Triethylborane-mediated hydrogallation and hydroindation: Novel access to organogalliums and organoindiums

Article abstract of DOI:10.1021/jo0344790

Hydrogallation of carbon-carbon multiple bonds proceeds in the presence of triethylborane as a radical initiator. Several functionalities do not interfere with this reaction. Resulting alkenyl- and alkylgallium species can be trapped by several electrophiles. Highly regioselective radical addition of an indium hydride reagent to alkynes is also achieved. Various functionalities are tolerant under the reaction conditions. The reaction proceeds with complete anti stereoselectivity. Alkenylindiums obtained via hydroindation can be employed for the following cross-coupling reaction with aryl halides in one pot.

Full text of DOI:10.1021/jo0344790

Tr ieth ylbor a n e-Med ia ted Hyd r oga lla tion a n d Hyd r oin d a tion :
Novel Access to Or ga n oga lliu m s a n d Or ga n oin d iu m s
Kazuaki Takami, Satoshi Mikami, Hideki Yorimitsu, Hiroshi Shinokubo, and
Koichiro Oshima*
Department of Material Chemistry, Graduate School of Engineering, Kyoto University,
Kyoto 606-8501, J apan
oshima@fm1.kuic.kyoto-u.ac.jp
Received April 15, 2003
Hydrogallation of carbon-carbon multiple bonds proceeds in the presence of triethylborane as a
radical initiator. Several functionalities do not interfere with this reaction. Resulting alkenyl- and
alkylgallium species can be trapped by several electrophiles. Highly regioselective radical addition
of an indium hydride reagent to alkynes is also achieved. Various functionalities are tolerant under
the reaction conditions. The reaction proceeds with complete anti stereoselectivity. Alkenylindiums
obtained via hydroindation can be employed for the following cross-coupling reaction with aryl
halides in one pot.
In tr od u ction
well-investigated. Herein we wish to report triethylbo-
rane-mediated7 hydrogallation and hydroindation reac-
tions of carbon-carbon multiple bonds.
Hydroboration and hydroalumination are reliable ways
to reduce carbon-carbon multiple bonds.1 In addition,
alkenyl- and alkylmetals formed via hydrometalation are
versatile reagents which can be utilized in various
reactions. However, hydroboration and hydroalumination
usually proceed in a syn fashion. For instance, hydrobo-
ration of alkynes always provides (E)-alkenylboranes
selectively. Preparation of (Z)-alkenylboranes from alkynes
needs several steps.2 Moreover, it is necessary to protect
functionalities such as hydroxy and carboxy groups before
performing hydroboration. Operationally simple methods
which are widely adaptable for the preparation of various
(Z)-alkenylmetals from alkynes are limited. In the mean-
time, gallium3-5 and indium6 hydride reagents were not
Resu lts a n d Discu ssion
Hyd r oga lla tion of Alk yn es. The gallium hydride
reagent (HGaCl2) was prepared by mixing a hexane
solution of gallium trichloride (1.0 M, 1.5 mL, 1.5 mmol)
and a toluene solution of Red-Al (2.0 M, 0.375 mL, 0.75
mmol) in THF at 0 °C (Scheme 1).8 To the solution were
added 1-dodecyne (1.0 mmol) and triethylborane (0.20
mmol). After 4 h, the reaction was quenched with 1.0 M
HCl. Silica gel column purification provided 1-dodecene
in 84% yield. An addition of 1.0 M DCl/D2O instead of
hydrochloric acid to the reaction mixture afforded 1-deu-
terio-1-dodecene in 84% yield as a mixture of stereoiso-
mers (E/Z ) 80/20). The choice of DIBAL-H as a reducing
(1) (a) Pelter, A.; Smith, K.; Brown H. C. Borane Reagents; Academic
Press: London, UK, 1988. (b) Seyden-Penne, J . Reductions by the
Alumino- and Borohydrides in Organic Synthesis; VCH: New York,
1991. (c) Comprehensive Organic Chemistry; Pergamon Press: New
York, 1979; Vol. 8.
(2) (a) Brown, H. C.; Imai, T. Organometallics 1984, 3, 1392-1395.
(b) Negishi, E.; Williams, R. M.; Lew, G.; Yoshida, T. J . Organomet.
Chem. 1975, 92, C4-C6. (c) Campbell, J . B., J r.; Molander, G. A. J .
Organomet. Chem. 1978, 156, 71-79. (d) Srebnik, M.; Bhat, N. G.;
Brown, H. C. Tetrahedron Lett. 1988, 29, 2635-2638. (e) Deloux, L.;
Srebnik, M. J . Org. Chem. 1994, 59, 6871-6873. (f) Takahashi, K.;
Takagi, J .; Ishiyama, T.; Miyaura, N. Chem. Lett. 2000, 126-127.
(3) Reduction of alkynes with gallium hydride compounds was
reported. Ohshita, J .; Schmidbaur, H. J . Organomet. Chem. 1993, 453,
7-12.
(4) Reduction of organic halides and carbonyl compounds with
MGaH4 (M ) Li, Na, K) was reported. (a) Schmidba, H.; Findeiss, W.;
Gast, E. Angew. Chem., Int. Ed. Engl. 1965, 4, 152. (b) Choi, J . H.;
Yun, J . H.; Hwang, B. K.; Baek, D. J . Bull. Korean Chem. Soc. 1997,
18, 541-542. (c) Kim, J . S.; Choi, J . H.; Kim, H. D.; Yun, J . H.; J oo, C.
Y.; Baek, D. J . Bull. Korean Chem. Soc. 1999, 20, 237-240. (d) Choi,
J . H.; Yoon, Y. G. Bull. Korean Chem. Soc. 1995, 16, 469-470. (e) Choi,
J . H.; Oh, Y. J . Bull. Korean Chem. Soc. 1995, 16, 474-475. (f) Choi,
J . H.; Yoon, M. Y.; Yun, J . H.; Chung, D. W. Bull. Korean Chem. Soc.
1995, 16, 416-421. Review on gallium hydrides: (g) Barron, A. R.;
MacInnes, A. N. In Encyclopedia of Inorganic Chemistry, King, R. B.,
Ed.; J ohn Wiley & Sons: Chichester, UK, 1994; Vol. 3, p 1249.
(5) Triethylborane-mediated radical reduction of organic halides
with the gallium hydride reagent was reported. Mikami, S.; Fujita,
K.; Nakamura, T.; Yorimitsu, H.; Shinokubo, H.; Matsubara, S.;
Oshima, K. Org. Lett. 2001, 3, 1853-1855.
(6) (a) Wiberg, E.; Schmidt, M. Z. Naturforsch. 1957, 12b, 54-58.
(b) Yamada, M.; Tanaka, K.; Araki, S.; Butsugan, Y. Tetrahedron Lett.
1995, 36, 3169-3172. (c) Takami, K.; Yorimitsu, H.; Oshima, K. Org.
Lett. 2002, 4, 2993-2995. (d) Miyai, T.; Inoue, K.; Yasuda, M.; Shibata,
I.; Baba, A. Tetrahedron Lett. 1998, 39, 1929-1932. (e) Inoue, K.;
Yasuda, M.; Shibata, I.; Baba, A. Tetrahedron Lett. 2000, 41, 113-
116. (f) Inoue, K.; Shibata, I.; Baba, A. Tetrahedron Lett. 2001, 42,
4661-4663. (g) Inoue, K.; Sawada, A.; Shibata, I.; Baba, A. J . Am.
Chem. Soc. 2002, 124, 906-907. (h) Inoue, K.; Ishida, T.; Shibata, I.;
Baba, A. Adv. Synth. Catal. 2002, 344, 283-287. (i) Ranu, B. C.;
Samanta, S. Tetrahedron Lett. 2002, 43, 7405-7407.
(7) (a) Nozaki, K.; Oshima, K.; Utimoto, K. J . Am. Chem. Soc. 1987,
109, 2547-2548. (b) Oshima, K.; Utimoto, K. J . Synth. Org. Chem.,
J pn. 1989, 47, 40-52. (c) Yorimitsu, H.; Oshima, K. In Radicals in
Organic Synthesis; Renaud, P., Sibi, M. P., Eds.; Wiley-VCH: Wein-
heim, Germany, 2001; Chapter 1.2. (d) Ollivier, C.; Renaud, P. Chem.
Rev. 2001, 101, 3415-3434.
(8) We have not succeeded in obtaining the spectral evidence of
HGaCl2 at this stage. See also ref 13.
10.1021/jo0344790 CCC: $25.00 © 2003 American Chemical Society
Published on Web 07/22/2003
J . Org. Chem. 2003, 68, 6627-6631
6627

Takami et al.
SCHEME 1
suggests that the reaction initially provides (Z)-alkenyl-
gallium, which then isomerizes to its (E)-isomer. A
plausible mechanism is depicted in Scheme 2. A gallium
radical (•GaCl2), generated by the action of an ethyl
radical on HGaCl2, adds to 1-alkyne to afford alkenyl
radical 3. Radical 3 isomerizes into 4. Hydrogen donation
to 3 rather than to 4 is kinetically preferred because
radical 3 is more accessible for gallium hydride as
depicted in drawing A, thereby yielding (Z)-alkenylgal-
lium 5 as a major product at the initial stage of the
reaction. Isomerization into the (E)-alkenylgallium com-
pound proceeds via a gallium radical addition-elimina-
tion sequence:9 An addition of the gallium radical to (Z)-
alkenylgallium 5 provides a dimetallic radical species 7
or 8. Rotation around the CR-Câ bond followed by
elimination of the gallium radical enables conversion into
the more thermodynamically stable (E)-alkenylgallium
species 6.
TABLE 1. Hyd r oga lla tion of Alk yn esa
Cr oss-Cou p lin g Rea ction of Ar yl Ha lid es w ith
Alk en ylga lliu m s P r ep a r ed via H yd r oga lla t ion of
Alk yn es. Next, we tried to employ the alkenylgalliums
provided via hydrogallation for the following cross-
coupling reaction10 in one pot (Scheme 3). HGaCl2 (3.0
mmol) prepared as aforementioned was treated with
1-dodecyne (1.5 mmol) and triethylborane (0.30 mmol)
to prepare an alkenylgallium species. After removal of
THF by reducing pressure, DMSO (5 mL), 3-iodoanisole
(1.0 mmol), and palladium catalyst11 were sequentially
added. Heating the resulting mixture at 80 °C for 4 h
afforded the cross-coupling products 9a (E/Z ) 66/34, 31%
yield) and 10a (18% yield). Not only 3-iodoanisole but also
3-iodophenol could be employed in this cross-coupling
reaction.
a
Alkyne (1.0 mmol), Et3B (0.20 mmol), and THF (5 mL) were
used. Isolated yields. E/Z ratios are in parentheses. c Reaction
was quenched with iodine.
b
H yd r oga lla t ion of Alk en es. The radical addition
of HGaCl2 to 1-alkenes proceeded similarly to yield
alkylgallium species (Scheme 4). In contrast to the
case with alkynes, hydrolysis of the resultant alkyl-
gallium compounds required forcing reaction condi-
tions. After hydrogallation of 1-dodecene, an excess of
methyllithium (9.0 equiv) was added to the reaction
mixture. Subsequent exposure to concentrated hydro-
chloric acid (37 wt %) for 1 h provided dodecane in 85%
yield. On the other hand, the reaction of an internal
alkene, such as 6-dodecene, provided none of hydrogal-
lation products.
agent instead of Red-Al provided 1-deuterio-1-dodecene
(84% yield) with a slightly lower selectivity (E/Z ) 77/
23). Without triethylborane, the reaction did not proceed
at all. In addition, a catalytic amount of TEMPO (2,2,6,6-
tetramethylpiperidin-1-oxyl) inhibited the reaction com-
pletely. These results strongly suggest that the reaction
proceeds via a radical mechanism.
Various alkynes can be employed in this hydrogallation
reaction. The results are summarized in Table 1. It is
noteworthy that functional groups such as ether and
ester moieties did not interfere with the triethylborane-
induced reduction, whereas hydroalumination often re-
quires the absence of such coordinating groups. Hydro-
gallation of internal alkynes also proceeded smoothly,
although the products were obtained as a mixture of E/Z
isomers.
To clarify the reaction course, the reaction of 1-dode-
cyne with the gallium hydride was investigated in detail.
We found that the stereochemical outcome of the product
heavily depended on the reaction time. Quenching the
reaction with 1.0 M DCl/D2O after 2.5 h provided 1-deu-
terio-1-dodecene in 55% yield as a mixture of stereoiso-
mers (E/Z ) 28/72). The E/Z ratios of 1-deuterio-1-
dodecene varied depending on the reaction time, and the
ratios were E/Z ) 56/44 at 3.0 h (61% yield) and E/Z )
80/20 at 4.0 h (84% yield). The change of the E/Z ratios
Hydrogallation of allenes provided allylic gallium
compounds. The addition of the gallium radical mainly
occurred at the terminal carbon (Scheme 5). Diene 11 was
obtained as a byproduct via dimerization of an allylic
radical generated by the attack of the gallium radical at
the 2 position. The allylic gallium reagent prepared by
this method reacted with electrophiles, such as D2O and
benzaldehyde, to provide the corresponding products in
moderate yields.12
(9) The same isomerization reaction of alkenyl germanes has been
reported. Ichinose, Y.; Nozaki, K.; Wakamatsu, K.; Oshima, K.;
Utimoto, K. Tetrahedron Lett. 1987, 28, 3709-3712.
(10) Mikami, S.; Yorimitsu, H.; Oshima, K. Synlett 2002, 7, 1137-
1139.
(11) The palladium catalyst was prepared from Pd2(dba)3‚CHCl3
(0.010 mmol) and tri-o-tolylphosphine (0.040 mmol) in DMSO (1 mL)
in another reaction flask under an argon atmosphere.
6628 J . Org. Chem., Vol. 68, No. 17, 2003

Hydrogallation and Hydroindation
SCHEME 2
SCHEME 3
SCHEME 4
Hyd r oin d a tion of Alk yn es. Treatment of InCl3 (1.35
mmol) in THF with DIBAL-H (1.30 mmol) at 0 °C yielded
dichloroindium hydride (HInCl2).13 To the solution were
sequentially added at -78 °C 1-dodecyne (1.0 mmol) and
a catalytic amount of triethylborane (0.20 mmol) as a
radical initiator. The resulting solution was stirred for
2.5 h at the same temperature. Acidic workup followed
by silica gel column purification provided 1-dodecene
almost quantitatively (Scheme 6). Hydroindation of
1-dodecyne proceeded in an anti fashion to yield (Z)-1-
dodecenylindium. Quenching with 1.0 M DCl/D2O yielded
(Z)-1-deuterio-1-dodecene exclusively (96%D, E/Z < 1/99).
Iodolysis of the reaction mixture also afforded the cor-
responding (Z)-isomer selectively14 in 92% yield. Using
Red-Al in place of DIBAL-H resulted in a much lower
(13) 1H NMR measurements revealed the formation of HInCl2. The
hydride attached to the aluminum of DIBAL-H appeared at δ 3.8 ppm
(broad) in THF-d8. A new broad signal (δ 6.8 ppm) was observed after
treatment of InCl3 with DIBAL-H. Baba reported that the hydride of
HInCl2, prepared from InCl3 and n-Bu3SnH, appeared at δ 6.5 ppm.
See: Miyai, T.; Inoue, K.; Yasuda, M.; Shibata, I.; Baba, A. Tetrahedron
Lett. 1998, 39, 1929-1932. However, Baba’s HInCl2 did not add to
alkynes. The reason for the different reactivity is not clear. Diisobu-
tylaluminum chloride might coordinate to HInCl2, thereby changing
the reactivity.
(12) Reactions of allylic gallium species were reported. (a) Han, Y.;
Huang, Y.-Z. Tetrahedron Lett. 1994, 35, 9433-9434. (b) Han, Y.; Chi,
Z.; Huang, Y.-Z. Synth. Commun. 1999, 29, 1287-1296. (c) Araki, S.;
Ito, H.; Butsugan, Y. Appl. Organomet. Chem. 1988, 2, 475-478. (d)
Tsuji, T.; Usugi, S.; Yorimitsu, H.; Shinokubo, H.; Matsubara, S.;
Oshima, K. Chem. Lett. 2002, 2-3.
J . Org. Chem, Vol. 68, No. 17, 2003 6629

Takami et al.
SCHEME 5
TABLE 2. Hyd r oin d a tion of Alk yn es F ollow ed by
SCHEME 6
Iod olysisa
b
entry
14
R
15
yield/%
E/Z
1
14a
14a
14b
14c
14d
14e
14f
14g
14h
PhCH2O(CH2)3
PhCH2O(CH2)3
EtOOC(CH2)6
HO(CH2)4
15a
15a
15b
15c
15d
15e
15f
15g
15h
79
91
99
78
57
73
98
74
99
1/99
2/98
2c
3
<1/99
<1/99
<1/99
<1/99
3/97
yield (11% yield, E/Z < 1/99). When the reaction was
performed without triethylborane, 1-dodecene was pro-
duced in only 34% yield.15 Furthermore, TEMPO inhib-
ited the reaction (0.20 equiv, 48% yield; 0.40 equiv, 10%
yield). These observations suggest that the reaction
involves a radical mechanism.
4
5
6
7
HOCH2
n-C4H9CO(CH2)6
HOOC(CH2)6
CH2dCH(CH2)8
Ph
8
1/99
7/93
9c
a
Alkyne (1.0 mmol), HInCl2 (1.3 mmol), and Et3B (0.20 mmol)
We assume that the reaction proceeds via a radical
addition of indium hydride reagent across a carbon-
carbon triple bond.16 (Z)-Alkenylidium dichloride that is
initially formed does not isomerize to the (E)-isomer,
because of the very low reactivity of dichloroindium
radical toward the alkenylindium.17 If the second addition
of the indium radical occurs, isomerization of (Z)-alk-
enylindium compound into its thermodynamically stable
(E)-form proceeds via the diindium species.
b
were used. Determined by 1H NMR. c The reaction was per-
formed at -40 °C.
SCHEME 7
A variety of alkynes were subjected to the hydro-
indation reaction and following iodolysis (Table 2). Note-
worthy is the fact that many functionalities including
hydroxy, carbonyl, and carboxy groups did not inter-
fere with the reaction (entries 3-7). The hydroinda-
tion proceeded much faster at the alkynyl moiety than
at the alkenyl group to yield iodo diene 15g selectively
starting from enyne 14g (entry 8). An addition to phe-
nylacetylene yielded a mixture of E/Z isomers with
slightly lower selectivity (7/93, entry 9). None of the
desired product was obtained in the reaction of trimeth-
ylsilylacetylene.
suggests that this hydroindation reaction proceeds in a
radical mechanism. Namely, a radical addition of the
indium-centered radical to the alkyne moiety of 16
produces vinyl radical 18. Radical cyclization of 18 yields
methylenecyclopentane 19. Hydride abstraction from
dichloroindium hydride followed by acidic workup affords
17.
Cr oss-Cou p lin g Rea ction of Ar yl Ha lid es w ith
Alk en ylin d iu m s P r ep a r ed via Hyd r oin d a tion . In-
creasing attention has been paid to the cross-coupling
reaction of organic halides with organoindiums.18 How-
ever, most organoindium reagents were prepared from
indium trichloride and the corresponding organolithium
or -magnesium reagents. With the protocol to prepare
alkenylindiums in hand, we investigated the cross-
coupling reaction of aryl halides with alkenylindiums in
one pot. After optimization of the reaction conditions, a
DMI (1,3-dimethylimidazolidin-2-one)/THF mixed solvent
system proved to be effective in obtaining the coupling
Interestingly, treatment of enyne 16 with HInCl2 and
Et3B at 25 °C afforded the corresponding cyclized product
17 in 30% yield (Scheme 7). The formation of 17 strongly
(14) The hydroindation reaction at 0, -10, and -40 °C yielded a
mixture of stereoisomers (E/Z ) 20/80, 6/94, and 3/97, respectively)
after iodolysis.
(15) Indium hydride spontaneously induces the radical reaction. See
ref 16. Moreover, some organoaluminum compounds can initiate a
radical reaction. See: Chakraborty, A.; Marek, I. Chem. Commun.
1999, 2375-2376.
(16) Reduction of organic halides via a radical process was recently
reported. Inoue, K.; Sawada, A.; Shibata, I.; Baba, A. J . Am. Chem.
Soc. 2002, 124, 906-907.
(17) (a) Ichinose, Y.; Nozaki, K.; Wakamatsu, K.; Oshima, K.;
Utimoto, K. Tetrahedron Lett. 1987, 28, 3709-3712. (b) Nozaki, K.;
Ichinose, Y.; Wakamatsu, K.; Oshima, K.; Utimoto, K. Bull. Chem. Soc.
J pn. 1990, 63, 2268-2272. (c) Taniguchi, M.; Nozaki, K.; Miura, K.;
Wakamatsu, K.; Oshima, K.; Utimoto, K. Bull. Chem. Soc. J pn. 1992,
65, 349-354. (d) Chatgilialoglu, C.; Ballestri, M.; Ferreri, C.; Vecchi,
D. J . Org. Chem. 1995, 60, 3826-3831.
6630 J . Org. Chem., Vol. 68, No. 17, 2003

Hydrogallation and Hydroindation
TABLE 3. On e-P ot Hyd r oin d a tion /Cr oss-Cou p lin g Rea ction a
entry
14
R
Ar
20
yield/%
E/Zb
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
14i
14i
14i
14i
14i
14i
14i
14i
14b
14b
14j
14j
14c
14c
14c
14a
14k
n-C6H13
n-C6H13
n-C6H13
n-C6H13
n-C6H13
n-C6H13
n-C6H13
n-C6H13
C2H5OOC(CH2)6
C2H5OOC(CH2)6
TBSO(CH2)3
TBSO(CH2)3
HO(CH2)4
HO(CH2)4
HO(CH2)4
PhCH2O(CH2)3
PhCH2OCH2
Ph
20a
20b
20c
20d
20e
20f
20g
20h
20i
20j
20k
20l
20m
20n
20o
20p
20q
94
98
99
91
89
75
68
46
92
99
70
90
99
99
36
91
78
5/95
5/95
5/95
C6H4-2-NO2
C6H4-4-NO2
C6H4-2-CO2-n-C4H9
C6H4-3-OCH3
2-pyridyl
C6H4-4-CH3
C6H4-3-OH
Ph
5/95
5/95c
3/97c
4/96
1/99
3/97
5/95
2/98
5/95
2/98
C6H4-4-NO2
Ph
d
d
C6H4-4-NO2
C6H4-4-NO2
C6H4-3-OCH3
C6H4-3-OH
C6H4-3-OCH3
C6H4-3-OCH3
3/97c
3/97c
20/80e
11/89e
a
Alkyne (1.3 mmol), InCl3 (1.55 mmol), DIBAL-H (1.50 mmol), Et3B (0.20 mmol), aryl iodide (1.0 mmol), and Pd cat. (0.50 mol %) were
used. Determined by 1H NMR. c Hydroindation was performed at -40 °C. TBS ) t-BuMe2Si. e Hydroindation was performed at 0 °C.
b
d
Con clu sion
products. DMI (3 mL) was added to a THF solution of
We have revealed novel reactivities of gallium and
indium hydride reagents. The gallium hydride reagent
undergoes a facile addition to alkynes and alkenes. The
reaction tolerates the existence of various functional
groups. Organogallium species obtained with the present
protocol can be trapped with some electrophiles. Trieth-
ylborane-induced hydroindation of alkynes proceeds in
an anti manner to afford the corresponding (Z)-alk-
enylindium species. This method allows us to employ
unprotected alkynes as (Z)-alkenylmetal precursors and
to synthesize functionalized (Z)-alkenyl iodides and (Z)-
arylalkenes in a one-pot operation with high stereose-
lectivity.
the (Z)-1-octenylindium reagent (1.3 mmol) prepared via
hydroindation as aforementioned. An addition of iodo-
benzene (1.0 mmol) and palladium-trifurylphosphine
complex (0.50 mol %)19 followed by heating the whole
mixture at 66 °C for 30 min afforded â-hexylstyrene (20a ,
E/Z ) 5/95) in 94% yield. Various combinations of alkynes
and aryl iodides were examined as listed in Table 3. High
stereoselectivity was accomplished in all cases. Namely,
the cross-coupling reaction process retained the stereo-
chemistry of the alkenylindiums. Several functional
groups both in alkynes and in aryl iodides were compat-
ible in this one-pot reaction. In particular, coupling of
5-hexyn-1-ol with 3-iodoanisole represents the usefulness
of the present strategy (entry 14).
Ack n ow led gm en t. This work was supported by
Grants-in-Aid for Scientific Research (Nos. 12305058
and 10208208) and a Grant-in-Aid for Scientific Re-
search on Priority Areas (No. 14078215) from the
Ministry of Education, Science Sports, and Culture,
J apan. H.Y. acknowledges the J SPS Research Fellow-
ship for Young Scientists.
(18) (a) Pe´rez, I.; Pe´rez Sestelo, J .; Sarandeses, L. A. Org. Lett. 1999,
1, 1267-1269. (b) Gelman, D.; Schumann, H.; Blum, J . Tetrahedron
Lett. 2000, 41, 7555-7558. (c) Fujiwara, N.; Yamamoto, Y. J . Org.
Chem. 1999, 64, 4095-4101. (d) Hirashita, T.; Yamamura, H.; Kawai,
M.; Araki, S. Chem. Commun. 2001, 387-388. (e) Pe´rez, I.; Pe´rez
Sestelo, J .; Sarandeses, L. A. J . Am. Chem. Soc. 2001, 123, 4155-
4160. (f) Lee, P. H.; Sung, S.; Lee, K. Org. Lett. 2001, 3, 3201-3204.
(g) Takami, K.; Yorimitsu, H.; Shinokubo, H.; Matsubara, S.; Oshima,
K. Org. Lett. 2001, 3, 1997-1999.
Su p p or tin g In for m a tion Ava ila ble: General procedures
and spectral data for all compounds. This material is available
free of charge via the Internet at http://pubs.acs.org.
(19) The palladium catalyst was prepared from Pd2(dba)3‚CHCl3
(0.0025 mmol) and P(2-furyl)3 (0.015 mmol) in THF (1.0 mL) in another
reaction flask under an argon atmosphere.
J O0344790
J . Org. Chem, Vol. 68, No. 17, 2003 6631