Palladium-catalyzed cross-coupling of organoboron compounds with iodonium salts and iodanes

Article abstract of DOI:10.1021/jo960195m

The palladium-catalyzed cross-coupling reaction of iodinanes (iodonium salts and iodanes) with organoboron compounds to form carbon-carbon bonds was achieved at ambient temperature under aqueous conditions in the absence of base. Coupling of phenylboronic acid with diphenyliodonium tetrafluoroborate in the presence of Pd(PPh₃)₄ (0.2 mol %) or Pd(OAc)₂ (0.2 mol %) under aqueous conditions gave biphenyl in almost quantitative yield. Under the same conditions, substituted boronic acids, boronates, and trialkylboranes were readily coupled with diaryl-, alkenyl-, and alkynyliodonium salts. Finally, the iodanes ArI(OH)OTs underwent cross-coupling with boronic acids, boronates, and trialkylboranes to afford biphenyls and aryl-substituted alkenes.

Full text of DOI:10.1021/jo960195m

4720
J . Org. Chem. 1996, 61, 4720-4724
P a lla d iu m -Ca ta lyzed Cr oss-Cou p lin g of Or ga n obor on Com p ou n d s
w ith Iod on iu m Sa lts a n d Iod a n es
Suk-Ku Kang,* Hong-Woo Lee, Su-Bum J ang, and Pil-Su Ho
Department of Chemistry, Sung Kyun Kwan University, Natural Science Campus, Suwon 440-746, Korea
Received J anuary 30, 1996X
The palladium-catalyzed cross-coupling reaction of iodinanes (iodonium salts and iodanes) with
organoboron compounds to form carbon-carbon bonds was achieved at ambient temperature under
aqueous conditions in the absence of base. Coupling of phenylboronic acid with diphenyliodonium
tetrafluoroborate in the presence of Pd(PPh3)4 (0.2 mol %) or Pd(OAc)2 (0.2 mol %) under aqueous
conditions gave biphenyl in almost quantitative yield. Under the same conditions, substituted
boronic acids, boronates, and trialkylboranes were readily coupled with diaryl-, alkenyl-, and
alkynyliodonium salts. Finally, the iodanes ArI(OH)OTs underwent cross-coupling with boronic
acids, boronates, and trialkylboranes to afford biphenyls and aryl-substituted alkenes.
In tr od u ction
Resu lts a n d Discu ssion
Cr oss-Cou p lin g w ith Iod on iu m Sa lts. A. Cou -
p lin g of P h en ylbor on ic Acid w ith Dip h en yliod o-
n iu m Tetr a flu or obor a te. The palladium-catalyzed
cross-coupling of arylboronic acids with aryl halides to
give unsymmetrical biaryls has been reported previ-
ously.9,10 Snieckus2c utilized aryl triflates instead of aryl
halides in Pd-catalyzed cross-coupling with arylboronic
acids to synthesize unsymmetrical biaryls. In our at-
tempts to find an alternative to halides and triflates for
mild conditions, we focused our attention on hypervalent
iodine compounds. We found that excellent yields of
unsymmetrical biaryls could be obtained under extremely
mild conditions when arylboronic acids were reacted with
hypervalent iodonium salts using 0.2 mol % Pd(PPh3)4
or ligand-free Pd(OAc)2 as a catalyst. To determine
suitable reaction conditions, a series of experiments were
performed on the coupling of phenylboronic acid with
diphenyliodonium tetrafluoroborate to form biphenyl (8a )
(eq 2). The results are summarized in Table 1.
The palladium-catalyzed cross-coupling of organobo-
ranes (boronic acids, boronates, and trialkylboranes) with
organic electrophiles (i.e., halides and triflates) in the
presence of base is known as the Suzuki reaction1 and
has become an extremely powerful tool in organic syn-
thesis. These coupling reactions tolerate many functional
groups, yield easily removable nontoxic byproducts, and
use nontoxic and readily available organoboranes. Con-
sequently, they are utilized extensively in the syn-
thesis of natural products. However, coupling with aryl
or vinyl halides and triflates usually requires a longer
reaction time at a higher temperature.1,2 These relatively
drastic conditions may reduce the yields due to the
thermal instability of the substrates, products, or the
catalyst itself. In some cases, the use of bases such as
TlOH and Ba(OH)2 allows the reaction to proceed at room
temperature in biaryl couplings.3 In connection with
our programs to utilize hypervalent iodonium salts4,5
and iodanes4,6 as electrophiles for palladium-catalyzed
C-C bond formation,7 we report here the palladium-
catalyzed cross-coupling of organoboranes8 (boronic
acids 1 and 3a , boronates 2 and 3b, and trialkylboranes
3c,d ) with iodonium salts 4-6 and iodanes 7 under
aqueous conditions at ambient temperature (Scheme 1,
eq 1).
We first coupled phenylboronic acid (1a ) with diphen-
yliodonium tetrafluoroborate (4a )11 in the presence of Pd-
(PPh3)4 (0.2 mol %) and Na2CO3 (2 equiv) in DME/H2O
X Abstract published in Advance ACS Abstracts, J une 1, 1996.
(1) (a) Suzuki, A. Pure Appl. Chem. 1985, 57, 1749. (b) Suzuki, A.
Ibid. 1991, 63, 419. (c) Suzuki, A. Ibid. 1994, 66, 213. (d) Miyaura,
N.; Suzuki, A. Chem. Rev. 1995, 95, 2457.
(2) (a) Miyaura, N.; Yanagi, T.; Suzuki, A. Synth. Commun. 1981,
11, 513. (b) Ohe, T.; Miyaura, N.; Suzuki, A. Synlett 1990, 221. (c)
Snieckus, V.; Fu, J . Tetrahedron Lett. 1990, 31, 1665. (d) Huth, A.;
Beetz, I.; Schermann, I. Tetrahedron 1989, 45, 6679. (e) Cristofol, W.
A.; Keay, B. A. Tetrahedron Lett. 1991, 32, 5881. (f) Ohe, T.; Miyaura,
N.; Suzuki, A. Synlett 1990, 221. (g) Miyaura, N.; Yamada, K.;
Suginome, H.; Suzuki, A. J . Am. Chem. Soc. 1985, 107, 972.
(3) (a) Campi, E. M.; J ackson, W. R.; Marcuccio, S. M.; Naeslund,
G. M. J . Chem. Soc., Chem. Commun. 1994, 2395. (b) Anderson, J .
C.; Namli, H. Synlett 1995, 765. (c) Uenish, J .-I.; Beau, J .-M.;
Amstrong, R. W.; Kishi, Y. J . Am. Chem. Soc. 1987, 109, 4756.
(4) (a) Varvoglis, A. The Organic Chemistry of Polycoordinated
Iodine; VCH Publishers, Inc.: New York, 1992. (b) Koser, G. F. The
Chemistry of Functional Groups, Supplement D; Patai, D. S., Rapport,
Z., Eds.; Wiley: Chichester, 1983; Chapter 18, p 721. (c) Koser, G. F.
In The Chemistry of Functional Groups, Supplement D; Patai, D. S.,
Rapport, Z., Eds.; Wiley: Chichester, 1983; Chapter 25, p 1265.
(5) For recent reviews: (a) Stang, P. J . Angew. Chem., Int. Ed. Engl.
1992, 31, 274. (b) Moriarty, R. M.; Vaid, R. K. Synthesis 1990, 431.
(c) Ochiai, M. Rev. Heteroatom. Chem. 1989, 2, 92.
(7) Pd-catalyzed C-C bond formation: (a) Moriarty, R. M.; Epa, W.
R.; Awasthi, A. K. J . Am. Chem. Soc. 1991, 113, 6315. (b) Moriarty,
R. M.; Epa, W. R. Tetrahedron Lett. 1992, 33, 4095. (c) Hinkle, R. J .;
Poulter, G. T.; Stang, P. J . J . Am. Chem. Soc. 1993, 115, 11626. (d)
Sugioka, K.; Uchiyama, M.; Suzuki, T.; Yamazuki, Y. Nippon Kagaku
Kaishi 1985, 527, 558; Chem. Abstr. 1986, 104, 108721, 109137. (e)
Kang, S.-K.; J ung, K.-Y.; Park, C.-H.; J ang, S.-B. Tetrahedron Lett.
1995, 36, 8047.
(8) (a) Brown, H. C. Organic Synthesis via Boranes; Wiley: New
York, 1975. (b) Cragg, G. M. L. Organoboranes in Organic Synthesis;
Marcel Dekker: New York, 1973. (c) Pelter, A.; Smith, K. Borane
Reagent; Academic Press: New York, 1988. (d) Brown, H. C.; Gupta,
S. K. J . Am. Chem. Soc. 1972, 94, 4370. (e) Lane, C. F.; Kabalka, G.
W. Tetrahedron 1976, 32, 981. (f) Negishi, E.; William, R. M.; Lew,
G.; Yoshida, T. J . Organomet. Chem. 1975, 92, C4.
(9) For reviews: Martin, A. R.; Yang, Y. H. Acta. Chem. Scand. 1993,
47, 221.
(10) Watanabe, T.; Miyaura, N.; Suzuki, A. Synlett 1992, 207.
(11) Ochiai, M.; Sumi, K.; Takaoka, Y.; Nagao, Y.; Shiro, M.; Fugita,
E. Tetrahedron 1988, 44, 4095.
(6) Moriarty, R. M.; Vaid, R. K.; Koser, G. F. Synlett 1990, 365.
S0022-3263(96)00195-8 CCC: $12.00 © 1996 American Chemical Society

Pd-Catalyzed Cross-Coupling of Organoboron Compounds
Sch em e 1
J . Org. Chem., Vol. 61, No. 14, 1996 4721
Ta ble 1. Rea ction Con d ition s for Cr oss-Cou p lin g of
P h en ylbor on ic Acid w ith Dip h en yliod on iu m
Tetr a flu or obor a te
96% yield (entry 2, Table 1). Since H2O can act as base,
H2O was excluded in the coupling (entry 3, Table 1). It
is noteworthy that coupling can occur even in the absence
of base, as in tin-mediated coupling (Stille reaction).13 To
explain coupling in the absence of base, it is presumed
time yieldc
entry
1
reaction condnsa
(min)
(%)
that PhPd+BF4 is formed as a reactive intermediate in
-
Pd(PPh3)4 (0.2 mol %), Na2CO3,
DME/H2O (4:1),b rt
30
98
the reaction of the iodonium salt 4a and Pd(0) species.7a
The counterion tetrafluoroborate can be used in the
formation of phenylboronate with the Lewis acid phen-
ylboronic acid. Thus, the transmetalation reaction of the
2
3
4
Pd(PPh3)4 (0.2 mol %), DME/H2O (4:1), rt
Pd(PPh3)4 (0.2 mol %), DME, rt
Pd(OAc)2 (0.2 mol %), Na2CO3,
DME/H2O (4:1), rt
30
30
1
96
95
99
phenylboronate and PhPd+BF4 is favored even in the
-
5
6
7
8
Pd(OAc)2 (0.2 mol %), DME/H2O (4:1), rt
Pd(OAc)2 (0.2 mol %), DME, rt
Pd(OAc)2 (0.2 mol %), H2O, rt
Pd/C (2 mol %), Na2CO3, EtOH, rtd
5
5
5
97
95
95
94
absence of base. Comparable yields were achieved when
Pd(PPh3)4 was replaced with Pd(OAc)2, and the reaction
proceeded faster (entries 4-7, Table 1). With Pd(OAc)2
as a catalyst in H2O as a solvent, coupling provided the
biphenyl (8a ) (entry 7, Table 1). Finally, Pd/C (2 mol %)
was used effectively as a source of Pd(0) in this cross-
coupling (entry 8, Table 1).
10
a
The amount of palladium catalyst can be reduced to 0.2 mol
%. However, the yield decreased with 0.1 mol %. At 80 °C, the
reactions were completed within 5 min. Two equiv of base
(Na2CO3 or K2CO3) was used. The coupling reaction did not
b
proceed in the absence of palladium catalysts. Acetone/H2O (4:
4.5) can be used as a solvent with Na2CO3 or K2CO3, or without
B. Cou p lin g of Or ga n ob or on Com p ou n d s w it h
Iod on iu m Sa lts. When we extended this protocol to
other arylboronic acids, unsymmetrical biaryls were
readily obtained in high yields under the same conditions.
The results are summarized in Table 2. Reaction of
substituted arylboronic acid 1b with diphenyliodonium
tetrafluoroborate (4a ) in the presence of Na2CO3 with Pd-
(PPh3)4 as a catalyst in DME/H2O (4:1) at room temper-
ature for 30 min gave the unsymmetrical biaryl 8b
(method A in entry 1, Table 2). Without using base,
comparable yields of biaryl 8b were obtained in 95%
yield. Under the same conditions but with Pd(OAc)2, the
reaction gave the unsymmetrical biaryl 8b (method B).
In the case of Pd(OAc)2, a trace amount of biphenyl (8a )
was obtained as a side product. In the absence of base,
biaryl 8b was obtained in 93% yield. It is known that
d
base, to give comparable yields. c Isolated yields. The addition
of Ph3P to Pd/C decreased the yield.
(4:1) at room temperature to afford biphenyl (8a ) in 98%
yield with high catalytic efficiency (entry 1, Table 1).
Cross-coupling was achieved at ambient temperature.
Although there are few other examples of Suzuki-type
biaryl coupling at ambient temperature, they require the
use of water-soluble aryl iodides and catalyst12 or TlOH
as a base.3 Consistent with the mechanism of the Suzuki
reaction, 2 equiv of base is required. However, high
yields were obtained in the absence of base, even though
base is essential for boron cross-coupling.1,2 The reaction
of phenylboronic acid 1a with Ph2I+BF4 (4a ) in DME/
-
H2O (4:1) without base gave the coupled product 8a in
(12) (a) Bumagin, N. E.; Bykov, V. V.; Beletskaya. Dokl. Akad, Nauk
SSSR 1990, 315, 354 (Engl. Trans.). (b) Genet, J . P.; Linguist, A.; Blart,
E.; Mouries, V.; Savignac, M. Tetrahedron Lett. 1995, 36, 1443.
(13) For reviews: (a) Mitchell, T. W. Synthesis 1992, 803. (b) Stille,
J . K. Angew. Chem., Int. Ed. Engl. 1986, 25, 508.

4722 J . Org. Chem., Vol. 61, No. 14, 1996
Ta ble 2. P d -Ca ta lyzed Cr oss-Cou p lin g of Or ga n ic Bor on Com p ou n d s w ith Iod on iu m Sa ltsa
Kang et al.
a
The reactions were run with arylboronic acid (1.1 equiv), iodonium salt (1 equiv), and Pd(PPh3)4 (0.2 mol %) in the presence of Na2CO3
(2 equiv) in DME/H2O (4:1). The reactions can also be carried out without base. At reflux, the reactions were complete within 5 min.
b
Method A: Pd(PPh3)4 (0.2 mol %). Method B: Pd(OAc)2 (0.2 mol %). The 2-thienyl(phenyl)iodonium tosylate was prepared according to
Koser; see ref 14. c Isolated yields. The yields in parentheses are those obtained in the absence of base.
the cross-coupling of sterically hindered arylboronic acids
proceeds slowly and gives lower yields due to steric
hindrance and competitive hydrolytic deboronation.10 The
reaction of 1-naphthylboronic acid (1f) and mesitylboronic
acid (1g) with iodonium salt 4a proceeded smoothly to
give the coupled biaryls 8f and 8g3b at ambient temper-
ature in almost quantitative yields (entries 5 and 6, Table
2). Similarly, with 2-thienyl(phenyl)iodonium tosylate

Pd-Catalyzed Cross-Coupling of Organoboron Compounds
J . Org. Chem., Vol. 61, No. 14, 1996 4723
(4b),14 the coupling reaction with phenylboronic acid (1a )
gave 2-phenylthiophene (8h )15 as the sole product (entry
7, Table 2). p-Methoxybiphenyl (8b) was obtained (entry
8, Table 2) from (p-methoxyphenyl)(phenyl)iodonium
triflate (4c).16 These results suggest that, in the catalytic
cycle, only electron-donating ArPd+X- formed after lib-
eration of PhI participates in the coupling. This coupling
was also applied to alkenyl- and alkynyliodonium salts11
to give alkenyl- and alkynyl-substituted aromatic com-
pounds 9 and 10a (entries 9 and 10, Table 2). Similarly,
vinylboronic acid 3a was also coupled with diphenyl-
iodonium salt 4a to give 9 (entry 11, Table 2). This
method was successfully applied to organic boronates.
The results are shown in entries 12-16 of Table 2.
Phenylboronate 2a was treated with alkenyl- and alky-
nyliodonium salts 5 and 6a to give trans-stilbene (9) and
disubstituted alkyne 10b in the presence or absence of
base (entries 12 and 13, Table 2).17a Sterically hindered
arylboronate 2b was successfully coupled with diphen-
yliodonium salt 4a to give 8g3b (entry 14, Table 2). For
vinylcatecholboronate 3b, treatment with diphenyl- and
alkenyliodonium salts 4a and 5 gave the coupled products
9 and 11, respectively (entries 15 and 16, Table 2).
Vinyldisiamylborane 3c and trialkylborane 3d were
coupled with diphenyliodonium tetrafluoroborate (4a ) to
give 9 (entries 17 and 18, Table 2).17b
Ta ble 3. P d -Ca ta lyzed Cr oss-Cou p lin g of Or ga n ic Bor on
Com p ou n d s w ith Iod a n esa
Cou p lin g of Or ga n obor on Com p ou n d s w ith Io-
d a n es. We examined the reactions of iodanes in pal-
ladium-catalyzed coupling. Among hypervalent iodine-
(III) compounds, readily available hydroxy(tosyloxy)-
iodobenzene (HTIB) (7a ), PhI(OH)OTs,18 referred to as
Koser’s reagent, has been used in a variety of organic
transformations.6 However, to our knowledge, there have
been no reports of transition metal-catalyzed carbon-
carbon bond formation with iodanes, although there have
been reports of palladium-catalyzed coupling of alkenyl-
iodonium salts with organotin compounds and activated
olefins.7 The palladium-catalyzed C-C coupling of io-
danes is summarized in Table 3.19 Iodane, PhI(OH)OTs,
underwent facile coupling with phenylboronic acid (1a )
in the presence of Pd(PPh3)4 (0.2 mol %) with or without
base to give 8a (entry 1, Table 3). The unsymmetrical
biaryls 8b-f were easily synthesized by cross-coupling
with iodane 7a (entries 2-5, Table 3). The sterically
hindered mesitylboronic acid (1g) coupled smoothly with
iodane 7a in 89% yield (entry 6, Table 3). This coupling
was also applied to the substituted iodane p-CH3OC6H4I-
(OH)OTs (7b),20 which was coupled with phenylboronic
acid and mesitylboronic acid to yield 8b and 8i,21 respec-
tively (entries 7 and 8, Table 3). The iodane PhI(OH)-
a
The reactions were run with arylboronic acid (1.1 equiv),
iodanes (1 equiv), and Pd(PPh3)4 (0.2 mol %) in the presence of
Na2CO3 (2 equiv) in DME/H2O (4:1). The reactions can be carried
out without base. Pd(PPh3)4 gave better results than Pd(OAc)2
in terms of reaction time and yield. In the case of Pd(OAc)2, the
reaction time was 50-60 min. At reflux, the reactions were
b
complete within 5 min. p-CH3OC6H4I(OH)OTs was prepared
according to Koser; see ref 20. c Isolated yields. The yields in
parentheses are those obtained in the absence of base.
OTs was also reacted with vinylcatecholboronate 3b and
mesitylboronate 2b to give the coupled products 9 and
8g in yields of 98 and 91%, respectively (entries 9 and
10, Table 3). Finally, trialkylboranes were used in cross-
coupling to afford trans-stilbene (9) (entries 11 and 12,
Table 3). To explain coupling of iodanes with organobo-
ranes in the absence of base, it is presumed that facile
oxidative addition of iodane with the Pd(0) species gives
the intermediate PhPdOTs bearing a Pd-O bond. This
complex is believed to be polar and more reactive than
organopalladium halide2g for transmetalation with orga-
noborate. The organoborate is supposed to be formed
from boronic acid and counterion hydroxide derived from
iodane. It has been known that the cross-coupling of
organoboron compounds with 1,3-butadiene monoep-
oxide22 and propargylic carbonates23 occurs under neutral
conditions without the need for base.
(14) Margida, A. J .; Koser, G. F. J . Org. Chem. 1984, 49, 3643.
(15) Sotoyama, T.; Hara, S.; Suzuki, A. Bull. Chem. Soc. J pn. 1979,
52, 1865.
(16) Kitamura, T.; Matsuyuki, J .-i.; Nagata, K.; Furuki, R.; Tan-
iguchi, H. Synthesis 1992, 945.
(17) (a) Synthesis of (12R)-HETE by cross-coupling of vinylcat-
echolborane with vinyl iodide: Nicolaou, K. C.; Ramphal, J . Y.; Abe,
Y. Synthesis 1989, 898. (b) Synthesis of LTB4 by cross-coupling of
vinyldisiamylborane with vinyl iodide: Kabayashi, Y.; Shimazaki, T.;
Sato, F. Tetrahedron Lett. 1987, 28, 5849. Kobayashi, Y.; Shimazaki,
T.; Taguchi, H.; Sato, F. J . Org. Chem. 1990, 55, 5324.
(18) (a) Neiland, O.; Karek, B. J . Org. Chem. USSR (Engl. Trans.)
1970, 6, 889. (b) Koser, G. F.; Wettach, R. H. J . Org. Chem. 1977, 42,
1476.
(19) Instead of Koser’s reagent, PhI(OH)OTs, Zefirov’s reagent, can
be used. For the preparation of Zefirov’s reagent, see: Hembre, R. T.;
Scott, C. P.; Norton, J . R. J . Org. Chem. 1987, 52, 3650.
(20) Koser, G. F.; Wettach, R. H. J . Org. Chem. 1980, 45, 1542.
(21) (a) Bell, H. C.; Kalman, J . R.; Pinhey, J . T.; Sternhell, S.
Tetrahedron Lett. 1974, 15, 857. (b) Morgan, J .; Parkinson, C. J .;
Pinhey, J . T. J . Chem. Soc., Perkin Trans. 1 1994, 3361. (c) Norman,
R. O. C.; Thomas, C. B.; Wilson, J . S. J . Chem. Soc., Perkin Trans. 1
1973, 325.
(22) Miyaura, N.; Tanabe, Y.; Suginome, H.; Suzuki, A. J . Orga-
nomet. Chem. 1982, 233, C13.
(23) Moriya, T.; Miyaura, N.; Suzuki, A. Synlett 1994, 149.

4724 J . Org. Chem., Vol. 61, No. 14, 1996
Kang et al.
according to Ochiai et al. 2-Thienyl(phenyl)iodonium tosylate
(4b) was prepared14 according to Margida and Koser. (p-
Methoxyphenyl)(phenyl)iodonium triflate (4c) was prepared16
by the method of Kitamura et al. p-CH3OC6H4I(OH)OTs (7b)
was prepared by known procedures.
Con clu sion
In conclusion, hypervalent iodonium salts and iodanes
can readily undergo palladium-catalyzed cross-coupling
with aryl-, alkenyl-, and alkylboranes under extremely
mild and aqueous conditions at ambient temperature
even in the absence of base. Hypervalent iodine com-
pounds may be soluble in water and act as superior
electrophiles which facilitate the oxidative addition with
Pd(0) to allow coupling under aqueous and mild condi-
tions. We believe that the method described here may
be a valuable alternative to Suzuki and Stille couplings.
Gen er al P r ocedu r e for Cr oss-Cou plin g Reaction s with
Iod on iu m Sa lts: Bip h en yl (8a ). To a mixture of diphenyl-
iodonium tetrafluoroborate (900 mg, 2.45 mmol) and Pd(PPh3)4
(0.2 mol %, 5.70 mg) was added Na2CO3 (518 mg, 2.59 mmol)
under nitrogen atmosphere followed by phenylboronic acid
(328 mg, 2.69 mmol) in DME/H2O (10 mL, 4:1) at room
temperature. The reaction mixture was stirred at room
temperature for 30 min and then quenched with saturated
aqueous NH4Cl. The reaction mixture was extracted with
ether (20 mL × 2), and the organic layer was dried over
anhydrous MgSO4 and evaporated in vacuo. The crude
product was separated by SiO2 column chromatography (hex-
anes, Rf ) 0.47) to afford biphenyl (8a ) (370 mg, 98%): TLC,
SiO2, hexanes, Rf ) 0.47; mp 68.5-69.5 °C (lit.28 mp 69-72
Exp er im en ta l Section
Gen er a l P r oced u r es. All solvents for reactions were
purified before use. IR spectra were recorded on a FT-IR
spectrometer. 1H NMR were conducted at 400 MHz in CDCl3,
1
°C); H NMR (400 MHz, CDCl3) 7.37 (m, 2H), 7.46 (m, 4H),
and chemical shifts are reported in
units relative to the
7.61 (m, 4H); IR (KBr) 3035, 1568, 1480, 730 cm-1; MS (m/e)
154 (M+, base peak), 153, 152, 128, 115, 77, 76, 75. All of the
compounds (8b, 8c, 8d , 8e,27 8f, 8g, 8h , 9, 10a , 10b, and 11
in Table 2) have been previously reported and were prepared
according to procedures in the literature.
tetramethylsilane (TMS) signal at 0.00 ppm. Coupling con-
stants (J ) are reported in Hz. Melting points were determined
in unsealed capillary tubes and are uncorrected. For thin-
layer chromatography (TLC), Merck precoated plates (silica
gel 60 F254, 0.25 mm) were used. Silica gel 60 (9385, 230-
400 mesh) from Merck was used for column chromatography.
The reported yields are for chromatographically pure isolated
products.
Bor on Rea gen ts. Phenylboronic acid (1a ) was purchased
from Aldrich Chemical Co. p-Anisylboronic acid (1b), p-
fluorophenylboronic acid (1c), o-tosylboronic acid (1d ), 2,4-
dichlorophenylboronic acid (1e), and 1-naphthylboronic acid
(1f) were purchased from Lancaster. Mesitylboronic acid (1g)
was easily prepared by hydrolysis of 2b. Mesitylboronate (2b)
was prepared24 from 1-bromo-2,4,6-trimethylbenzene by lithia-
tion followed by treatment of trimethylborate according to
Pinhey’s method. Phenylboronate (2a ) was prepared25 from
bromobenzene by lithiation followed by treatment with tri-
methylborate. (E)- -Styrylboronic acid (3a ) was easily pre-
pared by hydrolysis of 3b. (E)- -Styrylcatecholborane (3b) was
prepared8b from catecholborane (1,3,2-benzodioxaborole) and
phenylacetylene according to Brown’s method. (E)- -Styryl-
disiamylborane (3c) was prepared8a,c via the hydroboration of
phenylacetylene with disiamylborane-THF and was used
without further purification. (E)-1-(9-BBN-9-yl)-2-phenylethene
(3d ) was prepared26 by hydroboration of phenylacetylene with
9-BBN.
Gen er al P r ocedu r e for Cr oss-Cou plin g Reaction s with
Iod a n es: Bip h en yl (8a ). To a mixture of hydroxy(tosyloxy)-
iodobenzene (HTIB) (960 mg, 2.45 mmol) and Pd(PPh3)4 (0.2
mol %, 5.70 mg) was added Na2CO3 (518 mg, 2.59 mmol) under
nitrogen atmosphere followed by phenylboronic acid (328 mg,
2.69 mmol) in DME/H2O (10 mL, 4:1) at room temperature.
The reaction mixture was stirred at room temperature for 35
min and then quenched with saturated NH4Cl solution. The
reaction mixture was extracted with ether (20 mL × 2), and
the organic layer was dried over anhydrous MgSO4 and
evaporated in vacuo. The crude product was separated by SiO2
column chromatography (hexanes, Rf ) 0.47) to give biphenyl
(8a ) (355 mg, 94%): TLC, SiO2, hexanes, Rf ) 0.47; mp 68.5-
69.5 °C (lit.28 mp 69-72 °C); 1H NMR (400 MHz, CDCl3) 7.37
(m, 2H), 7.46 (m, 4H), 7.61 (m, 4H); IR (KBr) 3035, 1568, 1480,
730 cm-1; MS (m/e) 154 (M+, base peak), 153, 152, 128, 115,
77, 76, 75. All of the compounds (8a , 8b, 8c, 8d , 8f, 8g, 8i,
and 9 in Table 2) have been previously reported and were
prepared according to procedures in the literature.
Ack n ow led gm en t. The generous financial support
of KOSEF-OCRC and the Ministry of Education (BSRI-
95-3420) is gratefully acknowledged.
Iod on iu m Sa lts a n d Iod a n es. Hydroxy(tosyloxy)iodoben-
zene (7a ) was purchased from Aldrich Chemical Co. Diphen-
yliodonium tetrafluoroborate (4a ), alkenyliodonium salt (5),
and alkynyliodonium salts (6a and 6b ) were prepared11
Su p p or tin g In for m a tion Ava ila ble: Experimental pro-
cedures and spectral and analytical data for the compounds
(3 pages). This material is contained in libraries on microfiche,
immediately follows this article in the microfilm version of the
journal, and can be ordered from the ACS; see any current
masthead page for ordering information.
(24) Morgan, J .; Pinhey, J . T. J . Chem. Soc., Perkin Trans. 1 1990,
715.
(25) (a) Bean, F. R.; J ohnson, J . R. J . Am. Chem. Soc. 1932, 54, 4415.
(b) Wang, M. S.; Nicoud, J . F. Tetrahedron Lett. 1993, 34, 8237.
(26) (a) Brown, H. C.; Scouten, C. G.; Liotta, R. J . Am. Chem. Soc.
1979, 101, 96. (b) Wang, K. K.; Scouten, C. G.; Brown, H. C. J . Am.
Chem. Soc. 1982, 104, 531.
J O960195M
(27) J ulliard, M.; Vernin, G.; Metzger, J . Helv. Chim. Acta 1980,
63, 456.
(28) Budavari, S.; O’Neil, M. J .; Smith, A.; Hevkelman, P. E. In The
Merck Index, 11th ed.; Merck & Co., Inc.: Rahway, NJ , 1989; p 3314.