N -BuLi as a highly efficient precatalyst for hydrophosphonylation of aldehydes and unactivated ketones

Article abstract of DOI:10.1021/ol5030713

It was found for the first time that organic alkali metal compounds serve as highly efficient precatalysts for the hydrophosphonylation reactions of aldehydes and unactivated ketones with dialkyl phosphite under mild conditions. For ketone substrates, a reversible reaction was observed, and the influence of catalyst loading and reaction temperature on the reaction equilibrium was studied in detail. Overall, the hydrophosphonylation reactions catalyzed by 0.1 mol % n-BuLi were completed within 5 min for a broad range of substrates and generated a series of α-hydroxy phosphonates in high yields.

Full text of DOI:10.1021/ol5030713

Letter
pubs.acs.org/OrgLett
n‑BuLi as a Highly Efficient Precatalyst for Hydrophosphonylation of
Aldehydes and Unactivated Ketones
Chengwei Liu,† Yu Zhang,† Qinqin Qian,† Dan Yuan,*,† and Yingming Yao*,†
†Key Laboratory of Organic Synthesis of Jiangsu Province, College of Chemistry, Chemical Engineering and Materials Science, Dushu
Lake Campus, Soochow University, Suzhou, 215123, People’s Republic of China
S
* Supporting Information
ABSTRACT: It was found for the first time that organic alkali
metal compounds serve as highly efficient precatalysts for the
hydrophosphonylation reactions of aldehydes and unactivated
ketones with dialkyl phosphite under mild conditions. For
ketone substrates, a reversible reaction was observed, and the
influence of catalyst loading and reaction temperature on the
reaction equilibrium was studied in detail. Overall, the hydrophosphonylation reactions catalyzed by 0.1 mol % n-BuLi were
completed within 5 min for a broad range of substrates and generated a series of α-hydroxy phosphonates in high yields.
ince organic phosphoric compounds play an important role
in organometallic, coordination, and biological chemistry,
Recently, we reported the synthesis of anionic lanthanide
amides (2,6-iPr2PhNH)5LnLi2(THF)2 (Ln = Sm, Nd, Y)
stabilized by simple anilido ligands, which are efficient and easily
available precatalysts for hydrophosphonylation reactions. 0.1
mol % of (2,6-iPr2PhNH)5SmLi2(THF)2 catalyzed a quantitative
transformation of a range of both aldehydes and ketones.9 Since
these complexes can be considered as additives of
(2,6-iPr2PhNH)3Ln and two equivalents of (2,6-iPr2PhNH)Li,
we were prompted to explore the role of organic alkali metal
compounds in hydrophosphonylation reactions. Alkali metal
compounds have been reported to promote the addition of
phosphorus derivatives on carbonyl compounds.10 Although
organolithium compounds are commonly used as stoichiometric
bases in organic synthesis, their application as catalysts has been
less explored.11 It turned out that a series of organolithium
compounds are highly efficient precatalysts for hydrophospho-
nylation reactions of aldehydes and ketones under mild
conditions.
The reaction of benzaldehyde with diethyl phosphite was
chosen as a model reaction to optimize reaction conditions, and
(2,6-iPr2PhNH)Li (0.2 mol %) was selected as the precatalyst,
which is equivalent to 0.1 mol % of the aforementioned complex
of (2,6-iPr2PhNH)5LnLi2(THF)2 in terms of lithium.9 The
reaction proceeded smoothly at rt in neat, and a quantitative yield
was achieved within 5 min (Table 1, entry 1). A complete
transformation of benzaldehyde to α-hydroxy phosphonate 3a
was also realized even when the amount of (2,6-iPr2PhNH)Li
was decreased to 0.1 mol % (Table 1, entry 2). However, the
yield dropped significantly when the catalyst loading was further
decreased to 0.05 mol % (Table 1, entry 3), which may be
attributed to the extremely sensitive character of
(2,6-iPr2PhNH)Li to a small amount of moisture and impurities
in the reaction mixture. A number of organolithium compounds,
S
the corresponding C−P bond formation is fundamentally
important in organic synthesis. α-Hydroxy phosphonates, one
important type of organic phosphoric compounds, possess
intriguing biological activities and have gained widespread
applications in many areas, including biological and pharma-
ceutical industries, due to their physical and structural similarity
to biologically important phosphate esters.1 Thus, the synthesis
of α-hydroxy phosphonates has received increasing attention.
Despite the numerous methods developed, the most atom-
economic and straightforward method is the Pudovic reaction,2
i.e., the nucleophilic addition of carbonyl compounds with
phosphites (also known as hydrophosphonylation reaction).
Both racemic2 and asymmetric3 α-hydroxy phosphonates are
accessible through this strategy. Generally, inorganic and organic
bases are popular promoters or catalysts for the Pudovic
reaction.4 However, most of these reactions require stoichio-
metric or even more bases,4a−d,f,g,i high temperatures of 60−70
°C4d or microwave irradiation,4f,i and reaction times of several
hours4a,b,d,g in order to obtain decent yields. Moreover, these
strategies are largely limited to a narrow scope of substances.
They mainly gave satisfactory yields for aldehydes with low yields
for ketones.4a−c,f,i Some acidic compounds, such as TFA/TfOH,5
In/HCl,6 and Ti(OiPr)4,7 reportedly mediate the hydro-
phosphonylation reactions of both aldehydes and ketones to
give moderate to high yields with high catalyst loadings and long
reaction times. In recent years, significant progress has been
achieved in this area. Some organolanthanide complexes
reportedly catalyze hydrophosphonylation reactions of alde-
hydes and ketones with high efficiency at rt under mild
conditions (in general 0.1 mol % of catalyst loading and 5−20
min of reaction time).8 However, in most cases, the synthesis of
ligands and corresponding organolanthanide complexes is
somewhat tedious and requires multiple steps. Therefore, the
development of a highly efficient and easily available catalytic
system to synthesize α-hydroxy phosphonate is still meaningful.
Received: October 21, 2014
© XXXX American Chemical Society
A
dx.doi.org/10.1021/ol5030713 | Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
aldehydes bearing a substituent at the para- or meta-position of
either an electron-donating group, such as CH3− (1c) and
CH3O− (1e, 1f), or an electron-withdrawing group, such as F−
(1g), Cl− (1i, 1j), Br− (1k), and NO2− (1l, 1m). Different from
reactions catalyzed by organolanthanide complexes,9 the steric
effect in this study is not significant. The reactions proceeded
smoothly for aldehydes with CH3− and Cl− substituents at the
ortho-position (1b and 1h). However, the catalytic system seems
to be more sensitive to the presence of the O atom at the ortho-
position, and the yield of 3d decreased slightly to 90% for p-
methoxybenzaldehyde. Coordination of the OMe group to Li
may be responsible for the reduced activity. The reaction with
furfural aldehyde is also affected by the O atom in the heterocycle
and afforded 3o in the same yield of 90%. Reaction with 1-
naphthaldehyde yielded 3n in a quantitative yield. Furthermore,
both linear and branched aliphatic aldehydes were also
expediently converted to the corresponding α-hydroxy phos-
phonates 3p−3r in 91−97% yields.
Table 1. Hydrophosphonylation of Benzaldehyde Catalyzed
by Organolithium Compounds
a
b
entry
cat. (mol %)
yield (%)
TOF (h−1
)
1
2
3
4
5
6
7
8
2,6-iPr2PhNHLi (0.2)
2,6-iPr2PhNHLi (0.1)
2,6-iPr2PhNHLi (0.05)
2,6-Me2PhNHLi (0.1)
PhNHLi (0.1)
>99
>99
86
5940
11 880
20 640
11 880
11 880
11 880
10 440
11 880
>99
>99
>99
87
(Me3Si)2NLi (0.1)
iPr2NLi (0.1)
n-BuLi (0.1)
>99
a
Reaction conditions: benzaldehyde 1a (5.0 mmol), diethyl phosphite
b
2a (6.0 mmol), catalyst (required amount), rt, 5 min. Isolated yields.
Besides diethyl phosphite, hydrophosphonylation reactions of
benzaldehyde with different phosphites were also studied (Figure
1). The reaction with diisopropyl phosphite gave rise to the
expected product 3s in 99% yield, while that with diphenyl
phosphite afforded 3t in a lower yield of 50%.
Since the performance of n-BuLi is quite promising in
catalyzing hydrophosphonylation reactions, the study was
further extended to more challenging unactivated ketones. A
range of organic alkali metal compounds were tested in the
hydrophosphonylation reaction of acetophenone with diethyl
phosphite, and in general moderate to good isolated yields were
obtained in the presence of 0.1 mol % precatalyst (Table S1,
Supporting Information).
including 2,6-Me2PhNHLi, PhNHLi, (Me3Si)2NLi, and n-BuLi,
also efficiently catalyzed this transformation and yielded 3a in
quantitative yields under mild conditions, with the exception of
lithium diisopropylamide (LDA) which led to a lower yield of
87% (Table 1, entries 4−8). Due to its easy availability, n-BuLi
was selected as the precatalyst for further study.
As shown in Figure 1, this catalytic system is applicable to
reactions of a variety of aldehydes with diethyl phosphite, and
good to excellent isolated yields of 90−99% were achieved under
optimized reaction conditions. The electronic properties of
aromatic aldehydes do not obviously influence the reaction
outcomes. Quantitative yields were obtained for aromatic
Lithium amides bearing either aromatic or aliphatic N-
substituent were studied, and the corresponding α-hydroxy
phosphonate 5a was isolated in yields of 56−78% (Table S1,
entries 1−7). Different alkali metals did not affect the catalytic
activity, and 5a was isolated in similar yields using lithium amide,
sodium amide, or potassium amide as the precatalyst (Table S1,
entries 1, 8, and 9). n-BuLi proved to be one of the best
performers by yielding 5a in 75% yield (Table S1, entry 10). The
yield of 5a dropped dramatically to 28% when the catalyst
loading decreased to 0.05 mol % (Table S1, entry 11), which is
consistent with the finding with benzaldehyde (vide supra). Due
to the ease of availability and low cost of n-BuLi, it was employed
as the precatalyst to further optimize the reaction conditions.
Attempts to improve the yield by increasing the amount of n-
BuLi failed. In fact, the isolated yield of 5a decreased from 75% to
21% as the amount of n-BuLi increased from 0.1 to 10 mol %
(Table 2, entries 1−5). This finding suggests that α-hydroxy
phosphonate probably decomposed in the presence of n-BuLi,
which is consistent with previous reports on other bases that
catalyzed/promoted the retro-hydrophosphonylation reaction.12
Thus, the reversed reaction was investigated in detail by treating
5a with n-BuLi in hexane, and the results are summarized in
Table 2 (entries 6−10). It is clear that the retro-hydrophos-
phonylation reaction did occur in the presence of n-BuLi, and the
isolated yield of acetophenone increased significantly from 3% to
75% as the loading of n-BuLi increased from 0.1 to 10 mol %.
Apparently, the amount of base plays a crucial role in the retro-
hydrophosphonylation reaction. A relatively low base loading is
preferred for the hydrophosphonylation reaction, and a high base
loading is advantageous for the retro-hydrophosphonylation
reaction. In sharp contrast, no retro-hydrophosphonylation
Figure 1. Scope of hydrophosphonylation of aldehydes catalyzed by n-
a
BuLi.a Reaction conditions: aldehyde (5.0 mmol), phosphite (6.0
mmol), n-BuLi (0.1 mol %), rt, 5 min. b Isolated yields. c h−1. d n-BuLi
(0.5 mol %), 2 h.
B
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Organic Letters
Letter
Table 2. Hydrophosphonylation and Retro-
hydrophosphonylation Reactions Catalyzed by n-BuLi
yield (%)
a
b
entry catalyst loading (mol %) time (min) temp (°C) 5a
4a
1
0.1
0.5
1.0
5.0
20
20
20
20
20
20
20
20
20
20
5
25
25
75
2
59
38
31
21
3
25
4
25
5
10
25
6
0.1
0.5
1.0
5.0
25
3
7
25
8
10
25
75
8
25
9
25
10
11
12
13
14
15
16
10
25
0.1
0.1
0.1
0.1
0.1
0.1
−25
−10
0
77
88
96
95
63
47
5
5
5
10
5
50
5
75
a
Reaction conditions: acetophenone 4a (5.0 mmol), diethyl phosphite
b
2a (6.0 mmol), n-BuLi (required amount). Isolated yields. Reaction
conditions: α-hydroxy phosphonates 5a (5.0 mmol), n-BuLi (required
amount), n-hexane (2 mL). Isolated yields.
Figure 2. Scope of hydrophosphonylation of ketones catalyzed by n-
BuLia a Reaction conditions: ketone (5.0 mmol), phosphite (6.0 mmol),
n-BuLi (0.1 mol %), 10 °C, 5 min. b Isolated yields. c h−1. d n-BuLi (0.5
mol %), 2 h, rt. e Diethyl phosphite (12.0 mmol). f Room temperature.
reaction of tertiary α-hydroxy phosphonates occurred under
identical conditions.
A further study revealed that the reversible reaction of
acetophenone with diethyl phosphite reached equilibrium within
5 min at 25 °C with 0.1 mol % n-BuLi. The yield of 5a remained
almost unchanged even after the reaction time was prolonged to
120 min (Table S2, entries 1−5, Supporting Information).
Besides the catalyst loading, the reaction temperature also plays
an important role in influencing the equilibrium of this reversible
reaction. An initial increase in the yield, followed by a decrease,
was observed when the reaction temperature increased from −25
to 75 °C (Table 2, entries 11−16). The highest yield of 96% was
observed at 0 °C (Table 2, entry 13), and a similar yield of 95%
was obtained at 10 °C (Table 2, entry 14). However, the yield
dropped significantly when the reaction temperature decreased
to lower than 0 °C, and the yield of 5a was only 77% within 5 min
at −25 °C (Table 2, entries 11 and 12), which can be attributed
to the low reaction rate at low temperatures. Meanwhile, the yield
decreased significantly from 77% to 47% when the reaction
temperature increased from 25 to 75 °C (Table 2, entries 11, 15,
and 16). These results reveal that a relatively low reaction
temperature is advantageous for the hydrophosphonylation of
acetophenone, whereas a higher reaction temperature is
preferred for the retro-hydrophosphonylation reaction, which
can be attributed to the fact that the hydrophosphonylation
reaction is exothermic, and the retro-hydrophosphonylation
reaction is endothermic. Thus, the optimal reaction conditions
for ketones are set as follows: 0.1 mol % of n-BuLi as the
precatalyst, at 10 °C, 5 min reaction time, solvent-free.
In general, n-BuLi efficiently catalyzed the hydrophosphonyla-
tion reaction of both aromatic and aliphatic ketones to give
quaternary α-hydroxy phosphonates in moderate to excellent
yields. The steric effect of ketones is profound, which is different
from that of aldehydes (vide supra). Aromatic ketones bearing an
ortho-substitution (CH3−, Cl−, Br−) on the phenyl ring showed
relatively low activity, which afforded the targeted products 5b,
5c, and 5d in yields of 35%, 79%, and 59%, respectively. In
comparison with known systems, n-BuLi still showed higher
activity for ortho-substituted ketones. For example, 4c was
converted to 5c in 52% yield within 2 h catalyzed by
(2,6-iPr2PhNH)5SmLi2(THF)2.9 On the other hand, the
electronic effect of ketones on the hydrophosphonylation
reaction is also obvious. Ketones bearing electron-withdrawing
substituents at either meta- or para-positions, including O2N−,
Br−, and F−, gave the desired products 5e−5h in nearly
quantitative yields, respectively. However, the para- substituted
substrates bearing electron-donating substituents, such as CH3−
and CH3O−, yielded the products 5i and 5j in obviously lower
yields of 84% and 72%, respectively. Reaction of 2-acetonaph-
thone yielded 5k in a quantitative yield. Ketones bearing
heterocyclic substituents such as 3-acetylpyridine and 2-
acetylthiophene were converted to the corresponding α-hydroxy
phosphonates 5l and 5m in 96% and 69% yield, respectively.
In addition to methyl ketones, other aryl and aliphatic ketones
were also tested in this transformation. The reaction with bulky
benzophenone proceeded smoothly and yielded 5n in 97% yield.
Under the optimized conditions, the reactions of various
unactivated ketones with diethyl phosphite were examined, and
the results are presented in Figure 2.
C
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Organic Letters
Letter
Tetrahedron Lett. 1990, 31, 5591. (c) Stowasser, B.; Budt, K. H.; Li, J. Q.;
Peyman, A.; Ruppert, D. Tetrahedron Lett. 1992, 33, 6625.
(2) Pudovik, A. N.; Arbuzov, B. A. Dokl. Akad. Nauk S.S.S.R. 1950, 73,
327.
2,2,2-Trifluoroacetophenone reacted with diethyl phosphite and
gave rise to fluorine-containing phosphonate 5o in 90% yield,
which is a precursor to a serine esterase inhibitor.13 Dodecano-
phenone was transformed to the expected product 5p in a
moderate yield of 40%. The reaction with benzil led to the
isolation of 5q in 55% yield, with the addition occurring to one
carbonyl group, despite the presence of 2.4 equiv of phosphite.
1,4-Addition instead of 1,2-addition occurred selectively to
chalcone, which yielded the product 5r in 86% yield. Xu et al.
reported that the reaction catalyzed by a lanthanide−lithium
complex formed 2-oxido-1,2-oxaphospholane after a sequential
phospha-Michael/Pudovik reaction, which was not detected in
this case.8h
It should be noted that, for isatin with the carbonyl group
incorporated in the heterocyclic ring, n-BuLi proved to be a
suitable precatalyst to produce α-hydroxy phosphonate 5s in
93% yield. Furthermore, linear and cyclic aliphatic ketones were
also applicable to this system, and the corresponding products
5t−5v were isolated in excellent yields of 92−96%.
The hydrophosphonylation reactions of different phosphites
with acetophenone were also studied. Diisopropyl phosphite
reacted straightforwardly and gave rise to 5w in 85% yield.
However, n-BuLi proved to be limited in catalyzing the reaction
of diphenyl phosphite and only led to a trace amount yield.
In conclusion, an easily available and inexpensive organo-
metallic compound n-BuLi was found to be a highly efficient
single-component catalyst for the hydrophosphonylation re-
action of aldehydes and unactivated ketones. Under mild
conditions, this strategy gives α-hydroxy phosphonates in
generally good to excellent yields. Moreover, n-BuLi is capable
of catalyzing both directions of the reversible Pudovik reaction of
ketones, and the amount of n-BuLi as well as reaction
temperature play crucial roles in the reaction equilibrium.
Furthermore, this system features wide substrate scopes and mild
reaction conditions (e.g., low catalyst loading, short reaction
time), which makes it the simplest and most efficient strategy for
α-hydroxy phosphonate synthesis. Study is ongoing in our
laboratory to extend this system to other transformations.
́ ́
(3) Recent reviews and papers, see: (a) Merino, P.; Marque-Lopez, E.;
Herrera, R. P. Adv. Synth. Catal. 2008, 350, 1195 and references therein.
(b) Gou, S.; Zhou, X.; Wang, J.; Liu, X.; Feng, X. Tetrahedron 2008, 64,
2864. (c) Zhao, D.; Yuan, Y.; Chan, A. S. C.; Wang, R. Chem.Eur. J.
2009, 18, 2738. (d) Boobalan, R.; Chen, C. Adv. Synth. Catal. 2013, 355,
3443. (e) Hatano, M.; Horibe, T.; Ishihara, K. Angew. Chem., Int. Ed.
2013, 52, 4549. (f) Sun, L.; Guo, Q.-P.; Li, X.; Zhang, L.; Li, Y.-Y.; Da,
C.-S. Asian J. Org. Chem. 2013, 2, 1031. (g) Deng, T.; Wang, H.; Cai, C.
Org. Biomol. Chem. 2014, 12, 5843. (h) Alegre-Requena, J. V.; Marque-
Lopez, E.; Miguel, P. J. S.; Herrera, R. P. Org. Biomol. Chem. 2014, 12,
1258.
́
́
(4) (a) Dolle, R. E.; Herpin, T. F.; Shimshock, Y. C. Tetrahedron Lett.
2001, 42, 1855. (b) Blazis, V. J.; Koeller, K. L.; Spilling, C. D. J. Org.
Chem. 1995, 60, 931. (c) Pam
68, 4815. (d) Keglevich, G.; Sipos, M.; Takac
Chem. 2007, 18, 226. (e) Rulev, A. Y. Heteroat. Chem. 2013, 24, 187.
(f) Keglevich, G.; Toth, V. R.; Drahos, L. Heteroat. Chem. 2011, 22, 15.
(g) Martínez-Castro, E.; Lop
̀
ies, O.; Backvall, J.-E. J. Org. Chem. 2003,
̈
́
s, D.; Greiner, I. Heteroat.
́
́
́ ́
ez, O.; Maya, I.; Fernandez-Bolanos, J. G.;
̃
Petrini, M. Green Chem. 2010, 12, 1171. (h) Hatano, M.; Suzuki, S.;
Takagi, E.; Ishihara, K. Tetrahedron Lett. 2009, 50, 3171. (i) Kaboudin,
B.; Nazari, R. J. Chem. Res. 2002, 291. (j) Simoni, D.; Invidiata, F. P.;
Manferdini, M.; Lampronti, I.; Rondanin, R.; Roberti, M.; Pollini, G. P.
Tetrahedron Lett. 1998, 39, 7615. (k) Simoni, D.; Rondanin, R.; Morini,
M.; Baruchello, R.; Invidiata, F. P. Tetrahedron Lett. 2000, 41, 1607.
(5) Nifant’ev, E. E.; Kukhareva, T. S.; Popkova, T. N.; Davydocchkina,
O. V. Zh. Obshch. Khim 1986, 56, 304.
(6) Das, B.; Satyalakshmi, G.; Suneel, K.; Damodar, K. J. Org. Chem.
2009, 74, 8400.
(7) Zhou, X.; Liu, Y.; Chang, L.; Zhao, J.; Shang, D.; Liu, X.; Lin, L.;
Feng, X. Adv. Synth. Catal. 2009, 351, 2567.
(8) (a) Wu, Q.; Zhou, J.; Yao, Z.; Xu, F.; Shen, Q. J. Org. Chem. 2010,
75, 8498. (b) Zhou, S.; Wang, H.; Ping, J.; Wang, S.; Zhang, L.; Zhu, X.;
Wei, Y.; Wang, F.; Feng, Z.; Gu, X.; Yang, S.; Miao, H. Organometallics
2012, 31, 1696. (c) Zhou, S.; Wu, Z.; Rong, J.; Wang, S.; Yang, G.; Zhu,
X.; Zhang, L. Chem.Eur. J. 2012, 18, 2653. (d) Zhu, X.; Wang, S.;
Zhou, S.; Wei, Y.; Zhang, L.; Wang, F.; Feng, Z.; Guo, L.; Mu, X. Inorg.
Chem. 2012, 51, 7134. (e) Miao, H.; Zhou, S.; Wang, S.; Zhang, L.; Wei,
Y.; Yang, S.; Wang, F.; Chen, Z.; Chen, Y.; Yuan, Q. Sci. China Chem.
2013, 56, 329. (f) Yang, S.; Zhu, X.; Zhou, S.; Wang, S.; Feng, Z.; Wei,
Y.; Miao, H.; Guo, L.; Wang, F.; Zhang, G.; Gu, X.; Mu, X. Dalton Trans.
2014, 43, 2521. (g) Wang, F.; Wang, S.; Zhu, X.; Zhou, S.; Miao, H.; Gu,
X.; Wei, Y.; Yuan, Q. Organometallics 2013, 32, 3920. (h) Zhang, A.; Cai,
L.; Yao, Z.; Xu, F.; Shen, Q. Heteroat. Chem. 2013, 24, 345.
(9) Liu, C.; Qian, Q.; Nie, K.; Wang, Y.; Shen, Q.; Yuan, D.; Yao, Y.
Dalton Trans. 2014, 43, 8355.
ASSOCIATED CONTENT
* Supporting Information
■
S
General procedure; Tables S1, S2; and characterizations of α-
hydroxyphosphonates. These materials are available free of
charge via the Internet at http://pubs.acs.org.
(10) (a) Consiglio, G. B.; Queval, P.; Harrison-Marchand, A.; Mordini,
AUTHOR INFORMATION
Corresponding Authors
́
A.; Lohier, J.-F.; Delacroix, O.; Gaumont, A.-C.; Gerard, H.; Maddaluno,
J.; Oulyadi, H. J. Am. Chem. Soc. 2011, 133, 6472. (b) Delacroix, O.;
Gaumont, A.-C. Curr. Org. Chem. 2005, 9, 1851.
(11) (a) Xu, L.; Wang, Y.-C.; Ma, W.; Zhang, W.-X.; Xi, Z. J. Org. Chem.
2014, DOI: 10.1021/jo501865b. (b) Zhang, W.-X.; Nishiura, M.; Hou,
Z. Chem. Commun. 2006, 3812. (c) Ong, T.-G.; O’Brien, J. S.; Korobkov,
I.; Richeson, D. S. Organometallics 2006, 25, 4728. (d) Xi, Z. Acc. Chem.
Res. 2010, 43, 1342.
■
*E-mail: yuandan@suda.edu.cn.
*E-mail: yaoym@suda.edu.cn.
Notes
The authors declare no competing financial interest.
(12) (a) Gancarz, R.; Gancarz, I.; Walkowiak, U. Phosphorus, Sulfur,
and Silicon 1995, 104, 45. (b) Sekine, M.; Nakajima, M.; Kume, A.;
Hashizume, A.; Hata, T. Bull. Chem. Soc. Jpn. 1982, 55, 224.
(13) Makhaeva, G. F.; Aksinenko, A. Y.; Sokolov, V. B.; Serebryakova,
O. G.; Richardson, R. J. Bioorg. Med. Chem. Lett. 2009, 19, 5528.
ACKNOWLEDGMENTS
■
Financial support from the National Natural Science Foundation
of China (Grant Nos. 21174095, 21132002, 21372172, and
21402135), the Major Research Project of the Natural Science of
the Jiangsu Higher Education Institutions (14KJA150007),
PAPD, and the Qing Lan Project is gratefully acknowledged.
REFERENCES
■
(1) (a) Patel, D. V.; Rielly-Gauvin, K.; Ryono, D. E. Tetrahedron Lett.
1990, 31, 5587. (b) Patel, D. V.; Rielly-Gauvin, K.; Ryono, D. E.
D
dx.doi.org/10.1021/ol5030713 | Org. Lett. XXXX, XXX, XXX−XXX