Synthesis of dichloromethylphosphonates

Article abstract of DOI:10.1080/10426500902719248

Efficient synthesis of O,O-dialkyl, O-alkyl-N,N-dialkylamido and N,N,N',N'-tetraalkyldiamido dichloromethylphosphonates via treatment of O,O-dialkyl, O-alkyl-N,N-dialkylamido, and N,N,N',N'-tetraalkyldiamido trichloromethylphosphonates with diethyl phosph

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Phosphorus, Sulfur, and Silicon
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Synthesis of
Dichloromethylphosphonates
Piotr Majewski a & Jacek F. Koszuk a
a Technical University of Łódź, Institute of Organic
Chemistry , Łódź, Poland
Published online: 26 Mar 2009.
To cite this article: Piotr Majewski & Jacek F. Koszuk (2009) Synthesis of
Dichloromethylphosphonates, Phosphorus, Sulfur, and Silicon and the Related
Elements, 184:4, 956-962, DOI: 10.1080/10426500902719248
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Phosphorus, Sulfur, and Silicon, 184:956–962, 2009
Copyright © Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500902719248
Synthesis of Dichloromethylphosphonates
Piotr Majewski and Jacek F. Koszuk
Technical University of Lꢀ o´dz´, Institute of Organic Chemistry, Lꢀ o´dz´,
Poland
Efficient synthesis of O,O-dialkyl, O-alkyl-N,N-dialkylamido and N,N,Nꢀ,Nꢀ-
tetraalkyldiamido dichloromethylphosphonates via treatment of O,O-dialkyl, O-
alkyl-N,N-dialkylamido, and N,N,Nꢀ,Nꢀ-tetraalkyldiamido trichloromethylphos-
phonates with diethyl phosphite in the presence of triethylamine in ethanol has
been described.
Keywords Dichloromethylphosphonates
INTRODUCTION
The chemistry of O,O-dialkyl, O-alkyl-N, N-dialkylamido, and
N,N,Nꢀ,Nꢀ-tetraalkyldiamido dihalogenomethylphosphonates has been
extensively investigated 30 years ago1,2,3a and later.3b,c These phos-
phonates have found wide application as starting materials for
the synthesis of functionalized 1-halogenomethylphosphonates,1−3
1,1-dihalogenoalkenes,2 and 1,2-epoxyalkanephosphonates.1 1,1-
Dihalogenophosphonates can be also readily transformed into the cor-
responding carbanions, which are the goal of carbon–carbon bond form-
ing strategy.2
Three general methods have been commonly used for the preparation
of O,O-dialkyl and N,N,Nꢀ,Nꢀ-tetraalkyldiamido dichloromethylphos-
phonates 2.
The Normant’s pioneering approach is based on the dechlorination
of 1,1,1-trichloromethylphosphonates 1 with n-buthyllithium/hexa-
methylphosphoramidate and subsequent quenching of the result-
ing dichloromethylphosphonate anion 5 with water or ethanol
Received 19 December 2007; accepted 29 February 2008.
Dedicated to Professor Marian Mikolꢀajczyk from the CBMiM PAN in Lꢀ o´dz´, Poland,
on the occasion of his 70th birthday.
Address correspondence to Piotr Majewski, Technical University of Lꢀ o´dz´, Institute
˙
of Organic Chemistry, Zeromskiego 116, 90-924 Lꢀ o´dz´, Poland. E-mail: biotr.majewski@
p.lodz.pl
956

Synthesis of Dichloromethylphosphonates
957
SCHEME 1
(Scheme 1a).5a The second procedure relies on metallation of the
chloromethylphosphonates 3 with butyllithium4,5 followed by chlori-
nation of the obtained lithium chloromethylphosphonate 4 with carbon
tetrachloride (Scheme 1b).
The third method involves the standard preparation of the phos-
phorus trichloride/aluminum chloride/chloroform complex 6 and its de-
composition with the selected alcohol or secondary amine, respectively
(Scheme 2).6
SCHEME 2
A
few other additional procedures for the synthesis of
N,N,Nꢀ,Nꢀ-tetraalkyldiamido methylphosphonates and O,O-dialkyl
alkylphosphonates have been reported.7−13 For example, N,N,NꢀNꢀ-
tetraalkyldiamido methylphosphonate has been obtained by aminoly-
sis of chlorobis(dialkylamine)dichloromethylenephosphorane7,8 and its
precursors,9,10 whereas O,O-dialkyl dichloromethylphosphonates have
been produced from O,O-dialkyl trichloromethylphosphonates and di-
ethyl phosphite in the presence of stoichiometric amounts of ethanol14
(Scheme 3).
In this article, we describe an efficient and general proce-
dure for the preparation of O,O-dialkyl, O-alkyl-N, N-dialkylamido,
and N, N, Nꢀ, Nꢀ-tetraalkyldiamido dichloromethyl-phosphonates using
mild reaction conditions and readily available starting materials.

958
P. Majewski and J. F. Koszuk
SCHEME 3
RESULTS AND DISCUSSION
From the synthesis of O,O-dialkyl dichloromethylphophonates, us-
ing diethyl phosphite, triethyl amine, and stoichiometric amounts
of ethanol, we assumed that this method can be success-
fully used for the synthesis of O-ethyl-N, N-dialkylamido and
N, N, Nꢀ, Nꢀ-tetraalkyldiamido dichloromethylphosphonates 2 accord-
ing to Scheme 4.
SCHEME 4
When O-alkyl-N, N-dialkylamido and N, N, Nꢀ, Nꢀ-tetraalkyldiamido
trichloromethyl-phosphonates 1f–i were treated with dialkyl phosphite
in the presence of triethylamine and stoichiometric amounts of ethanol
in a neutral solvent, the corresponding dichloromethyl-phosphonates
were produced in rather low yield. However, when similar reac-
tions were carried out in ethanol at ambient temperature, the yields
of the O-alkyl-N, N-dialkylamido and N, N, Nꢀ, Nꢀ-tetraalkyldiamido
dichloromethylphosphonates 2f–i were high to excellent.
The transformation of O,O-dialkyl trichloromethylphosphonates
into O,O-dialkyl dichloromethylphosphonates 2a–d was also very ef-
fective following the same protocol. The dechlorination reaction was
readily monitored by 31P NMR. The reaction products were isolated
by distillation under reduced pressure. The structures of the new com-
pounds were confirmed by IR and NMR spectroscopy. All of them have
IR (film) absorption band characteristic for a P O moiety: broad band
1
at 1280 cm−1. Their H NMR spectra (CDCl3) showed characteristic
doublets at δ = 5.65–5.75 ppm (2JPH = 1 Hz) for the methine proton of
CHCl2 moiety (see the Experimental section).

Synthesis of Dichloromethylphosphonates
959
O,O-dialkyl, O-alkyl-N, N-dialkylamido, and N, N, Nꢀ, Nꢀ-tetraalkyl-
diamido dichloro-methylphosphonates (2a–d, f–i, and1f) gave satisfac-
tory elemental analyses (C
0,3%, H
0,2%). Yields and physical
constants are presented in Table I.
As shown in Table I, O,O-dimethyl dichloromethylphosphonate (2e)
could not be obtained by the present method, probably due to the ex-
tensive dealkylation of the substrate 1e as well as of the potential
product 2e. In all other cases, no traces of the dealkylation reaction of
the substrates and the products were observed.
CONCLUSION
Here we have reported a general synthetic procedure providing O,O-
dialkyl, O-alkyl-N, N-dialkylamido, and N, N, Nꢀ, Nꢀ-tetraalkyldiamido
dichloromethylphosphonates under mild conditions in high to excellent
yields.
EXPERIMENTAL
Organic solvents and reagents were purified by commonly used
procedures.19 IR spectra were recorded with a Specord M-80 spec-
1
trophotometer. 1H NMR (250 MHz) and 31P{ H} NMR (101 MHz) spec-
tra were recorded with a Bruker DPX-250 spectrometer with TMS as
1
an internal standard for H and 85% H3PO4 as an external standard
for 31P. 31P NMR spectra were recorded using broadband proton decou-
1
pling. All chemical shifts (δ) are reported in ppm. In the case of H,
the residual solvent peak was used as the internal standard (CHCl3
at 7.26 ppm). Coupling constants (J) are reported in Hz. O,O-Dialkyl
trichloromethyl-phosphonates have been prepared according to litera-
ture procedures.11,15−17
Physical and analytical data of the phosphonates 2 are presented in
Table I.
Reaction of O,O-Dialkyl-, O-Alkyl-N,N-dialkylamido-,
N,N,Nꢀ,Nꢀ-Tetraalkylamido-1,1,1-trichloromethylphosphonates
1a–i with Diethylphosphite: General Procedure
To a solution of the dialkyl 1,1,1-trichloromethylphosphonate 1 (0.1
mol) and triethylamine (12.1 g, 0.12 mol) in ethanol (50 mL), diethyl
phosphite (16.5 g, 0.12 mol) was added dropwise at 20◦C. The mix-
ture was kept at room temperature, and the progress of the reaction
was monitored by 31P NMR spectroscopy. After six days, or longer if

960

Synthesis of Dichloromethylphosphonates
961
necessary, the solvent from the reaction mixture was evaporated under
reduced pressure, and the residue was diluted with chloroform (100
mL). The solution was washed with water (2 × 50 mL), dried over
sodium sulfate, and the solvent was removed in vacuo. The residue
was purified by distillation under reduced pressure after separating
triethylphosphate at 60◦C/0.8 mm Hg.
O,O-Di-n-propyl-1,1-dichloromethylphosphonate (2b)
1
20.5 g (81%); b.p. 100–101◦C/0.8 mm Hg. H NMR (CDCl3): δ = 1.0 (t,
3
3
3JHH = 7 Hz, 6H), 1.75 (sextet, JHH = 7 Hz, 4H), 4.20 (m, JHH = 7,
3JPH = 7 Hz, 4H), 5.70 (d, 2JPH = 1 Hz, 1H). 31P{ H} NMR (CDCl3): δ =
1
10.0. IR (CC14): ν(P=O) 1280 cm−1
.
O-Ethyl-N,N-dimethyl-1,1-dichloromethylphosphonate (2f)
1
15.8 g (72%); b.p. 92–93◦C/0.5 mm Hg. H NMR (CDCl3): δ = 1.35 (t,
3JHH = 7 Hz, 3H), 2.78 (d, 3JPH = 8.7 Hz, 6H), 4.25 (m, 3JHH = 7, 3JPH
=
2
1
7 Hz, 2H), 5.75 (d, JPH = 1 Hz, 1H). 31P{ H} NMR (CDCl3): δ = 17.0.
Anal. Calcd. for C5H12Cl2NOP: C 27.29, H 5.49. Found: C 27.10, H
5.30%.
O-Ethyl-N,N-diethyl-1,1-dichloromethylphosphonate (2g)
1.2 g (62%); b.p. 100◦C/0.6 mm Hg. 1H NMR (CDCl3): δ = 1.10 (t, 3JHH
=
3
3
7 Hz, 6H), 1.28 (t, JHH = 7 Hz, 3H), 3.05 (m, 4H), 3.96 (q, JHH = 7,
2
1
3JPH = 7 Hz, 2H), 5.65 (d, JPH = 1 Hz, 1H). 31P{ H} NMR (CDCl3):
18.2. Anal. Calcd. for C7H16Cl2NO2P: C 33.89, H 6.50. Found C 33.62,
H 6.32%.
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962
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3
Hg. 1H NMR (CDCl3): δ = 1.31 (t, JHH = 7 Hz, 3H), 2.88 (d, JPH = 8.5 Hz, 6H),
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