, PhCCH2CH2CH3); 13C NMR (150 MHz, DMSO-d6, ppm): δ
140.1, 127.6, 126.6, 126.2, 76.3, 75.8 (d, J = 168.8 Hz), 53.4 (d, J = 8.0 Hz), 53.3 (d, J =
8.2 Hz), 14.9, 14.8, 14.0; 31P NMR (160 MHz, DMSO-d6, ppm): δ 26.2; MS (m/z,%): 258
(M+ 25.71), 149 (10.52), 133 (100), 126 (37.41), 109 (46.83); IR (KBr): 3411, 2961, 1450,
1227, 1066, 776 cm−1; Calcd. for C12H19O4P: C 55.81, H 7.42; Found: C 55.73, H 7.61.
Dimethyl (1-(furan-2-yl)-1-hydroxyethyl)phosphonate (3m): 1H NMR (600 MHz,
DMSO-d6, ppm): δ 7.63 (s, 1H, 5-Furyl–H), 6.43 (m, 1H, 4-Furyl–H), 6.41 (m, 1H, 3-
Furyl–H), 6.11 (d, 1H, J = 12 Hz, P–OH), 3.60–3.65 (m, 6H, 2×O–CH3), 1.61 (d, 3H,
J = 15.0 Hz, P–C–CH3); 13C NMR (150 MHz, DMSO-d6, ppm): δ 154.5, 142.4 (d, J =
15.0 Hz), 110.4, 107.3, 69.1 (d, J = 179.5 Hz), 53.3, 22.7; 31P NMR (160 MHz, DMSO-d6,
ppm): δ 24.7; MS (m/z,%): 220 (M+ 17.68), 111 (9.36), 109 (37.54), 93 (100); IR (KBr):
3414, 2958, 1456, 1225, 1157, 1049, 841 cm−1; Calcd. for C8H13O5P: C 43.64, H 5.95;
Found: C 43.53, H 6.11.
SUPPLEMENTAL MATERIALS
Data for products 3a–3q are available. Supplemental Materials associated with this
article can be found in the online version.

SYNTHESIS OF TERTIARYα-HYDROXYPHOSPHATES
1339
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