Cyanide ion promoted addition of acylphosphonates to diethyl cyanophosphonate: Synthesis of phosphonocyanohydrin O-phosphates

Article abstract of DOI:10.1055/s-0029-1216634

Cyanide ion catalyzed addition of acylphosphonates to diethyl cyanophosphonate furnished phosphonocyanohydrin O-phosphates in high yield. The reaction works via the phosphonate-phosphate rearrangement, followed by the addition of diethyl cyanophosphonate

Full text of DOI:10.1055/s-0029-1216634

PAPER
1655
Cyanide Ion Promoted Addition of Acylphosphonates to Diethyl
Cyanophosphonate: Synthesis of Phosphonocyanohydrin O-Phosphates
S
ynthesis of Phosp
y
honocyanoh
h
ydrin
O
-Pho
a
Department of Chemistry, Middle East Technical University, 06531 Ankara, Turkey
Fax +90(31)22103200; E-mail: asdemir@metu.edu.tr
Received 13 October 2008; revised 27 January 2009
drins and their rearrangement to cyanohydrin phos-
phates.10
Abstract: Cyanide ion catalyzed addition of acylphosphonates to
diethyl cyanophosphonate furnished phosphonocyanohydrin O-
phosphates in high yield. The reaction works via the phosphonate–
phosphate rearrangement, followed by the addition of diethyl
cyanophosphonate to the cyanohydrin phosphate anion.
In the present paper, we report the cyano-phosphorylation
of various alkyl and aryl phosphonates by their reaction
with stoichiometric amounts of diethyl cyanophosphonate
and substochiometric amounts of potassium cyanide. The
products can be further converted into various interesting
structures, such as functionalized amino phosphonic acids
and carboxylic acid derivatives.
Key words: phosphonocyanohydrins, diethyl cyanophosphonate,
addition reactions, acyl phosphonates, nucleophilic additions
Cyanohydrins and their trimethylsilyl ethers are versatile
intermediates in organic synthesis.1,2 Many methods have
been devised for the synthesis of these target compounds
in a racemic and enantioselective manner. The typical
method for their synthesis is the addition of a cyanide
source, in various forms, to the corresponding carbonyl
compounds.3 The source of cyanide determines the re-
spective type of the protecting group on hydroxy function-
ality, which is, most of the time, crucial for the success of
subsequent transformations. Since the instability of cy-
anohydrins and their trimethylsilyl ethers is sometimes
problematic for further transformations, the development
of a one-pot cyanation–O-protection reaction with a stable
protecting group has become desirable.4 In 1983, the one-
pot reaction of carbonyl compounds with diethyl cyano-
phosphonate (DEPC) in the presence of lithium diisopro-
pylamide was reported by Harusawa et al.5 Subsequently,
several catalytic asymmetric cyano-phosphorylation
methods were developed for aldehydes and prochiral ke-
tones.6 Recently, Baeza et al. reported a catalytic asym-
metric cyano-phosphorylation reaction using a chiral
aluminum catalyst7 with diethyl cyanophosphonate,
which is revealed as an excellent phosphorylating agent in
the asymmetric processes. There are several methods for
the transformation of aldehydes and ketones into racemic
cyanohydrin O-phosphates by their reaction with diethyl
cyanophosphonate.8 In our work, we applied the known
reaction of diethyl cyanophosphonate with carbonyls to
acylphosphonates.
For the investigation of the reaction of the diethyl cyano-
phosphonate with acylphosphonates 1, we planned to gain
direct and uncatalyzed access to phosphonocyanohydrin
O-phosphates 2 by using diethyl cyanophosphonate both
as a cyanide source and as an electrophile. Moreover, we
hoped that diethyl cyanophosphonate could supply a cat-
alytic amount of cyanide ion by decomposition in order to
provide cyanohydrin phosphate, which can subsequently
start the reaction. The formation of cyanohydrin phos-
phate, via phosphonate–phosphate rearrangement, and
followed by C-phosphonylation, should in turn form
phosphonocyanohydrin O-phosphates.
In the first reaction, dimethyl benzoylphosphonate (1e)
was reacted with diethyl cyanophosphonate at ambient
temperature in diethyl ether and monitored by TLC; no
product formation was observed. However, in the pres-
ence of catalytic quantities of potassium cyanide, ben-
zoylphosphonate 1e reacted slowly with diethyl
cyanophosphonate in diethyl ether to afford the desired
product 2e in a very low yield. The reaction was repeated
with various solvents and at various temperatures (data
not shown) and the best result was obtained with tetrahy-
drofuran.
When benzoylphosphonate 1e was reacted with diethyl
cyanophosphonate in the presence of catalytic quantities
of potassium cyanide in tetrahydrofuran, the desired (cy-
ano)(diethoxyphosphoryl)(phenyl)methyl dimethyl phos-
phate (2e) was obtained in 90% yield after purification by
column chromatography (Table 1, entry 5). The reaction
scope was studied using a variety of acylphosphonates
and the corresponding cyanohydrin O-phosphates were
synthesized in good to high yields (Table 1).
In recent years, we have published several papers on the
addition reactions of acylphosphonates.9 There are also
some publications related to the synthesis and reactions of
acylphosphonates in order to form phosphonocyanohy-
From the obtained products, only one compound of this
class 2a has been synthesized before in the reaction of
acetyl cyanide with pyrophosphites.11 Similar compounds
were also described by Gazizov et al.12 and Pudovik.13
SYNTHESIS 2009, No. 10, pp 1655–1658
Advanced online publication: 14.04.2009
x
x.
x
x
.
2
0
0
9
DOI: 10.1055/s-0029-1216634; Art ID: T18108SS
© Georg Thieme Verlag Stuttgart · New York

1656
A. S. Demir et al.
PAPER
All reactions were carried out in oven-dried Schlenk tubes with
magnetic stirring under a positive pressure of argon. Solvents were
freshly distilled under an argon atmosphere prior to use. Carboxylic
acids, trialkylphosphites and DEPC were purchased from Aldrich
and used as received. Acyl phosphonates were prepared according
to the literature procedures and purified by vacuum distillation.9
Thin-layer chromatography (TLC) was conducted on aluminum
sheets that were pre-coated with silica gel SIL G/UV254 from MN
GmbH & Co.; spots were visualized using UV light (254 nm) and/
or by staining with ninhydrin. Chromatographic separations were
performed using silica gel (MN-silica gel 60, 230–400 mesh). IR
measurements were performed on a Varian 1000 FTIR spectropho-
tometer. 1H and 13C NMR spectra were recorded on a Bruker
DPX400 NMR spectrometer. Chemical shifts (d) are reported in
parts per million (ppm) relative to the residual protons in the NMR
solvent (1H NMR: CHCl3, d = 7.24 ppm) and carbon resonance of
the solvent (13C NMR: CDCl3, d = 77.0 ppm). Elemental analyses
were performed using a LECO CHNS-932 instrument.
Table 1 Addition of Acylphosphonates to Diethyl Cyanophospho-
natea
PO(OR2)2
CN
O
O
O
OR2
OR2
KCN (cat.)
THF
P
R1
P
NC
OEt
+
R1
PO(OEt)2
OEt
O
1a–j
2a–j
Yield (%)
75
Entry
R1
R2
Product
2a
1
2
Me
Et
Me
Me
Me
Me
Me
Me
Me
Me
Me
Et
2b
2c
73
3
t-Bu
Cy
81
4
2d
2e
85
5
Ph
90
1-(Alkoxyphosphoryl)-1-cyanoalkyl Dialkyl Phosphates 2a–j;
General Procedure
6
4-MeC6H4
4-MeOC6H4
4-FC6H4
4-MeC6H4
Ph
2f
86
To a soln of acylphosphonate 1a–j (1 mmol) in anhyd THF (2 mL)
was added DEPC (1.52 mL, 1 mmol) under argon at r.t. Then, KCN
(2 mg) was added in one portion. The reaction was stirred at r.t. and
monitored by TLC (completed within 12–24 h). After the reaction
reached completion, THF was removed under reduced pressure and
the crude product was purified by flash column chromatography
(EtOAc).
7
2g
82
8
2h
2i
80
9
86
10
2j
88
a Reaction conditions: 1a–j (1 mmol), DEPC (1 mmol), KCN (cat.),
1-Cyano-1-(diethoxyphosphoryl)ethyl Dimethyl Phosphate (2a)
THF, r.t., 12–24 h.
Yellow oil; yield: 75%.
Presumably, the addition of the cyanide ion to the IR (KBr): 2990, 2256, 1435, 1270, 1028, 845, 590 cm–1.
1H NMR (400 MHz, CDCl3): d = 1.33 (m, 6 H), 1.97 (d, J = 14.7
Hz, 3 H), 3.89 (d, J = 6.5 Hz, 3 H), 3.92 (d, J = 6.5 Hz, 3 H), 4.07–
4.21 (m, 4 H).
13C NMR (100 MHz, CDCl3): d = 115.3, 69.6 (dd, J = 178.7, 9.3
Hz), 64.8 (d, J = 6.0 Hz), 64.6 (d, J = 6.0 Hz), 55.7 (d, J = 6.3 Hz),
55.1 (d, J = 6.5 Hz), 22.1, 16.0 (d, J = 6.7 Hz).
acylphosphonate forms the intermediate alkoxide, which
rearranges to the carbanion that in turn reacts with diethyl
cyanophosphonate in order to provide the product. The
proposed catalytic cycle is outlined in Scheme 1.
O
O
31P NMR (CDCl3): d = –5.3 (d, J = 32 Hz), 13.1 (d, J = 32 Hz).
NC
R1
R1
P(OR2)2
O
P(OR2)2
Anal. Calcd for C9H19NO7P2 (315.06): C, 34.29; H, 6.08; N, 4.44.
Found: C, 34.43; H, 6.25; N, 4.29.
O
1-Cyano-1-(diethoxyphosphoryl)propyl Dimethyl Phosphate
(2b)
Yellow oil; yield: 73%.
OPO(OR2)2
CN
R1
CN
IR (KBr): 2985, 2240, 1470, 1375, 1281, 1027, 835, 559 cm–1.
1H NMR (400 MHz, CDCl3): d = 1.16 (t, J = 7.6 Hz, 3 H), 1.33 (m,
6 H), 2.27 (m, 2 H), 3.89 (d, J = 2.9 Hz, 3 H), 3.91 (d, J = 2.9 Hz, 3
H), 4.16 (m, 4 H).
13C NMR (100 MHz, CDCl3): d = 114.2, 73.9 (dd, J = 175.4, 9.9
Hz), 64.7 (d, J = 6.1 Hz), 64.6 (d, J = 6.1 Hz), 55.5 (d, J = 7.0 Hz),
55.0 (d, J = 7.2 Hz), 29.7, 16.0 (d, J = 6.8 Hz), 8.42 (d, J = 5.2 Hz).
(R2O)2OPO CN
O
OEt
OEt
R1
P
P
CN
EtO OEt
O
Scheme 1
31P NMR (CDCl3): d = –5.0 (d, J = 32 Hz), 13.2 (d, J = 32 Hz).
In conclusion, we have developed a convenient, one-pot
procedure for preparing various polyfunctionalized cy-
anohydrins with the formation of a new C–P bond starting
from readily available acylphosphonates and diethyl cy-
anophosphonate under mild conditions in good to high
yields (73–90%). The general applicability of the reaction
with a range of acylphosphonate and diethyl cyanophos-
phonate was demonstrated.
Anal. Calcd for C10H21NO7P2 (329.22): C, 36.48; H, 6.43; N, 4.25.
Found: C, 36.35; H, 6.61; N, 4.14.
1-Cyano-1-(diethoxyphosphoryl)-2,2-dimethylpropyl Dimethyl
Phosphate (2c)
Yellow oil; yield: 81%.
IR (KBr): 2983, 2245, 1479, 1372, 1275, 1031, 837, 589 cm–1.
1H NMR (400 MHz, CDCl3): d = 1.21 (s, 9 H), 1.33 (t, J = 7.0 Hz,
6 H), 3.88 (d, J = 10.9 Hz, 3 H), 3.92 (d, J = 10.9 Hz, 3 H), 4.13–
4.21 (m, 4 H).
Synthesis 2009, No. 10, 1655–1658 © Thieme Stuttgart · New York

PAPER
Synthesis of Phosphonocyanohydrin O-Phosphates
1657
13C NMR (100 MHz, CDCl3): d = 114.0, 79.7 (dd, J = 169.3, 12.9
Hz), 64.7 (d, J = 5.8 Hz), 55.2 (d, J = 7.5 Hz), 55.1 (d, J = 7.0 Hz),
40.9, 25.8, 16.0.
31P NMR (CDCl3): d = –5.8 (d, J = 16 Hz), 12.6 (d, J = 16 Hz).
Hz), 64.4 (d, J = 5.9 Hz), 55.8 (d, J = 7.6 Hz), 55.5 (d, J = 7.3 Hz),
55.2, 16.0 (d, J = 6.4 Hz).
31P NMR (CDCl3): d = –5.3 (d, J = 48 Hz), 11.3 (d, J = 48 Hz).
Anal. Calcd for C15H23NO8P2 (407.29): C, 44.23; H, 5.69; N, 3.44.
Found: C, 44.35; H, 5.81; N, 3.55.
Anal. Calcd for C12H25NO7P2 (357.28): C, 40.34; H, 7.05; N, 3.92.
Found: C, 39.65; H, 7.19; N, 4.16.
(Cyano)(diethoxyphosphoryl)(4-fluorophenyl)methylDimethyl
Phosphate (2h)
Colorless oil; yield: 80%.
(Cyano)(cyclohexyl)(diethoxyphosphoryl)methyl Dimethyl
Phosphate (2d)
Yellow oil; yield: 85%.
IR (KBr): 2987, 2254, 1449, 1270, 1046, 808, 764 cm–1.
IR (KBr): 2990, 2260, 1465, 1284, 1048, 875 cm–1.
1H NMR (400 MHz, CDCl3): d = 1.23 (m, 6 H), 3.63 (d, J = 10.7
Hz, 3 H), 3.90 (d, J = 10.8 Hz, 3 H), 3.96–4.11 (m, 4 H), 7.08 (t,
J = 8.5 Hz, 2 H), 7.70 (m, 2 H).
13C NMR (100 MHz, CDCl3): d = 163.7 (d, J = 250 Hz), 129.7,
126.8, 115.7, 114.0, 74.4 (dd, J = 173.5, 10.8 Hz), 64.8 (d, J = 5.9
Hz), 64.6 (d, J = 6.0 Hz), 56.0 (d, J = 6.9 Hz), 55.7 (d, J = 7.0 Hz),
15.8 (m).
1H NMR (400 MHz, CDCl3): d = 1.17–1.35 (m, 12 H), 1.62–2.18
(m, 5 H), 3.88 (d, J = 3.8 Hz, 3 H), 3.91 (d, J = 3.9 Hz, 3 H), 4.12–
4.20 (m, 4 H).
13C NMR(100 MHz, CDCl3): d = 114.0, 76.7 (dd, J = 171.7, 11.7
Hz), 64.7 (d, J = 5.3 Hz), 63.4 (d, J = 5.5 Hz), 55.5 (d, J = 7.4 Hz),
55.1 (d, J = 7.3 Hz), 44.8, 27.3 (dd, J = 16.7, 3.6 Hz), 25.9, 25.6,
16.0 (m).
31P NMR (CDCl3): d = –5.2 (d, J = 49 Hz), 10.9 (d, J = 49 Hz).
31P NMR (CDCl3): d = –5.2 (d, J = 32 Hz), 12.8 (d, J = 32 Hz).
Anal. Calcd for C14H20FNO7P2 (395.26): C, 42.54; H, 5.10; F, 4.81;
N, 3.54. Found: C, 43.15; H, 5.34; F, 4.65; N, 3.23.
Anal. Calcd for C14H27NO7P2 (383.31): C, 43.87; H, 7.10; N, 3.65.
Found: C, 43.70; H, 7.21; N, 3.87.
(Cyano)(diethoxyphosphoryl)(m-tolyl)methyl Dimethyl Phos-
phate (2i)
(Cyano)(diethoxyphosphoryl)(phenyl)methyl Dimethyl Phos-
phate (2e)
Yellow oil; yield: 86%.
Colorless oil; yield: 90%.
IR (KBr): 2986, 2256, 1443, 1273, 1028, 847, 808 cm–1.
IR (KBr): 2987, 2260, 1446, 1280, 1050, 855 cm–1.
1H NMR (400 MHz, CDCl3): d = 1.23 (m, 6 H), 2.35 (s, 3 H), 3.60
(d, J = 2.9 Hz, 3 H), 3.86 (d, J = 3.0 Hz, 3 H), 3.90– 4.10 (m, 4 H),
7.23 (m, 1 H), 7.28 (m, 1 H), 7.50 (m, 2 H).
13C NMR (100 MHz, CDCl3): d = 137.3, 130.0, 129.6, 127.4, 126.7,
123.3, 113.2, 74.1 (dd, J = 173.6, 11.1 Hz), 63.6 (d, J = 5.6 Hz),
63.4 (d, J = 5.9 Hz), 54.9 (d, J = 7.0 Hz), 54.6 (d, J = 7.9 Hz), 20.4,
14.7 (m).
1H NMR (400 MHz, CDCl3): d = 1.19 (t, J = 7.0 Hz, 3 H), 1.24 (t,
J = 7.2 Hz, 3 H), 3.60 (d, J = 10.8 Hz, 3 H), 3.87 (d, J = 10.8 Hz, 3
H), 3.94–4.10 (m, 4 H), 7.40 (m, 3 H), 7.70 (m, 2 H).
13C NMR (100 MHz, CDCl3): d = 130.9, 130.2, 128.6, 127.2, 114.2,
75.0 (dd, J = 172.4, 11.0 Hz), 64.7 (d, J = 5.9 Hz), 64.5 (d, J = 5.9
Hz), 55.9 (d, J = 6.9 Hz), 55.7 (d, J = 7.1 Hz), 15.7 (m).
31P NMR (CDCl3): d = –4.7 (d, J = 48 Hz), 11.6 (d, J = 48 Hz).
31P NMR (CDCl3): d = –4.7 (d, J = 38 Hz), 11.7 (d, J = 38 Hz).
Anal. Calcd for C14H21NO7P2 (377.27): C, 44.57; H, 5.61; N, 3.71.
Found: C, 44.70; H, 5.75; N, 3.89.
Anal. Calcd for C15H23NO7P2 (391.29): C, 46.04; H, 5.92; N, 3.58.
Found: C, 46.27; H, 5.75; N, 3.78.
(Cyano)(diethoxyphosphoryl)(p-tolyl)methyl Dimethyl Phos-
phate (2f)
Cyano(diethoxyphosphoryl)(phenyl)methyl Diethyl Phosphate
(2j)
Colorless oil; yield: 86%.
Yellow oil; yield: 88%.
IR (KBr): 2986, 2260, 1446, 1274, 1020, 859, 763 cm–1.
IR (KBr): 2991, 2268, 1454, 1290 cm–1.
1H NMR (400 MHz, CDCl3): d = 1.20 (m, 6 H), 2.33 (s, 3 H), 3.59
(d, J = 10.8 Hz, 3 H), 3.87 (d, J = 10.8 Hz, 3 H), 3.93–4.10 (m, 4 H),
7.18 (d, J = 8.1 Hz, 2 H), 7.57 (dd, J = 8.2, 1.8 Hz, 2 H).
13C NMR (100 MHz, CDCl3): d = 140.4, 129.3, 127.8, 127.3, 114.3,
75.1 (dd, J = 178.0, 10.8 Hz), 64.7 (d, J = 5.9 Hz), 64.5 (d, J = 5.9
Hz), 55.9 (d, J = 6.9 Hz), 55.6 (d, J = 6.9 Hz), 21.2, 15.8 (m).
1H NMR (400 MHz, CDCl3): d = 1.23 (m, 12 H), 3.73–4.34 (m, 8
H), 7.39 (m, 3 H), 7.69 (m, 2 H).
13C NMR (100 MHz, CDCl3): d = 131.1, 130.2, 128.5, 127.5, 114.5,
74.5 (dd, J = 172.4, 11.0 Hz), 65.8 (d, J = 5.9 Hz), 64.6 (d, J = 5.9
Hz), 16.0 (m).
31P NMR (CDCl3): d = –4.7 (d, J = 48 Hz), 9.30 (d, J = 48 Hz).
31P NMR (CDCl3): d = –4.7 (d, J = 48 Hz), 11.7 (d, J = 48 Hz).
Anal. Calcd for C16H25NO7P2 (405.32): C, 47.41; H, 6.22; N, 3.46.
Found: C, 47.50; H, 6.23; N, 3.49.
Anal. Calcd for C15H23NO7P2 (391.29): C, 46.04; H, 5.92; N, 3.58.
Found: C, 46.27; H, 5.75; N, 3.78.
Supporting Information for this article is available online at
http://www.thieme-connect.com/ejournals/toc/synthesis.
(Cyano)(diethoxyphosphoryl)(4-methoxyphenyl)methyl
Dimethyl Phosphate (2g)
Colorless oil; yield: 82%.
IR (KBr): 2978, 2247, 1435, 1270, 1018, 850, 785 cm–1.
Acknowledgment
1H NMR (400 MHz, CDCl3): d = 1.24 (m, 6 H), 3.58 (d, J = 10.8
Hz, 3 H), 3.76 (s, 3 H), 3.88 (d, J = 10.6 Hz, 3 H), 3.92–4.09 (m, 4
H), 6.88 (d, J = 8.6 Hz, 2 H), 7.60 (d, J = 8.5 Hz, 2 H).
13C NMR (100 MHz, CDCl3): d = 161.1, 129.0 (d, J = 4.5 Hz),
122.4, 114.4, 113.9, 74.8 (dd, J = 187.0, 11.7 Hz), 64.6 (d, J = 6.1
The financial support from the Middle East Technical University,
Scientific and Technical Research Council of Turkey (TÜBITAK),
the Turkish Academy of Sciences (TÜBA), and the Turkish State
Planning Organization is gratefully acknowledged.
Synthesis 2009, No. 10, 1655–1658 © Thieme Stuttgart · New York

1658
A. S. Demir et al.
PAPER
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Synthesis 2009, No. 10, 1655–1658 © Thieme Stuttgart · New York