7498 J. Org. Chem. 2010, 75, 7498–7501 Published on Web 10/06/2010 DOI: 10.1021/jo101743e
r 2010 American Chemical Society
pubs.acs.org/joc
Lanthanide Amides [(Me3Si)2N]3Ln(μ-Cl)Li(THF)3
Catalyzed Hydrophosphonylation of Aryl Aldehydes
Qingmao Wu, Jun Zhou, Zhigang Yao, Fan Xu,* and
Qi Shen*
Key Laboratory of Organic Synthesis, College of Chemistry,
Chemical Engineering and Materials Science,
Soochow University, Suzhou 215123, China
*xufan@suda.edu.cn;qshen@suda.edu.cn
Received September 5, 2010
A highly efficient method for the synthesis of R-hydroxy
phosphonates via lanthanide amides [(Me3Si)2N]3Ln-
( μ-Cl)Li(THF)3 catalyzed hydrophosphonylation of aro-
matic aldehydes was developed. The reactions produced
the products in excellent yields in the presence of 0.1 mol%
[(Me3Si)2N]3La( μ-Cl)Li(THF)3 at room temperature with-
in 5 min. The existence of LiCl in the catalyst was a key
factor affecting the catalytic activity. Themechanism for the
process of high efficiency was proposed.
R-Hydroxy phosphonate exists as an important structural
unit inmany biologically active compounds which have been
widely used as pesticides, antibiotics, anticancer drugs, anti-
viral agents, enzyme inhibitors, and so on.1 Alternative
methods such as reduction of keto phosphonates,2 R-hydrox-
ylation of alkyl phosphonates,3 and addition of trialkyl
phosphites to aldehydes4 have been utilized for the synthesis
of R-hydroxy phosphonates. Besides these pathways, the
addition of dialkyl phosphites to aldehydes, known as the
Pudovik reaction,5 is undoubtedly the most straightforward
and atom-economical one toR-hydroxy phosphonates. How-
ever, the Pudovik reaction cannot proceed spontaneously
without heating in the absence of catalyst. Many research
groups dedicated their efforts to develop highly active cata-
lysts for this reaction in recent years. As a consequence, some
catalysts or promoters, includingmetal oxides (such asMgO6
and Al2O3
7), Lewis bases8 (such as Et3N,
9 pyridine,10 and
TMG11),Bronstedbases (suchasEtONa12 andTi(OiPr)4
13,7b),
and some others (such as KF14 and MoO2Cl2
15), were found
to be effective for this transformation. In addition, several
examples of the reaction under thermal noncatalyzed
conditions16 were also reported. It came to our notice that
most of these systems require relatively harsh reaction condi-
tions, such as high temperature (above 100 �C), long time
(over 1 h), and/or high catalyst loading (more than 10mol%).
Moreover, the yields were not always good and in some
instances the target products may cleave and regenerate
the starting raw materials.12,16b,17 More recently, to meet
the growing demand for enantiomerically pure materials,
the asymmetric synthesis of R-hydroxy phosphonates has
been greatly developed18 while the methods reported for the
(1) (a) Hilderbrand, R. L. The Role of Phosphonates in Living Systems;
CRC: Boca Raton, FL, 1983. (b) Engel, R. Handbook of Organophosphorus
Chemistry; Marcel Dekker: New York, 1992. (c) Szyma�nska, A.; Szymczak,
M.; Boryski, J.; Stawi�nski, J.; Kraszewski, A.; Collu,G.; Sanna,G.;Giliberti,
G.; Loddo, R.; Colla, P. L. Bioorg. Med. Chem. 2006, 14, 1924. (d) Shi, D.;
Sheng, Z.; Liu, X.; Wu, H. Heteroatom Chem. 2003, 14, 266. (e) Ganzhorn,
A. J.; Hoflack, J.; Pelton, P. D.; Strasser, F.; Chanal, M.; Piettre, S. R.
Bioorg. Med. Chem. 1998, 6, 1865. (f) Frechette, R. F.; Ackerman, C.; Beers,
S.; Look, R.; Moore J. Bioorg. Med. Chem. Lett. 1997, 7, 2169. (g) Patel,
D. V.; Rielly-Gauvin, K.; Ryono, D. E.; Free, C. A.; Rogers, W. L.; Smith,
S. A.; DeForrest, J. M.; Oehl, R. S.; Petrillo, E. W. J. Med. Chem. 1995, 38,
4557. (h) Stowasser, B.; Budt, K.; Jian-Qi, L.; Peyman, A.; Ruppert, D.
Tetrahedron Lett. 1992, 33, 6625. (i) Patel, D. V.; Rielly-Gauvin, K.; Ryono,
D. E. Tetrahedron Lett. 1990, 31, 5587.
(2) (a) Zhang, W.; Shi, M. Chem. Commun. 2006, 1218. (b) Nesterov,
V. V.; Kolodyazhnyi, O. I.Russ. J. Gen. Chem. 2006, 76, 1022. (c) Creary, X.;
Geiger, C. C.; Hilton, K. J. Am. Chem. Soc. 1983, 105, 2851. (d) Nesterov,
V. V.; Kolodyazhnyi, O. I. Tetrahedron: Asymmetry 2006, 17, 1023. (e)
Nesterov, V. V.; Kolodyazhnyi, O. I. Russ. J. Gen. Chem. 2005, 75, 1161. (f)
Meier, C.; Laux,W. H. G. Tetrahedron: Asymmetry 1995, 6, 1089. (g)Meier,
C.; Laux, W. H. G.; Bats, J. W. Liebigs Ann. 1995, 1963. (h) Meier, C.; Laux,
W.H.G.Tetrahedron 1996, 52, 589. (i)Meier, C.; Laux,W.H.G.; Bats, J.W.
Tetrahedron: Asymmetry 1996, 7, 89. (j) Ord�o~nez, M.; de la Cruz, R.;
Fern�andez-Zertuche, M. M.; Mu~noz-Hern�adez, M. A. Tetrahedron: Asym-
metry 2002, 13, 559.
(3) (a) Cristau, H.; Pirat, J.; Drag, M.; Kafarski, P. Tetrahedron Lett.
2000, 41, 9781. (b) Pogatchnik, D.M.;Wiemer, D. F.TetrahedronLett. 1997,
38, 3495. (c) Skropeta, D.; Schmidt, R. R.Tetrahedron: Asymmetry 2003, 14,
265.
(4) (a)Nakanishi, K.;Kotani, S.; Sugiura,M.;Nakajima,M.Tetrahedron
2008, 64, 6415. (b) Azizi, N.; Saidi, M. R. Phosphorus, Sulfur Silicon Relat.
Elem. 2003, 178, 1255. (c) Heydari, A.; Arefi, A.; Khaksar, S.; Tajbakhsh,M.
Catal. Commun. 2006, 7, 982. (d) Goldeman,W.; Soroka,M. Synthesis 2006,
3019. (e) Thottempudi, V.; Chung, K. Bull. Korean Chem. Soc. 2008, 29,
1781.
(5) Pudovik, A. N.; Konovalova, I. V. Synthesis 1979, 81.
(6) (a) Kaboudin, B. Tetrahedron Lett. 2003, 44, 1051. (b) Kaboudin, B.
Tetrahedron Lett. 2000, 41, 3169.
(7) (a) Texier-Boullet, F.; Foucaud, A. Synthesis 1982, 916. (b) Jung,
M. E.; Cordova, J.; Murakami, M. Org. Lett. 2009, 11, 3882.
(8) (a) Kaim, L. E.; Gaultier, L.; Grimaud, L.; Santos, A.D. Synlett 2005,
2335. (b) Gancarz, R. Tetrahedron 1995, 51, 10627.
(9) (a) Taylor, W. P.; Zhang, Z.; Widlanski, T. S. Bioorg. Med. Chem.
1996, 4, 1515. (b) Cristau, H.; Pirat, J.; Virieux, D.;Monbrun, J.; Ciptadi, C.;
Bekro, Y. J. Organomet. Chem. 2005, 690, 2472.
(10) Li, C.; Yuan, C. Tetrahedron Lett. 1993, 34, 1515.
(11) (a) Simoni, D.; Rondanin, R.;Morini, M.; Baruchello, R.; Invidiata,
F. P. Tetrahedron Lett. 2000, 41, 1607. (b) Simoni, D.; Invidiata, F. P.;
Manferdini, M.; Lampronti, I.; Rondanin, R.; Roberti, M.; Pollini, G. P.
Tetrahedron Lett. 1998, 39, 7615.
(12) Keglevich, G.; Sipos, M.; Takacs, D.; Greiner, I.Heteroatom Chem.
2007, 18, 226.
(13) Yokomatsu, T.; Yamagishi, T.; Shibuya, S. J. Chem. Soc., Perkin
Trans. 1 1997, 1527.
(14) (a) Texier-Boullet, F.; Foucaud, A. Synthesis 1982, 2, 165. (b) Li, Z.;
Sun, H.;Wang, Q.; Huang, R.Heteroatom Chem. 2003, 14, 384. (c) Villemin,
D.; Racha, R. Tetrahedron Lett. 1986, 27, 1789. (d) Sebti, S.; Rhihil, A.;
Saber, A.; Laghrissi, M.; Boulaajaj, S. Tetrahedron Lett. 1996, 37, 3999.
(15) de Noronha, R. G.; Costa, P. J.; Romao, C. C.; Calhorda, M. J.;
Fernandes, A. C. Organometallics 2009, 28, 6206.
(16) (a) Tsai, H.; Lin, K.; Ting, T.; Burton, D. J. Helv. Chim. Acta 1999,
82, 2231. (b)Kharasch,M. S.;Mosher, R.A.; Bengelsdorf, I. S. J.Org. Chem.
1960, 25, 1000.
(17) Gancarz, R.; Gancarz, I.; Walkowiak, U. Phosphorus, Sulfur Silicon
Relat. Elem. 1995, 104, 45.
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J. Org. Chem. Vol. 75, No. 21, 2010 7499
Wu et al. JOCNote
stereoselective hydrophosphonylation of aldehydes usually
involve high catalyst loading. Therefore, the further develop-
ment of novel catalysts and relevant processes of high efficiency
for the synthesis of R-hydroxy phosphonate as valuable small
molecule still remains of great interest.
Homoleptic bis(trimethylsilyl)amides of lanthanides
Ln[N(SiMe3)2]3
19 have been found to be efficient catalysts
for a series of intermolecular or intramolecular reactions,
including the Tishchenko reaction,20 amidation,21 monoad-
dition of terminal alkynes to nitriles,22 coupling reaction of
isocyanides with terminal alkynes,23 and dimerization of
terminal alkynes.24 They also show high activity as catalysts
for versatile hydroelementation processes such as hydrosilyla-
tion,25 hydroboration,26 hydroamination,20b,27 hydrophos-
phination,28 and hydroalkoxylation.29 The tetracoordinate
lanthanide amides [(Me3Si)2N]3Ln( μ-Cl)Li(THF)3,
30 a
chloride-bridged “ate” complex derived from Ln[N(SiMe3)2]3,
also work well as catalysts for aldol condensation,31 MMA
polymerization,30c,d aza-Henry reaction,32 and guanylation of
amines.33 Although [(Me3Si)2N]3Ln(μ-Cl)Li(THF)3 is more
readily available than Ln[N(SiMe3)2]3 from the viewpoint of
the syntheticmethod, the applicationof the former as an efficient
catalyst is comparatively limited. In some instances reported, the
catalytic activities of the tricoordinate Ln[N(SiMe3)2]3 and
tetracoordinate [(Me3Si)2N]3Ln(μ-Cl)Li(THF)3 were com-
pared with each other. The results indicated that the existence
of LiCl in [(Me3Si)2N]3Ln( μ-Cl)Li(THF)3 may sometimes
31,32
improve the activity of Ln[N(SiMe3)2]3 while at other times
33
produce the opposite effect.
In continuation of our previous studies on lanthanide-
catalyzed carbon-nitrogen bond-forming reactions,34 we
investigated the effectiveness of lanthanide amides as cata-
lysts for the carbon-phosphorus bond-forming reactions.
Herein, the paper presents a highly efficient process afford-
ing R-hydroxy phosphonates by the lanthanide amides-
catalyzed Pudovik reaction.
The addition of diethyl phosphite to benzaldehyde to
afford diethyl [hydroxy(phenyl)methyl]phosphonate was
used as themodel reaction in our initial screening of potential
lanthanide catalysts. As shown inTable 1, typical Lewis acid-
type compounds such as lanthanum trihalides (LaX3, X =
Cl, Br, I) and ytterbium triflate [Yb(OTf)3] cannot initiate
the reaction with the catalyst loading of 20 mol % (entries
1-4), indicating that the Lewis acidity of the lanthanide
compounds was not decisive in catalyzing this reaction. In
strong contrast, homoleptic lanthanum amide La[N(SiMe3)2]3
catalyzed the reaction with high efficiency. The product was
obtained in 63%yieldwith 0.5mol%La[N(SiMe3)2]3 at 25 �C
for 5min (entry 5). However, no desired product was observed
when the catalyst loadingwasdecreased to 0.1mol%(entry 6).
To our delight, the tetracoordinate lanthanum amide
[(Me3Si)2N]3La( μ-Cl)Li(THF)3 exhibited the catalytic activ-
ity that was still superior to that of tricoordinate lanthanum
amide La[N(SiMe3)2]3. The utility of 0.5 mol % of [(Me3Si)2-
N]3La( μ-Cl)Li(THF)3 gave the product in an excellent 96%
yield within 5min (entry 7). Optimization studies revealed that
decreasing the catalyst loading to 0.1 mol % kept the yield at
92% (entry 8). Further decreased catalyst loading of 0.05 mol
% led to a dramatically lowered yield of 43% (entry 9).
Because [(Me3Si)2N]3La(μ-Cl)Li(THF)3 can be regarded as
a solvated adduct of La[N(SiMe3)2]3 andLiCl, anhydrous LiCl
was tried alone to verify whether it can act as a catalyst inde-
pendently. No product was detected after 48 h (entry 10).
Besides, the use of the mixture of La[N(SiMe3)2]3 and
TABLE 1. Catalysts Screening for the Reaction of Benzaldehyde with
Diethyl Phosphitea
entry catalyst loading (mol %) time yield (%)
1 LaCl3 2.0 12 h 0
2 LaBr3 2.0 12 h 0
3 LaI3 2.0 12 h 0
4 Yb(OTf)3 2.0 6 h 0
5 La[N(SiMe3)2]3 0.5 5 min 63
6 La[N(SiMe3)2]3 0.1 5 min 0
7 [(Me3Si)2N]3La(μ-Cl)Li(THF)3 0.5 5 min 96
8 [(Me3Si)2N]3La(μ-Cl)Li(THF)3 0.1 5 min 92
9 [(Me3Si)2N]3La(μ-Cl)Li(THF)3 0.05 5 min 43
10 LiCl 1.0 48 h 0
aReactions were performed with 1 mmol of PhCHO and 1.2 mmol of
HOP(OEt)2 in 1 mL of toluene at 25 �C.
(18) (a)Merino, P.;Marqu�es-L�opez, E.; Herrera, R. P.Adv. Synth. Catal.
2008, 350, 1195. (b) Yang, F.; Zhao, D.; Lan, J.; Xi, P.; Yang, L.; Xiang, S.;
You, J. Angew. Chem., Int. Ed. 2008, 47, 5646. (c) Suyama, K.; Sakai, Y.;
Matsumoto, K.; Saito, B.; Katsuki, T.Angew. Chem., Int. Ed. 2009, 48, 1. (d)
Abell, J. P.; Yamamoto, H. J. Am. Chem. Soc. 2008, 130, 10521. (e)
Uraguchi, D.; Ito, T.; Ooi, T. J. Am. Chem. Soc. 2009, 131, 3836.
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Belot, J. A. Inorg. Chem. 2001, 40, 5292. (b) Bradley, D. C.; Ghotra, J. S.;
Hart, F.A. J. Chem. Soc., DaltonTrans. 1973, 1021. (c) Alyea, E. C.; Bradley,
D. C.; Copperthwaite, R. G. J. Chem. Soc., Dalton Trans. 1972, 1580. (d)
Andersen, R. A.; Templeton, D. H.; Zalkin, A. Inorg. Chem. 1978, 17, 2317.
(e) Brady, E. D.; Clark, D. L.; Gordon, J. C.; Hay, P. J.; Keogh, D.W.; Poli,
R.; Scott, B. L.; Watkin, J. G. Inorg. Chem. 2003, 42, 6682.
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1569. (b) B€urgstein, M. R.; Berberich, H.; Roesky, P. W. Chem.;Eur. J.
2001, 7, 3078. (c) Chen, Y.; Zhu, Z.; Zhang, J.; Shen, J.; Zhou, X. J.
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301.
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Takaki, K. Chem. Commun. 2005, 634. (b) Komeyama, K.; Sasayama, D.;
Kawabata, T.; Takehira, K.; Takaki, K. J. Org. Chem. 2005, 70, 10679.
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Chem. 2005, 70, 7260. (b)Nishiura,M.; Hou, Z.;Wakatsuki, Y.; Yamaki, T.;
Miyamoto, T. J. Am. Chem. Soc. 2003, 125, 1184. (c) Komeyama, K.;
Takehira, K.; Takaki, K. Synthesis 2004, 1062.
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Y. K.; Livinghouse, T.; Bercaw, J. E. Tetrahedron Lett. 2001, 42, 2933. (c)
Kim, Y. K.; Livinghouse, T.; Horino, Y. J. Am. Chem. Soc. 2003, 125, 9560.
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2003, 22, 4630.
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Anorg. Allg. Chem. 1995, 621, 837. (b) Edelmann, F. T.; Steiner, A.; Stalke,
D. Polyhedron 1994, 13, 539. (c) Zhou, S.; Wang, S.; Yang, G.; Liu, X.;
Sheng, E.; Zhang, K.; Cheng, L.; Huang, Z. Polyhedron 2003, 22, 1019. (d)
Xie, M.; Liu, X.; Wang, S.; Liu, L.; Wu, Y.; Yang, G.; Zhou, S.; Sheng, E.;
Huang, Z. Chin. J. Chem. 2004, 22, 678. (e) Sheng, E.; Wang, S.; Yang, G.;
Zhou, S.; Cheng, L.; Zhang, K.; Huang, Z. Organometallics 2003, 22, 684.
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2007, 72, 6763.
(34) (a) Xu, F.; Luo, Y.; Deng, M.; Shen, Q. Eur. J. Org. Chem. 2003,
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7500 J. Org. Chem. Vol. 75, No. 21, 2010
JOCNote Wu et al.
anhydrous LiCl in 1:1 ratio in THF as catalyst failed to
produce the same effect with [(Me3Si)2N]3La(μ-Cl)Li-
(THF)3. The result indicated that the combination manner
of La[N(SiMe3)2]3 with LiCl in crystalline [(Me3Si)2N]3-
La( μ-Cl)Li(THF)3 may be a key factor affecting its cata-
lytic ability. Then, the reaction conditions were selected as
0.1 mol % of [(Me3Si)2N]3Ln(μ-Cl)Li(THF)3 at 25 �C for
5 min for the following studies.
Next, a series of lanthanide amides were used to assess the
influence of central metal on the activity and the results are
shown in Table 2. It was found that the decrease in the Ln(III)
ionic radii from the light rare earth La to heavy rare earth
Er andY has little influence on the reaction and the high yields
above 90% were obtained. When [(Me3Si)2N]3Yb(μ-Cl)-
Li(THF)3 was used, a slightly decreased yield of 82% was
observed. So, the amide complexofLa, the largestmetal among
those tested, was chosen as a representative lanthanide source
for carrying out the following studies.
Considering the obvious difference in the activity pre-
sented between La[N(SiMe3)2]3 and [(Me3Si)2N]3La( μ-Cl)-
Li(THF)3, a new question arose if LiCl is the best partner of
La[N(SiMe3)2]3 in improving the activity. It was known that
[(Me3Si)2N]3Ln( μ-Cl)Li(THF)3 can be formed in situ by the
metathesis reaction of LnCl3 with 3 equiv of LiN(SiMe3)2 in
THF.30c-e To learn more about the influence of alkali metal
ion and halide ion on the reaction, themodel reaction with in
situ formed tetracoordinate lanthanumamides, generated by
the reaction of lanthanum trihalides with silylamides of
sodium or lithium, as catalysts was performed. The results
are presented in Table 3. As we expected, the in situ formed
[(Me3Si)2N]3La( μ-Cl)Li(THF)3 showed the same activity as
that of prepared [(Me3Si)2N]3La( μ-Cl)Li(THF)3 under the
standard reaction conditions. However, either changing
Cl to Br and I or changing Li to Na led to a decrease of the
yield. For example, the utility of LaI3 instead of LaCl3 gave a
yield of 14% (entry 3) while using NaN(SiMe3)2 instead of
LiN(SiMe3)2 provided an 18% yield (entry 4). The catalyst
generated from NaN(SiMe3)2 and LaI3 failed to give the
desired product (entry 5).
With the optimum reaction conditions in hand, the scope
of the reaction was explored to various aromatic aldehydes
and dialkyl phosphites. As shown in Table 4, all the reactions
proceeded smoothly and quickly affording the correspond-
ing R-hydroxy phosphonates in excellent yields (91-97%) at
room temperature within 5min. The reactionwas general for
aromatic aldehydes bearing substitutions at ortho-, meta-,
and para-positions and tolerates both electron-deficient
aldehydes and those that are electron rich. Heteroatoms
either in the functional groups of the benzene ring or in
heteroaromatics such as furan had no influence on the
reaction. Dialkyl phosphites with different steric hindrances
underwent the reaction giving the yields with little difference.
The results suggest that [(Me3Si)2N]3La( μ-Cl)Li(THF)3 is
highly active in catalyzing the hydrophosphonylation of
aromatic aldehydes, regardless of electronic effects or steric
effects of the substrates.
According to the distinctive properties of lanthanide
amides, the proposedmechanism (Scheme 1) for the Pudovik
reaction may involve rapid deprotonation of the dialkyl
phosphite, which may exist in its tautomeric form as the
phosphonate, releasing amine and forming the intermediate 5,
which is most probably the catalytically active species. 5 then
reacts as a nucleophile toward the carbonyl carbon atoms of
the aldehyde to generate the target R-hydroxy phosphonate.
The superiority in the catalytic ability of [(Me3Si)2N]3-
Ln(μ-Cl)Li(THF)3 over Ln[N(SiMe3)2]3 may be accounted
for by two possibilities. First, it has been found that the Ln-N
bond lengths in [(Me3Si)2N]3Ln(μ-Cl)Li(THF)3 are longer
than those found in Ln[N(SiMe3)2]3. For example, the average
Nd-N bond distance of 2.336 A˚30b in [(Me3Si)2N]3Nd-
( μ-Cl)Li(THF)3 is longer than the Nd-N bond length of
2.29 A˚19d found in Nd[N(SiMe3)2]3, and the average Sm-N
TABLE 2. The Influence of Lanthanide Metal on the Reactiona
Ln =
Y La Nd Sm Er Yb
yield (%) 93 93 94 92 90 82
aReactions were performed with 1 mmol of PhCHO and 1.2 mmol of
HOP(OEt)2 in 1 mL of toluene at 25 �C for 5 min.
TABLE 3. The Influence of Alkali Metals and Halogens on the React
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