Asymmetric ring-opening reaction of oxabicyclic alkenes with aryl boronic acids catalyzed by P-containing palladacycles

Article abstract of DOI:10.1021/ol801294b

(Chemical Equation Presented) The chiral phosphine-containing palladacycle, synthesized easily from H-MOP, showed its high catalytic activity as well as asymmetric induction ability in ring-opening reaction of oxabicyclic alkenes with arylboronic acids, p

Full text of DOI:10.1021/ol801294b

ORGANIC
LETTERS
2008
Vol. 10, No. 17
3689-3692
Asymmetric Ring-Opening Reaction of
Oxabicyclic Alkenes with Aryl Boronic
Acids Catalyzed by P-Containing
Palladacycles
Ting-Ke Zhang,‡ Dong-Liang Mo,† Li-Xin Dai,† and Xue-Long Hou*,†,‡
State Key Laboratory of Organometallic Chemistry, and Shanghai-Hong Kong Joint
Laboratory in Chemical Synthesis, Shanghai Institute of Organic Chemistry,
Chinese Academy of Sciences, 354 Feng Lin Road, Shanghai 200032, China
xlhou@mail.sioc.ac.cn
Received June 9, 2008
ABSTRACT
The chiral phosphine-containing palladacycle, synthesized easily from H-MOP, showed its high catalytic activity as well as asymmetric induction
ability in ring-opening reaction of oxabicyclic alkenes with arylboronic acids, providing corresponding products in high yields and high ee.
Palladacycles represent an important class of catalyst in
organic synthesis because of their easy availability, extra
stability toward air and moisture, versatile frameworks, and
high catalytic activity.1 Since Herrmann and Beller reported
the first example using the highly active cyclopalladated tri-
o-tolylphosphine as a catalyst in Heck reaction,2 many kinds
of palladacycles have been synthesized and applied in a
variety of reactions and a high turnover number (TON) was
achieved in some reactions.3 Although palladacycles have
shown many advantages in catalysis, they are mainly used
in Heck-type reactions and coupling reactions,1,2,4,5 and
mechanistic studies showed that they served as catalyst
precursors in these kinds of reactions.1d,4m,5e,6 Asymmetric
induction has been realized in some examples;7 however,
chiral palladacycles served as Lewis acids in most cases.
Also, racemic products were given in some other examples
despite chiral palladacycles being used.5f,8 To explore the
applications of palladacycles as real transition metal catalysts
in asymmetric catalysis is still a challenge.
† State Key Laboratory of Organometallic Chemistry.
‡ Shanghai-Hong Kong Joint Laboratory in Chemical Synthesis.
(1) For some reviews: (a) Herrmann, W. A.; Bo¨hm, V. P. W.; Reisinger,
C. P. J. Organomet. Chem. 1999, 576, 23. (b) Bedford, R. B. Chem.
Commun. 2003, 1787. (c) van der Boom, M. E.; Milstein, D. Chem. ReV.
2003, 103, 1759. (d) Farina, V. AdV. Synth. Catal. 2004, 346, 1553. (e)
Beletskaya, I. P.; Cheprakov, A. V. J. Organomet. Chem. 2004, 689, 4055.
(f) Dupont, J.; Consorti, C. S.; Spencer, J. Chem. ReV. 2005, 105, 2527.
In our previous work,8,9 we developed several benzylic
substituted palladacycles and demonstrated their highly
¨
(2) Herrmann, W. A.; Brossmer, C.; Ofele, K.; Reisinger, C. P.;
Priermeier, T.; Beller, M.; Fischer, H. Angew. Chem., Int. Ed. Engl. 1995,
34, 1844.
(3) Brunel, J. M.; Heumann, A.; Buono, G. Angew. Chem., Int. Ed. 2000,
39, 1946.
10.1021/ol801294b CCC: $40.75
Published on Web 08/07/2008
2008 American Chemical Society

catalytic activity in the hydrophenylation of norbornenes and
in the ring-opening reaction of oxabicyclic alkenes with
organozinc halides prepared in situ. The 31P NMR studies
of ring-opening reaction implied that the palladacycle was
the real catalyst in the reactions. However, racemic products
were separated though the palladacycle was optically active.
After testing several reagents, it was found that optically
active product was obtained when phenylboronic acid was
used as reagent, although the ee was lower. Further study
showed that the ee value greatly increased when phosphorus-
containing palladacycle was used.5g,h,10 In this letter, we
report our preliminary results in the asymmetric ring-opening
reaction of oxabicyclic alkenes with arylboronic acids
catalyzed by palladacycles.
Table 1. Optimization of Palladacycle-Catalyzed Ring Opening
of 1a with PhB(OH)2 2aa
entry
palladacycle
solvent
yield %b
ee %c
1
4
5
5
6
7
8
9
11
11
11
11
11
11
11
11
11
11
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
THF
trace
trace
92
17
45
10
95
95
86
94
86
90
80
73
96
95
95
-
-
2
3d
4
18
57e
4
5
6
7
8
57e
-
64
65
65
65
58
55
60
76
78
79
9
10
11
12
13
14
15
16
17f
MeOH
Et2O
CCl4
At the beginning of our study, we tested the palladacycles
4-9 in the ring opening of 7-oxabicycle alkene 1a with
phenyl boronic acid 2a (eq 1, Table 1). The results showed
that all N-containing palladacycles 4-8 gave product in
DMF
CH3CN
CH2Cl2
CHCl3
CHCl3
(4) Some examples of palladacycles in Heck reaction and coupling
reactions: (a) Ohff, M.; Ohff, A.; van der Boom, M. E.; Milstein, D. J. Am.
Chem. Soc. 1997, 119, 11687. (b) Shaw, B. L.; Perera, S. D.; Staley, E. A.
Chem. Commun. 1998, 1361. (c) Ohff, M.; Ohff, A.; Milstein, D. Chem.
Commun. 1999, 357. (d) Gruber, A. S.; Zim, D.; Ebeling, G.; Monteiro,
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H. Y.; Cui, X. L.; Yuan, R. J. J. Organomet. Chem. 2001, 639, 793. (f)
Alonso, D. A.; Na´jera, C.; Pacheco, M. C. AdV. Synth. Catal. 2002, 344,
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He, M. Y. J. Organomet. Chem. 2002, 651, 146. (m) Navarro, O.; Marion,
N.; Oonishi, Y.; Kelly, R. A., III; Nolan, S. P. J. Org. Chem. 2006, 71,
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2007, 63, 5529.
a Reaction conditions: 1a:PhB(OH)2:palladacycle:Cs2CO3 ) 1:1.2:0.03:0.5.
b Isolated yield. c Determined by chiral HPLC. d Run at 60 °C. e Opposite
enantiomer observed (HPLC). f Run at 0 °C.
lower yields (entries 1-2 and 4-6), though pincer complex
6 and Overman’s palladacycle 8 provided product in 57%
ee (entries 4 and 6). Pd black also appeared using pallada-
cycle dimer 4. When the reaction proceeded at 60 °C using
benzylic substituted palladacycle 5, a 92% yield of product
in 18% ee was obtained (entry 3). However, palladacycle 9
with phosphorus as the coordination atom showed its highly
catalytic activity in the reaction, providing product 3a in 95%
yield (entry 7).
(5) Some examples of palladacycles used in other reactions: (a) Braun-
stein, P.; Matt, D.; Nobel, D. J. Am. Chem. Soc. 1988, 110, 3207. (b)
Herrmann, W. A.; Bo¨hm, V. P. W.; Reisinger, C. P. J. Organomet. Chem.
1999, 576, 23. (c) Beydoun, N.; Pfeffer, M. Synthesis 1990, 729. (d) Gies,
A. E.; Pfeffer, M.; Sirlin, C.; Spencer, J. Eur. J. Org. Chem. 1999, 1957.
(e) Gai, X. J.; Grigg, R.; Ramzan, M. I.; Sridharan, V.; Collard, S.; Muir,
J. E. Chem. Commun. 2000, 2053. (f) Bravo, J.; Cativiela, C.; Navarro, R.;
Urriolabeitia, E. P. J. Organomet. Chem. 2002, 650, 157. (g) He, P.; Lu,
Y.; Dong, C.-G.; Hu, Q.-S. Org. Lett. 2007, 9, 343. (h) Bedford, R. B.;
Betham, M.; Charmant, J. P. H.; Haddow, M. F.; Orpen, A. G; Pilarski,
L. T.; Coles, S. J; Hursthouse, M. B. Organometallics 2007, 26, 6346.
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2359. (b) Brody, M. S.; Finn, M. G. Tetrahedron Lett. 1999, 40, 415.
(7) (a) Navarro, R.; Urriolabeitia, E. P.; Cativiela, C.; Diaz-de-Villegas,
M. D.; Lopez, M. P.; Alonso, E. J. Mol. Catal. A: Chem. 1996, 105, 111.
(b) Hollis, T. K.; Overman, L. E. Tetrahedron Lett. 1997, 38, 8837. (c)
Leung, P. H.; Ng, K.-H.; Li, Y. X.; White, A. J. P.; Williams, D. J. Chem.
Commun. 1999, 2435. (d) Donde, Y.; Overman, L. E. J. Am. Chem. Soc.
1999, 121, 2933. (e) Overman, L. E.; Remarchuk, T. P. J. Am. Chem. Soc.
2002, 124, 12. (f) Anderson, C. E.; Overman, L. E. J. Am. Chem. Soc.
2003, 125, 12412. (g) Moyano, A.; Rosol, M.; Moreno, R. M.; Lo´pez, C.;
Maestro, M. A. Angew. Chem., Int. Ed. 2005, 44, 1865. (h) Anderson, C. E.;
Donde, Y.; Douglas, C. J.; Overman, L. E. J. Org. Chem. 2005, 70, 648.
(i) Kirsch, S. F.; Overman, L. E. J. Am. Chem. Soc. 2005, 127, 2866. (j)
Weiss, M. E.; Fischer, D. F.; Xin, Z.-q.; Jautze, S.; Schweizer, W. B.; Peters,
R. Angew. Chem., Int. Ed. 2006, 45, 5694. (k) Jautze, S.; Seiler, P.; Peters,
R. Angew. Chem., Int. Ed. 2007, 46, 1260. (l) Fischer, D. F.; Xin, Z.-q.;
Peters, R. Angew. Chem., Int. Ed. 2007, 46, 7704. (m) Nomura, H.; Richards,
C. J. Chem.-Eur. J. 2007, 13, 10216.
The above results indicate that the catalytic activity of
P-palladacycles is higher than N-palladacycles. This sug-
gested that chiral P-palladacycles should be synthesized and
tested. H-MOP was used as starting material because it has
demonstrated its excellent asymmetric induction ability in
many reactions.11 Reaction of (S)-H-MOP and Pd(OAc)2 in
the ratio 1:1 in toluene at 50 °C led to the formation of the
axial-chiral palladacycle 11 in 65% yield, which is air,
(8) (a) Yuan, K.; Zhang, T.-K.; Hou, X.-L. J. Org. Chem. 2005, 70,
6085. (b) Zhang, T.-K.; Yuan, K.; Hou, X.-L. J. Organomet. Chem. 2007,
692, 1912.
(9) Zhang, T.-K.; Mo, D.-L.; Hou, X.-L.; Dai, L.-X. The paper is under
review.
¨
(10) (a) For review: Herrmann, W. A.; Ofele, K.; von Preysing, D.;
Schneider, S. K. J. Organomet. Chem. 2003, 687, 229. (b) Tenaglia, A.;
Giordano, L.; Buono, G. Org. Lett. 2006, 8, 4315
.
3690
Org. Lett., Vol. 10, No. 17, 2008

moisture, and thermally stable. It was converted to P-
palladacycle 13 by treatment with proline sodium salt
(Scheme 1). The structure of 13 was confirmed by X-ray
diffraction analysis (see Supporting Information), from which
we can see that Pd connects with C2′ of H-MOP.12
Scheme 1. Synthesis of P-Containing Palladacycles 11 and 13
With chiral P-containing palladacycle 11 in hand, it was
applied in the ring-opening reaction of oxabicycles with aryl
boronic acids. The results are listed in Table 1.
From Table 1, we can see that the reaction proceeded
smoothly in most solvents to give the product in excellent
yields (entries 8-17). The best result was obtained when
chloroform was used as solvent, when the ee value of the
product 3a was 78% and the yield was 95% (entry 16). The
ee value for 3a was 79% when the reaction was run at 0 °C
(entry 17). When other bases, such as potassium fluoride,
potassium orthophosphate, and potassium carbonate were
Table 2. Asymmetric Ring Opening of Oxabicyclic Alkenes with Aryl Boronic Acidsa
a Reaction conditions: 1:2:11:Cs2CO3 ) 1:1.2:0.03:0.5. b Isolated yield. c Determined by chiral HPLC.
Org. Lett., Vol. 10, No. 17, 2008
3691

used, almost the same yields of product but lower ee values
were obtained (not shown in the table).
In conclusion, a highly efficient ring-opening reaction has
been realized using chiral palladacycle as the catalyst, which
represents an example of a palladacycle as a transition metal
catalyst in asymmetric catalysis. Further investigations on
the applications of palladacycles in asymmetric reactions are
in progress.
Under the optimized conditions, the substrate scope of the
oxabicyclic alkenes and aryl boronic acids was evaluated
(eq 2, Table 2). Phenylboronic acid (entries 1 and 9-11)
and most of the aryl boronic acids with electon-donating
groups (entries 2, 5, and 12) and electron-withdrawing groups
(entries 3, 4, 6, and 13) reacted with different substituted
oxabicyclic alkenes 1 smoothly to provide corresponding
ring-opening products in good to excellent yields. The ee
values were from 68% to 83%, except for 2-methylphenyl
and naphthylboronic acids, which gave products in good yield
but lower ee (entry 7 and entry 8). Substituents on the
oxabicyclic alkene have some effect on the reaction. For
example, the ee value of the product increased to 83% when
an electron-withdrawing group Br was present in 1 (entry
10), while the presence of electron-donating Me and MeO
groups in 1 lowered the ee value of the products (entry 9
and entry 11). The substituents did not, however, influence
the yields. Cinnamyl boronic acid was also a suitable reagent
for the reaction, providing the product in 76% yield and in
79% ee (entry 14). The absolute configuration of product
3a was assigned as (1R, 2S) by comparison its HPLC trace
with that of an authentic sample.13
Acknowledgment. Financially supported by the Major
Basic Research Development Program (2006CB806100),
National Natural Sciences Foundation of China (20532050,
20672130), Chinese Academy of Science, Croucher
Foundation of Hong Kong, and Shanghai Committee of
Science and Technology. T.K.Z. gratefully thanks the
Croucher Foundation of Hong Kong for a studentship. This
paper is dedicated to Professor Xiyan Lu on the occasion
of his 80th birthday.
Supporting Information Available: Synthesis of palla-
dacycles 11 and 13 and CIF file for 13. Experimental procedure
for ring opening-reaction, 1H and 13C NMR spectra, as well as
HPLC data for products 3. This material is available free of
charge via the Internet at http://pubs.acs.org.
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