A novel catalytic activity of bismuth(III) salts in palladium(II)-catalyzed atom economical Michael-type hydroarylation of nitroalkenes with aryltin compounds

Article abstract of DOI:10.1016/S0040-4039(01)02387-5

A novel catalytic effect of bismuth(III) salts such as BiCl₃, Bi₂O₃, and Bi(NO₃)₃·5H₂O has been disclosed in new palladium(II)-catalyzed Michael-type hydroarylation of nitroalkenes with aryltin compounds. The reaction is atom economical in the tin compounds and slightly fewer than four aryl groups of tetraaryltins can be transferred to the products.

Full text of DOI:10.1016/S0040-4039(01)02387-5

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 43 (2002) 1269–1271
A novel catalytic activity of bismuth(III) salts in
palladium(II)-catalyzed atom economical Michael-type
hydroarylation of nitroalkenes with aryltin compounds
Toshiyuki Ohe and Sakae Uemura*
Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Sakyo-ku,
Kyoto 606-8501, Japan
Received 12 November 2001; revised 13 December 2001; accepted 14 December 2001
Abstract—A novel catalytic effect of bismuth(III) salts such as BiCl3, Bi2O3, and Bi(NO3)3·5H2O has been disclosed in new
palladium(II)-catalyzed Michael-type hydroarylation of nitroalkenes with aryltin compounds. The reaction is atom economical in
the tin compounds and slightly fewer than four aryl groups of tetraaryltins can be transferred to the products. © 2002 Elsevier
Science Ltd. All rights reserved.
Recently, we have reported palladium(II)-catalyzed
atom economical Michael-type hydroarylation of a,b-
unsaturated ketones and aldehydes with aryltin
compounds1 as one of our series of studies on organic
transformations using organoheteroatom compounds
such as organoborons,2 organoantimonys,3 and
organobismuths.4 We now communicate our prelimi-
nary results of application of this reaction to nitroalke-
nes to give the corresponding hydroarylation products5
where various bismuth(III) salts work as good catalysts
for improving their yield. The catalysis of bismuth(III)
salts on a variety of organic transformations including
carbon-carbon bond forming reactions is of current
interest.6
tion product, 2-nitro-1,1-diphenylethane (3ah), and
biphenyl (4h) were obtained in 14% (0.28 mmol) and
23% (0.23 mmol) isolated yields, respectively (Eq. (1)).
The use of five times PdCl2 (0.10 mmol) resulted in the
increase of both 3ah (52% yield, 1.04 mmol) and 4h
(39% yield, 0.39 mmol) (Table 1, Entry 1). Here, the
yield of 3ah was much improved than that of 4h and
just above two phenyl moieties of 2h were transferred
to the product 3ah.
Since we have already shown that antimony(III) chlo-
ride worked quite effectively in Pd(II)-catalyzed
Michael-type hydroarylation of a,b-unsaturated
ketones and aldehydes with organoborons,2b,2c we
looked for various Lewis acidic metal salts to accom-
plish a highly atom economical transformation produc-
ing 3ah. Eventually, it was disclosed that a variety of
bismuth(III) salts such as BiCl3, Bi2O3, and Bi(NO3)3·
5H2O worked as quite effective catalysts for this
At first, b-nitrostyrene (1a, 2 mmol) was treated with
tetraphenyltin (2h, 0.5 mmol) in the presence of PdCl2
(0.02 mmol) and LiCl (4 mmol)7 in AcOH (20 mL) at
25°C for 20 h. As a result, the Michael-type hydroaryla-
cat. PdCl2
/ LiCl
R
R
+
+
Ar–Ar
Ar4Sn
NO2
NO2
AcOH
(cat. BiCl3)
25 ˚C
Ar
1
2
3
4
a: R = Ph
h: Ar = Ph
b: R = p-MeC6H4 i: Ar = p-MeC6H4
c: R = p-MeOC6H4 j: Ar = p-ClC6H4
d: R = p-ClC6H4
(1)
e: R = p-BrC6H4
f: R = m-NO2C6H4
g: R = n-C7H15
* Corresponding author.
0040-4039/02/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(01)02387-5

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T. Ohe, S. Uemura / Tetrahedron Letters 43 (2002) 1269–1271
Table 1. Pd(II)-catalyzed hydroarylation of nitroalkenes (1) using aryltin compounds (2) in the presence and absence of
Bi(III) salta
Entry
1
2
Bi(III) salt
(mmol)
Isolated yield (%)b
R
Ar
3
4
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
BiCl3
Bi2O3
Bi(NO3)3·5H2O
BiCl3
BiCl3
BiCl3
BiCl3
BiCl3
BiCl3
0.1
0.05
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
83 (52c)
85
81
16 (39c)
15
9
p-MeC6H4
p-MeOC6H4
p-ClC6H4
p-BrC6H4
m-NO2C6H4
n-C7H15
Ph
p-ClC6H4
Ph
Ph
82 (59)
81 (50)
88 (50)
85 (53)
77 (37)
78 (68)
76 (67c)
(63)
10 (31)
15 (33)
6 (43)
13 (35)
16 (36)
3 (16)
17 (19c)
(24)
p-MeC6H4
p-MeC6H4
p-ClC6H4
Ph3SnCld
BiCl3
BiCl3
BiCl3
BiCl3
0.1
0.1
0.1
13 (13c)
27 (39c)
70 (70c)
62 (71c)
37 (44c)
13 (19c)
e
Ph
Ph2SnCl2
a Reaction conditions: 1 (1 mmol), 2 (0.25 mmol), PdCl2 (0.05 mmol) and LiCl (2 mmol) in AcOH (10 mL) at 25°C for 20 h.
b The yields obtained in the absence of Bi(III) salt are shown in parentheses. Based on 2; 1 mmol as Ar group: 1 mmol of 3 and 0.5 mmol of 4
correspond to 100% yield, respectively.
c Double scale reaction.
d 0.33 mmol.
e 0.5 mmol.
transformation8,9 as in the cases of the so far known
BiCl3 catalysis in Mukaiyama-aldol and some Michael-
type reactions.10 Thus, the addition of BiCl3 (0.1 molar
amount of 1a) improved the yield of 3ah from 52% to
83% by the sacrifice of the yield of 4h from 39% to 16%
as shown in Entry 1. Similar trends were also observed
in the reactions using various nitrostyrenes having a
substituent at the aromatic ring and 1-nitro-1-nonene
(Table 1). The most atom economical reaction we
found so far is that between 1-(p-chlorophenyl)-2-
nitroethene (1d) and tetraphenyltin (2h) in the presence
of BiCl3, where 88% of hydroarylation product 3dh was
isolated, showing that 3.52 phenyl moieties of Ph4Sn
were transferred to the product 3dh. Some other phenyl
moieties were employed to produce biphenyl (6% yield,
0.24 phenyl moieties) (Entry 6). At present, this cata-
lytic reaction could not be applied to a-alkyl-substi-
tuted nitroalkenes such as 2-nitro-1-phenyl-1-propene
and 1-nitro-1-cyclohexene.
dium species as A. From the species A, a palladium
species is eliminated in the state of divalent Pd to give
a bismuth enolate B, protonolysis of which gives the
hydroarylation product. Further study to widen the
applicability of this hydroarylation including enantiose-
lective reaction11 and to clarify the reaction mechanism
is now in progress.
X
A
XPd
BiX2
O
R
R
OBiX2
N
N
O
Ar
O
Ar
A
B
References
1. Ohe, T.; Wakita, T.; Motofusa, S.-i.; Cho, C. S.; Ohe, K.;
Uemura, S. Bull. Chem. Soc. Jpn. 2000, 73, 2149–2155.
2. (a) Cho, C. S.; Itotani, K.; Uemura, S. J. Organomet.
Chem. 1993, 443, 253–259; (b) Cho, C. S.; Motofusa,
S.-i.; Uemura, S. Tetrahedron Lett. 1994, 35, 1739–1742;
(c) Cho, C. S.; Motofusa, S.-i.; Ohe, K.; Uemura, S.;
Shim, S. C. J. Org. Chem. 1995, 60, 883–888; (d) Cho, C.
S.; Uemura, S. J. Organomet. Chem. 1994, 465, 85–92; (e)
Cho, C. S.; Ohe, T.; Uemura, S. J. Organomet. Chem.
1995, 496, 221–226.
3. (a) Cho, C. S.; Tanabe, K.; Uemura, S. Tetrahedron Lett.
1994, 35, 1275–1278; (b) Cho, C. S.; Motofusa, S.-i.; Ohe,
K.; Uemura, S. Bull. Chem. Soc. Jpn. 1996, 69, 2341–
2348; (c) Cho, C. S.; Tanabe, K.; Itoh, O.; Uemura, S. J.
Org. Chem. 1995, 60, 274–275; (d) Matoba, K.; Moto-
fusa, S.-i.; Cho, C. S.; Ohe, K.; Uemura, S. J. Organomet.
Chem. 1999, 574, 3–10.
Among other aryltin compounds examined, tetrakis(p-
methylphenyl)tin (2i) and diphenyltin dichloride gave
reasonable yield of the corresponding hydroarylation
product, 3ai, 3di, and 3ah, respectively (Entries 10, 11,
and 14), but in the cases of tetrakis(p-chlorophenyl)tin
(2j) (Entry 12), triphenyltin chloride (Entry 13), and
tributylphenyltin the yield of 3 was lower even in the
presence of BiCl3. Other bismuth(III) salts such as
Bi2O3, Bi(NO3)3·5H2O were also revealed to be as effec-
tive as BiCl3 (Entries 2 and 3).
The reaction seems to proceed via transmetallation of
Sn(IV) moiety of aryltins by Pd(II) to give an
ArPd(II)X (X=Cl or OAc) species which adds to
nitroalkenes activated by coordination of Bi(III) salt to
the oxygen of nitro group to afford such an alkylpalla-

T. Ohe, S. Uemura / Tetrahedron Letters 43 (2002) 1269–1271
1271
4. (a) Cho, C. S.; Ohe, T.; Itoh, O.; Uemura, S. J. Chem.
Soc., Chem. Commun. 1992, 453–454; (b) Cho, C. S.;
Yoshimori, Y.; Uemura, S. Bull. Chem. Soc. Jpn. 1995,
68, 950–957.
6. Organobismuth Chemistry; Suzuki, H.; Matano, Y., Eds.
Elsevier: London, 2001; Chapter 5.
7. The role of LiCl is to solubilize PdCl2 and also to
coordinate to organotins making transmetallation with
Pd salt facile as reported in Ref. 1.
8. In the case of Pd(II)-catalyzed hydroarylation of a,b-
unsaturated ketones and aldehydes using organoborons,
BiCl3 showed only a low catalytic activity as reported in
Refs. 2b,c.
9. The metal salts such as BF3·Et2O, AlCl3, and InCl3 did
not show any positive catalytic effect, while SbCl3
showed a slightly less catalytic activity than BiCl3.
10. (a) Ohki, H.; Wada, M.; Akiba, K.-y. Tetrahedron Lett.
1988, 29, 4719–4722; (b) Wada, M. Yuki Gosei Kagaku
Kyokaishi (J. Synth. Org. Chem. Jpn.) 1990, 48, 960–961.
11. In the paper of Ref. 5a, a quite highly enantioselective
hydroarylation of nitroalkenes was reported. Under our
present conditions, the reaction did not proceed at all
with PhB(OH)2 in place of organotin compounds.
5. Examples of transition metal-catalyzed or -mediated
Michael-type conjugate addition to nitroalkenes using
organoheteroatom compounds: (a) Organoboronic acids-
Rh(I) (catalyzed), Hayashi, T.; Senda, T.; Ogasawara, M.
J. Am. Chem. Soc. 2000, 122, 10716–10717; (b) dialkylz-
inc-Cu(II) (catalyzed), Alexakis, A.; Benhaim, C. Org.
Lett. 2000, 2, 2579–2581; (c) Ongeri, S.; Piarulli, U.;
Jackson, R. F. W.; Gennari, C. Eur. J. Org. Chem. 2001,
803–807; (d) aryl iodide-Pd (mediated), Denmark, S. E.;
Schnute, M. E. J. Org. Chem. 1995, 60, 1013–1019.
Compared to these examples, where an excess amount of
either organoborons or dialkylzinc and also a stoichio-
metric amount of Pd salt were employed, our present
method is atom economical in organoheteroatom com-
pounds by use of a catalytic amount of Pd salt.