V. V. Thakur et al. / Tetrahedron Letters 45 (2004) 2915–2918
2917
Table 3. Heck reaction between alkenes and aryl halides catalyzed by
palladacycle 1a
Finally, moderate yields of symmetrical biaryls were
obtained when a variety of substituted aryl iodides were
subjected to Ullmann-type coupling (Scheme 3).
No
1
Aryl halide
C6H5I
Alkene
Yield (%)b TONc
Styrene
Styrene
Styrene
BAf
20d
38e
94
97
67
68
94
88
99
97
65
99
21
80,000
In conclusion, a new family of sulfilimine palladacycles
has been shown to exhibit high activity in a variety of
C–C bond forming reactions using aryl halides (X ¼ I,
Br, Cl). The stability of these palladacycles against air,
moisture and temperature and the fact that they can
be synthesized from inexpensive and readily avail-
able starting materials render them very promising
catalysts.
153,600
392,800
396,000
269,000
136,000
376,000
528,900j
594,000j
388,000
260,000
397,200
76,000
MMAg
ANh
EAi
EA
2
3
4
4-MeOC6H4I
4-ClC6H4I
4-O2NC6H4I
EA
Styrene
BA
5
6
7
4-HOC6H4I
4-H2NC6H4I
C6H5Br
Styrene
MAk
Acknowledgements
a Conditions: aryl halide (2 mmol), olefin (2 mmol), Et3N (4 mmol),
palladacycle
1
(5 ꢁ 10ꢀ6 mmol), NMP (6 ml), substrate/cat. ¼
0.4 ꢁ 106, 140 ꢁC, 12 h.
V.V.T. and C.R.K. thank CSIR, New Delhi for the
award of Senior Research Fellowship (SRF). The au-
thors thank Dr. B. D. Kulkarni, Head, Chemical
Engineering and Process Development Division for his
constant encouragement.
b Isolated yields after chromatographic purification.
c TON ¼ mmol of product/mmol of Pd.
d K2CO3 is used as a base.
e NaOAc is used as a base.
f n-Butyl acrylate.
g Methyl methacrylate.
h Acrylonitrile.
i Ethyl acrylate.
References and notes
j Aryl halide (3 mmol), olefin (3 mmol), Et3N (6 mmol).
k Methyl acrylate.
1. (a) Tsuji, J. Palladium Reagents and Catalysts; Wiley:
Chichester, 1995; (b) Malleron, J. L.; Fiaud, J. C.; Legros,
J. Y. Handbook of Palladium-Catalysed Organic Reactions;
San Diego, 1997; (c) Transition Metals for Organic
Synthesis; Beller, M., Bolm, C., Eds.; Wiley-VCH: Wein-
heim, 1998; Vols. 1 and 2; (d) Metal Catalysed Cross
Coupling Reactions; Diederich, F., Stang, P. J., Eds.;
Wiley-VCH: Weinheim, 1998; (e) Li, J. J.; Gribble, G. W.
In Palladium in Heterocyclic Chemistry; Pergamon:
Oxford, 2000; (f) Handbook of Organopalladium Chemistry
for Organic Synthesis, Volume 2; Negishi, E.I.; de Meijere,
A., Eds.; Wiley: New York, 2002; (g) Dupont, J.; Pfeffer,
M.; Spencer, J. Eur. J. Inorg. Chem. 2001, 1917–
1927.
tions have recently been developed.18 We also evaluated
the effectiveness of palladacycle 1 for Sonogashira and
Ullmann-type coupling19 reactions (Table 4 and Scheme
3). As can be seen from Table 4, very high yields were
obtained in the Sonogashira reaction of phenylacetylene
with aryl iodides, at 80 ꢁC under copper-free conditions.
The reaction also worked well with propargyl alcohol to
afford the corresponding coupled product in 50% yield.
2. (a) Heck, R. F. Palladium Reagents in Organic Synthesis;
Academic: London, 1985; (b) Grushin, V. V.; Alper, H.
Chem. Rev. 1994, 94, 1047–1062; (c) Herrmann, W. A.;
Brossmer, C.; Ofele, K.; Reisinger, C.; Priermeier, T.;
Beller, M.; Fischer, H. Angew. Chem. Int. Ed. 1995, 34,
1844–1848; (d) Herrmann, W. A. Catalytic Carbon–
Carbon Coupling by Palladium Complexes: Heck Reac-
tions. In Applied Homogeneous Catalysis with Metal
Complexes; Collins, B., Ed.; VCH: Weinheim, 1996; (e)
Milstein, D.; Boom, M. E.; Ohff, A.; Ohff, M. J. Am.
Chem. Soc. 1997, 119, 11687–11688; (f) Alonso, D. A.;
Najera, C.; Pacheco, M. C. Org. Lett. 2000, 2, 1823–1826;
(g) Iyer, S.; Ramesh, C. Tetrahedron Lett. 2000, 41, 8981–
8984; (h) Consorti, C. S.; Zanini, M. L.; Leal, S.; Ebeling,
G.; Dupont, J. Org. Lett. 2003, 5, 983–986.
Table 4. Sonogashira coupling between aryl halides and phenylacetyl-
ene catalyzed by palladacycle 1a
No
Aryl halide
Yield (%)b
TONc
1
2
3
4
C6H5I
84
88
25
10
336
352
100
40
4-O2NC6H4I
C6H5Br
C6H5Cl
a Conditions: aryl halide (2 mmol), phenylacetylene (3 mmol), Et3N
(6 ml), palladacycle 1 (0.005 mmol), substrate/cat. ¼ 400, 80 ꢁC,12 h.
b Isolated yields after chromatographic purification.
c TON ¼ mmol of product/mmol of Pd.
3. (a) Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457–
2483; (b) Suzuki, A. J. Organomet. Chem. 1999, 576, 147–
168; (c) Kotha, S.; Lahini, K.; Kashinath, D. Tetrahedron
2002, 58, 9633–9695; (d) Pramick, M. R.; Rosemeier, S.
M.; Beranek, M. T.; Nickse, S. B.; Stone, J. J.; Stockland,
R. A., Jr.; Baldwin, S. M.; Kastner, M. E. Organometallics
2003, 22, 523–528.
4. (a) Wolfe, J. P.; Tomori, H.; Sadighi, J. P.; Yin, J.;
Buchwald, S. L. J. Org. Chem. 2000, 65, 1158–1174; (b)
Huang, X.; Anderson, K. W.; Zim, D.; Jiang, L.; Klapars,
A.; Buchwald, S. L. J. Am. Chem. Soc. 2003, 125,
(0.005 mmol)
hydroquinone (50 mol %)
cat 1
R
I
R
R
o
K2CO3, NMP, 125 C, 24 h
R = H; 41%, TON = 164
R = CN; 35%, TON = 140
R = Cl; 44%, TON = 176
;
R = NO2 48%, TON = 192
Scheme 3. Ullmann-type coupling of aryl halides.