LETTER
Efficient Ligand for the Mizoroki–Heck Reaction
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range of functional groups. As expected, the reaction of
iodobenzene, 4-iodotoluene, 1-iodo-4-methoxybenzene,
1-iodonaphthalene, and 2-iodothiophene all proceeded
very smoothly within 0.25 to 2 hours to give the desired
products in 80–97% isolated yield (Table 2, entries 1–5,
7–10). However, the reaction of sterically hindered 2-io-
dotoluene with styrene gave a lower yield (entry 6). Under
these same reaction conditions, coupling of bromoben-
zene with styrene gave a very poor yield (16%) after 48
hours (entry 11); therefore, tetrabutylammonium bromide
(1 equiv) was added to the reaction mixture for the cross-
coupling of aryl bromides or chlorides with alkenes. Acti-
vated aryl bromides, such as 1-bromo-4-nitrobenzene, 4-
bromobenzonitrile, and 4-bromobenzaldehyde, then cou-
pled rapidly in high yields (entries 14, 15, 18, and 19).
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Principles and Applications of Organotransition Metal
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We also investigated the Mizoroki–Heck cross-coupling
of styrene with activated aryl chlorides, such as 4-chloro-
acetophenone and 4-chlorobenzonitrile, as well as nonac-
tivated electron-neutral chlorobenzene under similar
reaction conditions in the presence of tetrabutylammoni-
um bromide (1 equiv) (entries 20–22). Compared with the
corresponding bromo analogues, the reactions of the chlo-
ro derivatives gave moderate yields and required longer
times.
In summary, the palladium chloride–cryptand 22 complex
has been introduced as a potential catalyst for Mizoroki–
Heck reactions of aryl halides with terminal olefins under
phosphine-free conditions. This catalyst has the advantag-
es of being thermally stable, readily synthesized, inexpen-
sive, easily handled, and operating under air.
Furthermore, cryptand-22 might act as a ligand in stabiliz-
ing the palladium(0) species in the Mizoroki–Heck reac-
tion.
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Tetrahedron 2008, 64, 4268.
(15) Aralkenes 3; General Procedure
A 5 mL round-bottomed flask was charged with aryl halide
1 (1 mmol), alkene 2 (1.1 mmol), PdCl2–cryptand 22 (0.009
mmol, 0.9 mol%), Et3N (1.1 mmol), and DMF (1 mL). [For
aryl bromides or chlorides, TBAB (1 mmol) was also
added]. The mixture was stirred at 130 °C for the appropriate
time (Table 2) while the progress of the reaction was
monitored (TLC). Upon completion of the reaction, the
mixture was cooled to r.t., poured into H2O (10 mL), and
extracted with CH2Cl2 (3 × 8 mL). The combined organic
extracts were washed with brine (2 × 8 mL), dried (MgSO4),
and concentrated. Purification by preparative TLC [silica
gel, hexane or hexane–EtOAc (9:1)] gave the pure product.
1-Methyl-4-[(E)-2-phenylvinyl]benzene (3e)
Acknowledgment
We thank the Research Council of K. N. Toosi University of Tech-
nology for financial support. The authors express their gratitude to
Dr. Sogand Noroozizadeh for editing the English content of this ma-
nuscript.
References and Notes
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1086.
White solid; yield: 175 mg (90%); mp 119–122 °C (Lit.2a
120–122 °C). 1H NMR (300 MHz, CDCl3): δ = 2.41 (s, 3 H),
7.13 (s, 2 H), 7.22 (d, J = 7.9 Hz, 2 H), 7.29 (t, J = 7.3 Hz, 1
H), 7.40 (t, J = 7.3 Hz, 2 H), 7.47 (d, J = 7.9 Hz, 2 H), 7.55
(d, J = 7.4 Hz, 2 H). 13C NMR (75 MHz, CDCl3): δ = 21.3,
126.45, 126.49, 127.5, 127.7, 128.65, 128.7, 129.5, 134.6,
137.55, 137.57.
1-Methyl-2-[(E)-2-phenylvinyl]benzene (3f)
Pale-yellow oil; yield: 138 mg (72%). 1H NMR (300 MHz,
CDCl3): δ = 2.51 (s, 3 H), 7.08 (d, J = 16.1 Hz, 1 H), 7.26–
7.47 (m, 7 H), 7.61 (d, J = 7.6 Hz, 2 H), 7.68 (d, J = 6.5 Hz,
1 H). 13C NMR (75 MHz, CDCl3): δ = 20.0, 125.4, 126.3,
126.6, 126.7, 127.65, 127.69, 128.8, 130.1, 130.5, 135.9,
136.5, 137.8.
1-Methoxy-4-[(E)-2-phenylvinyl]benzene (3g)
© Georg Thieme Verlag Stuttgart · New York
Synlett 2013, 24, A–D