Nickel(0)-catalyzed three-component connection reaction of dimethylzinc, 1,3-dienes, and carbonyl compounds

Article abstract of DOI:10.1002/(SICI)1521-3773(19991115)38:22<3386::AID-ANIE3386>3.0.CO;2-W

Linear 1:1:1 coupling of dimethylzinc, 1,3-dienes, and carbonyl compounds in this order is facilitated by catalytic amounts of [Ni(acac)₂] to give (E)-3-hexen-1-ols in good yields under mild conditions [Eq. (a)]. Increasing steric hindrance at the carbonyl group favors formation of the 1:2:1 adduct, and this is the sole product when the carbonyl compound is acetone, acac = acetylacetonate.

Full text of DOI:10.1002/(SICI)1521-3773(19991115)38:22<3386::AID-ANIE3386>3.0.CO;2-W

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[
[
10] B. Westermann, I. Gedrath, Synlett 1996, 665 ± 666.
11] J. E. Baldwin, R. M. Adlington, D. W. Gollins, C. J. Schofield,
Tetrahedron 1990, 46, 4733 ± 4748.
12] Compound (Æ)-6 can be obtained from 2-ethylcyclopentanon-2-ethyl
carboxylate and hydroxylamine [(Æ)-7: E:Z > 50:1] and subsequent
esterification with butyryl chloride.
R"
R'
R"
R'
R"
R'
O
O
MRn–1
O
NiII
[
[
[
NiII
MRn
Ni0
I
MRn
R
R = Me
R = Et
Ni0
13] The enantiomeric excesses were determined by GC (Lipodex b-PM,
Macherey-Nagel) for (‡)-7 and (� )-7 and by HPLC (Chiraldex OB-
H, Baker) for (� )-6.
Ni0
H2C=CH2
14] R. Pulido, V. Gotor, J. Chem. Soc. Perkin Trans. 1 1993, 589 ± 592; M.
Murukata, M. Imai, M. Tamura, O. Hoshino, Tetrahedron: Asymmetry
R"
R"
Me
Me
R'
R'
R'
1
994, 5, 2019 ± 2024.
15] P. Peterli-Roth, M. P. Maguiere, E. Leon, H. Rapoport, J. Org. Chem.
994, 59, 4186 ± 4193.
R"
R"
O
Me
O
H
O
MMen–1
MEtn–1
[
[
[
MMen–1
1
13
16] In addition, the C NMR spectra for (Æ)-12b indicated an epimeric
mixture of products
R"
R"
H
17] U. Sprengard, G. Kretzschmer, E. Bartnik, C. Huls, H. Kunz, Angew.
Chem. 1995, 107, 1104 ± 1107; Angew. Chem. Int. Ed. Engl. 1995, 34,
R'
OH
R'
R'
Me OH
OH
990 ± 992; S. Nishimura, M. Matsuda, H. Kitamura, T. Nishimura,
2
7
1
Chem. Commun. 1999, 1435 ± 1436.
Scheme 1. Nickel-catalyzed coupling of 1,3-dienes with alkylmetal re-
agents and carbonyl compounds.
reductive elimination to furnish 1 and ethylene and regener-
0
ate Ni .
Nickel(0)-Catalyzed Three-Component
Connection Reaction of Dimethylzinc,
This sequence of reactions suggested to us that if di-
methylzinc were used in place of diethylzinc, the b-dehydro-
nickelation in the final step might be inhibited, and the
intermediates I (R ˆ Me) would undergo reductive elimina-
tion to provide homoallyl alcohols 2 or bis-homoallyl alcohols
1
,3-Dienes, and Carbonyl Compounds**
Masanari Kimura, Shintaro Matsuo, Kazufumi Shibata,
and Yoshinao Tamaru*
7
(
[
. In fact, when dimethylzinc (4.8 mmol), 1,3-butadiene
8.0 mmol), and benzaldehyde (2.0 mmol) were exposed to
Ni(acac) ] (0.2 mmol) in dry THF (5 mL) at room temper-
Since the discoveries of the thermal [4‡2] cycloaddition
2
reaction by Diels and Alder and nickel-catalyzed oligomeri-
ature for 2 h under N , the methyl group was transferred
2
[
1]
zation by Wilke, 1,3-dienes have been recognized to be
among the most useful synthetic blocks in organic synthesis.
Significant expansion of their synthetic utility has been
brought about by recent studies on transition metal catalyzed
selectively to the distal allylic terminus, and homoallyl alcohol
2
a (R' ˆ Ph, R'' ˆ H in Scheme 1) was obtained in almost
quantitative yield [Eq. (a), R ˆ Ph; Table 1, entry 1]. In the
product mixture, the corresponding regioisomeric product 7
[
2]
cyclizations and 1,2-/1,4-difunctionalization of 1,3-dienes (H,
[14]
(R' ˆ Ph, R'' ˆ H) was not detected at all.
[
3]
[4]
[5]
[6]
[7]
[8]
[9]
[10]
B; H, Si; H, Sn; B, B ; B, Si; B, Sn; C, Si; Si, Si;
[
11]
[12]
Sn, Sn; etc.). In most cases, the products of the latter
reactions are allylic metalloids that are capable of regio- and
stereoselective allylation of carbonyl compounds.
O
0.1 [Ni(acac)2]
Me2Zn
+
+
(a)
R
THF, 25–30 °C
OH
R
OH
We previously reported that, in the presence of a catalytic
amount of [Ni(acac) ] (acac ˆ acetylacetonato) and a stoich-
R
2
iometric amount of triethylborane or diethylzinc, 1,3-dienes
serve as a homoallyl anion equivalent and react with a wide
range of carbonyl compounds to furnish bishomoallyl alcohols
2
3
A number of nickel-catalyzed three-component connection
in high yields and with high regio- and stereoselectivities[
13]
reactions between organometallic compounds, alkynes (or
strained alkenes), and carbonyl compounds have been
reported;[ however, the present reaction, to the best of
our knowledge, is the first example that utilizes conjugated
dienes as the unsaturated hydrocarbon component.[ Al-
1
(Scheme 1). A proposed mechanism involves nucleophilic
15]
addition of diene ± nickel(0) complexes to carbonyl com-
pounds coordinated by MR (MR ˆ Et Zn or Et B) and ethyl
n
n
2
3
16]
II
group migration from M to Ni to yield an intermediate I
though CrCl also mediates a similar coupling reaction of
(R ˆ Et). This is followed by b-dehydronickelation and
2
alkyl iodides, 1,3-dienes, and carbonyl compounds, this
reaction displays contrasting regioselectivity: The alkyl and
carbonyl groups combine with 1,3-dienes at the C1 and C2
positions, respectively, to provide 2-alkylmethyl-3-buten-1-
[
*] Prof. Dr. Y. Tamaru, Dr. M. Kimura, S. Matsuo, K. Shibata
Department of Applied Chemistry
Faculty of Engineering, Nagasaki University
1-14 Bunkyo-machi, Nagasaki 852-8521 (Japan)
[17]
ols.
Fax: (‡81)958-47-9008
Intrigued by the synthetic possibilities and the facility with
which dimethylzinc, 1,3-butadiene, and benzaldehyde com-
bine with one another linearly in this sequence under very
E-mail: tamaru@net.nagasaki.u-ac.jp
[
**] We thank Y. Ohhama, NMR Facility, for technical assistance.
Financial support by the Ministry of Education, Science, Sports and
Culture, Japanese Government, is gratefully acknowledged.
0
mild conditions with catalysis by Ni in the absence of any
3
386
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Angew. Chem. Int. Ed. 1999, 38, No. 22

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Table 1. Nickel(0)-catalyzed coupling reaction of dimethylzinc, 1,3-dienes, and carbonyl compounds.[a]
tries 6 ± 10]. Isoprene selectively af-
fords the 1:1:1 adducts 4. In contrast to
1,3-butadiene, isoprene even reacts
with ketones to give 4 as the major
product (entry 10). All the products 4
are regiochemically homogeneous;
this indicates that isoprene selectively
reacts at C1 with carbonyl compounds
and at C4 with dimethylzinc. How-
ever, compounds 4 proved to be
mixtures of stereoisomers ((E)- and
(Z)-4 in a ratio of 2:1 ± 4:1). As is
apparent from H and C NMR spec-
tra, 5 consists of more than three
stereoisomers. However, close exami-
nation of three alcoholic fragments
derived from 5 by ozonolysis and
reduction of the reaction mixture with
Entry Carbonyl
compound
1,3-Diene
T [8C]/t [h]
Yield [%][b, c]
1:1:1 product[d]
1:2:1 product[e]
1
2
PhCHO
Ph
butadiene
butadiene
25 (2)
25 (1)
2a: 99
2b: 83
3a: 0
3b: 3
CHO
CHO
tBuCHO
3
4
5
butadiene
butadiene
butadiene
25 (1)
25 (3)
30 (3)
2c: 73
2d: 75
2e: 0
3c: 17
3d: 20
3e: 89
O
6
7
PhCHO
Ph
isoprene
isoprene
25 (5)
30 (1)
4a: 92 (E:Z ˆ 2.2:1)
4b: 40 (E:Z ˆ 3.8:1)
5a: 0
1
13
CHO
CHO
tBuCHO
5b: 10
8
9
0
isoprene
isoprene
isoprene
30 (1)
25 (3)
30 (3)
4c: 62 (E:Z ˆ 4.0:1)
4d: 57 (E:Z ˆ 2.4:1)
4e: 69 (E:Z ˆ 2.5:1)
5c: 11
5d: 8
O
1
5e: 10
NaBH revealed that 5 bears regio-
4
chemically homogeneous methyl
groups at the C3 and C8 positions
[Eq. (b)]; hence, isoprene molecules
selectively combined with each other
in a tail-to-tail manner.
[
(
a] A mixture of [Ni(acac)
2
](0.2 mmol), 1,3-butadiene or isoprene (8.0 mmol), an aldehyde or a ketone
2.0 mmol), and Me Zn (4.8 mmol, 1m in hexane) in dry THF (5 ml) was stirred at the indicated
2
temperature under N
2
[Eqs. (a), (b)]. [b] Yields refer to the isolated materials. All products were
1
13
characterized by H NMR (400 MHz), C NMR (100 MHz), and IR spectroscopy, high-resolution mass
spectrometry, and/or elemental analysis. [c] In addition to 2 ± 5, 1-methyl-3-phenylpropan-1-ol (15%,
entry 2), 1-cyclohexylethan-1-ol (10%, entry 3), 1-methyl-3-phenylpropan-1-ol (48%, entry 7), or
The reaction mechanism remains
speculative at present. One likely
scenario is outlined in Scheme 2. The
1
-cyclohexylethan-1-ol (20%, entry 8) was obtained. [d] The E:Z ratios are determined on the basis of
1
13
H and C NMR spectroscopy. [e] Compound 3 contains a small amount of an isomer (<10%),
1,3-butadiene ± nickel(0) complex may
phosphane ligands, we examined the scope of the present
reaction by varying the type of carbonyl compound (Table 1,
entries 1 ± 5). Dihydrocinnamaldehyde furnished the expect-
ed 2b in 83% yield; however, the unexpected product 3b (the
R
R'
R
R'
R
R'
a)
O
O
O
ZnMe
ZnMe
NiII
Ni0
Ni0
ZnMe2
Me
1
:2:1 coupling product of dimethylzinc, 1,3-butadiene, and the
aldehyde) was also obtained as a minor product in 3% yield
entry 2). Interestingly, the relative amount of 3 to 2 gradually
IV
Me III
II
2
4
(R = H)
(R = Me)
(
increased as the steric bulk around the carbonyl moiety
increased (entries 3 and 4). Indeed, acetone gave 3e as the
sole product (entry 5).
R
R
R'
R
R'
R
R
R'
b)
O
O
O
ZnMe
ZnMe
Ni0
NiII
Ni0
ZnMe2
The products 2 are regio- and stereochemically homoge-
neous; all possess the common structural features of (E)-3-
hexen-1-ol (see Experimental Section). The (E,E)-3,7-deca-
Me
Me
R
V
VI
VII
3 (R = H)
5 (R = Me)
[
18]
dien-1-ol structure of 3 was elucidated from spectroscopic
1
Scheme 2. Possible mechanism for the formation of 2/3 and 4/5.
data: In the H NMR spectrum (400 MHz, CDCl ) the olefin
3
proton signals (multiplets) separated into signals integrating
for 1H (dt, J ˆ 15.5, 6.0 Hz), 1H (dt, J ˆ 15.5, 6.0 Hz), and 2H
react with carbonyl compounds by path a to give the 1:1:1
(
m) in the presence of [Eu(fod) ] (fod ˆ 6,6,7,7,8,8,8-
3
adducts 2.[ An intermediate III (R ˆ H) with a syn-p-
20]
1
3
heptafluoro-2,2-dimethyl-3,5-octanedionato); the C NMR
[21]
allylnickel(ii) structure would undergo reductive elimina-
(
100 MHz, CDCl ) chemical shifts are in good agreement with
3
tion[ in such a way as to deliver the methyl group to the
22]
[
19]
the calculated values; and the IR spectrum contains a band
0
�
1
distal site, so that coordination of Ni with both Zn�O
at nÄ ˆ 970 cm (s).
(
nonbonding electron pair) and trans-CHˆCH is better
We next examined the reaction of isoprene with carbonyl
compounds under similar conditions [Eq. (b); Table 1, en-
[23]
maintained.
For less reactive carbonyl compounds, the
potential of II to undergo oxidative cyclization might be
insufficient to lead to III; hence, a small equilibrium concen-
tration of bis-butadiene ± nickel(0) complex V would then
lead to VI. In this case, V is assumed to display higher
reactivity than II owing to its greater polarizability (path b).
Isoprene might react selectively by path a, irrespective of the
type (reactivity) of carbonyl compound, since path b might be
O
0.1 [Ni(acac)2]
THF, 25–30 °C
(b)
Me2Zn
+
+
R
OH
OH
8
R
3
R
4
5
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unfavorable owing to steric congestion in V (R ˆ Me). A
higher electron density on C1 of isoprene than on C4 might
contribute to the selective nucleophilic C1 addition of
isoprene to carbonyl compounds.
R. J. Thomas, Tetrahedron Lett. 1995, 36, 4283 ± 4286; c) S. Kobayashi,
K. Nishino, J. Org. Chem. 1994, 59, 6620 ± 6628.
5] H. Miyake, K. Yamamura, Chem. Lett. 1992, 507 ± 508.
6] a) T. Ishiyama, M. Yamamoto, N. Miyaura, Chem. Commun. 1997,
[
[
6
89 ± 690; b) T. Ishiyama, M. Yamamoto, N. Miyaura, Chem.
Organozinc compounds with no accessible b-hydrogen
atoms can similarly undergo a three-component connection
reaction. For example, as illustrated in Equation (c), diphe-
nylzinc [1.2 mmol, from ZnCl2 (1.2 mmol) and PhMgBr
Commun. 1996, 2073 ± 2074.
7] M. Suginome, H. Nakamura, T. Matsuda, Y. Ito, J. Am. Chem. Soc.
[
[
1
998, 120, 4248 ± 4249.
8] S. Onozawa, Y. Hatanaka, M. Tanaka, Tetrahedron Lett. 1998, 39,
9043 ± 9046.
(
2.4 mmol)] reacted with 1,3-butadiene (4.0 mmol) and ben-
[9] Y. Obora, Y. Tsuji, T. Kawamura, J. Am. Chem. Soc. 1995, 117, 9814 ±
9821.
[10] Y. Obora, Y. Tsuji, T. Kawamura, Organometallics 1993, 12, 2853 ±
zaldehyde (1.0 mmol) to furnish (E)-1,5-diphenyl-3-penten-1-
[
24]
ol (6a) in 61% yield of isolated product. No 1:2:1 adducts
were detected, even for the reaction with pivalaldehyde, from
which 6b was isolated as the sole product [Eq. (c)].
2
856.
[
[
11] Y. Obora, Y. Tsuji, T. Kakehi, M. Kobayashi, Y. Shinkai, M. Ebihara,
T. Kawamura, J. Chem. Soc. Perkin Trans. 1 1995, 599 ± 608.
12] Wacker-type oxidative 1,4-difunctionalization: A. Aranyos, K. J.
Szabo, J.-E. Bäckvall, J. Org. Chem. 1998, 63, 2523 ± 2529.
[13] a) M. Kimura, H. Fujimatsu, A. Ezoe, K. Shibata, M. Shimizu, S.
Matsumoto, Y. Tamaru, Angew. Chem. 1999, 111, 410 ± 413; Angew.
Chem. Int. Ed. 1999, 38, 397 ± 400; b) M. Kimura, A. Ezoe, K. Shibata,
Y. Tamaru, J. Am. Chem. Soc. 1998, 120, 4033 ± 4034.
OH
O
0.1 [Ni(acac)2]
Ph2Zn
+
+
(c)
Ph
6
6
R
R
THF, 25 °C, 20 min
a: R = Ph, 61%
b: R = tBu, 70%
[14] Ni-catalyzed allylation of carbonyl compounds with 1,3-dienes: a) M.
Takimoto, Y. Hiraga, Y. Sato, M. Mori, Tetrahedron Lett. 1998, 39,
Experimental Section
4
543 ± 4546; b) Y. Sato, T. Takanashi, M. Hoshiba, M. Mori,
(
E)-1-phenyl-3-hexen-1-ol (2a): To a homogeneous solution of [Ni(acac)
2
]
Tetrahedron Lett. 1998, 39, 5579 ± 5582, and references therein; Ni-
promoted homoallylation of carbonyls with 1,3-dienes: c) Y. Sato, M.
Takimoto, M. Mori, Tetrahedron Lett. 1996, 37, 887 ± 890.
(
51.2 mg, 0.2 mmol) in dry THF (5 mL) were added 1,3-butadiene (670 mL,
8
1
.0 mmol), benzaldehyde (212 mg, 2.0 mmol), and dimethylzinc (4.8 mL,
m in hexane). The mixture was stirred at room temperature for 2 h under
[15] a) J. Seo, H. M. P. Chui, M. J. Heeg, J. Montgomery, J. Am. Chem. Soc.
1999, 121, 476 ± 477; b) M. V. Chevliakov, J. Montgomery, Angew.
Chem. 1998, 110, 3346 ± 3348; Angew. Chem. Int. Ed. 1998, 37, 3144 ±
3146; c) D.-M. Cui, H. Yamamoto, S.-I. Ikeda, K. Hatano, Y. Sato, J.
Org. Chem. 1998, 63, 2782 ± 2784; d) S.-I. Ikeda, N. Mori, Y. Sato, J.
Am. Chem. Soc. 1997, 119, 4779 ± 4780, and references therein.
[16] Three-component reaction of allylic Grignard reagents, isoprene, and
carbonyl compounds: F. Barbot, P. Miginiac, J. Organomet. Chem.
1978, 145, 269 ± 276.
[17] K. Takai, N. Matsukawa, A. Takahashi, T. Fujii, Angew. Chem. 1998,
110, 160 ± 163; Angew. Chem. Int. Ed. 1998, 37, 152 ± 155.
[18] The product 3 is contaminated with a chromatographically (recycle
HPLC) inseparable isomer (<10%), the structure of which is
tentatively assigned as C1-substituted (E)-7-methyl-3,8-nonadien-1-
ols.
N
2
and then quenched by adding 2m HCl (5 mL). The mixture was
extracted with ethyl acetate (2 Â 20 mL), and the organic extracts were
combined, washed with saturated NaHCO , dried over MgSO , and
3
4
concentrated in vacuo. The residue was purified by column chromatog-
raphy on silica gel with hexane/ethyl acetate (64/1) to give 1a in 99% yield.
R
f
ˆ 0.42 (hexane/ethyl acetate, 8/1); IR (neat): nÄ ˆ 3400 (s), 1500 (s), 1460
� 1 1
(
s), 1050 (s), 970 (s), 760 cm (s); H NMR (400 MHz, CDCl
3
, TMS): d ˆ
0
.98 (t, J ˆ 7.3 Hz, 3H), 1.86 (brs, 1H), 2.05 (brdq, J ˆ 6.2, 7.3 Hz, 2H), 2.39
(
(
(
1
m, 1H, coalesces to brdd, J ˆ 8.1, 13.9 Hz on irradiation at d ˆ 5.40), 2.47
m, 1H, coalesces to brdd, J ˆ 4.8, 13.9 Hz on irradiation at d ˆ 5.40), 4.68
dd, J ˆ 4.8, 8.1 Hz, 1H), 5.40 (ddm, J ˆ 6.2, 15.4 Hz, 1H), 5.63 (brdt, J ˆ
1
3
3
5.4, 6.2 Hz, 1H), 7.24 ± 7.29 (m, 5H); C NMR (100 MHz, CDCl , TMS):
d ˆ 13.7, 25.6, 42.7, 73.5, 124.5, 125.8, 127.3, 128.3, 136.6, 144.1; HR-MS calcd
‡
for C12
H
16O: 176.1201; found (%): 176.1195 (2) [M ], 107 (100), 77 (23), 69
(
3).
[19] Chemical shifts were calculated with the program CS ChemNMR Pro
(
CambridgeSoft Corpration, Cambridge, MA).
Received: May 17, 1999
Revised version: July 12, 1999 [Z13418IE]
German version: Angew. Chem. 1999, 111, 3586 ± 3589
[20] Relevant precedents that support the transformation of II into III,
that is, allylation of carbonyls by transition metal ± 1,3-diene com-
plexes at the C1 terminus: a) G. Erker, Angew. Chem. 1989, 101, 411 ±
4
26; Angew. Chem. Int. Ed. Engl. 1989, 28, 397 ± 412; b) G. Wilke,
Angew. Chem. 1988, 100, 189 ± 211; Angew. Chem. Int. Ed. Engl. 1988,
Keywords: aldehydes ´ homogeneous catalysis ´ multicom-
ponent reactions ´ nickel ´ zinc
2
7, 185 ± 206; c) H. Yasuda, A. Nakamura, Angew. Chem. 1987, 99,
7
45 ± 764; Angew. Chem. Int. Ed. Engl. 1987, 26, 723 ± 742. An
II
alternative mechanism which relies on the addition of MeNi to 1,3-
butadiene followed by the allylation of the carbonyl compounds by
the thus-formed 1-ethyl-p-allylnickel complex is less probable, since
1-ethyl-p-allylnickel is expected to selectively react with carbonyls at
C1 to give 2-ethyl-3-buten-1-ols: d) R. Baker, M. J. Crimmin, J. Chem.
Soc. Perkin Trans. 1 1979, 1264 ± 1267; e) S. Akutagawa, Bull. Chem.
Soc. Jpn. 1976, 49, 3646 ± 3648; see also: f) K. Ohno, T. Mitsuyasu, J.
Tsuji, Tetrahedron 1972, 28, 3705 ± 3720.
[
1] a) R. Benn, N. Büssemeier, S. Holle, P. W. Jolly, R. Mynott, I.
Tkatchenko, G. Wilke, J. Organomet. Chem. 1985, 279, 63 ± 86; b) G.
Wilke, B. Bogdanovic, P. Hardt, P. Heimbach, W. Keim, M. Kröner, W.
Oberkirch, K. Tanaka, E. Steinbrücke, D. Walter, H. Zimmermann,
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5
, 151 ± 164.
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77; b) J. M. Takacs, M. R. Jaber, A. V. Strakhov, R. V. Athalye,
[
[21] a) D. Walther, E. Dinjus, H. Görls, J. Sieler, O. Lindqvist, L. Andersen,
J. Organomet. Chem. 1985, 286, 103 ± 114; b) H. Hoberg, D. Schaeffer,
J. Organomet. Chem. 1983, 255, C15 ± C17.
[22] a) H. Schenkluhn, R. Berger, B. Pittel, M. Zähres, Transition Met.
Chem. (London) 1981, 6, 277 ± 287; b) H. Schenkluhn, H. Bandmann,
Transition Met. Chem. (London) 1981, 6, 287 ± 295.
[23] Chelation control of regioselectivity for Ni-catalyzed reactions:
a) C. N. Farthing, P. Kocovsky, J. Am. Chem. Soc. 1998, 120, 6661 ±
6662; b) M. T. Didiuk, J. P. Morken, A. H. Hoveyda, J. Am. Chem.
Soc. 1995, 117, 7273 ± 7274.
[24] Under similar conditions, bis(phenylethynyl)zinc reacted only with
benzaldehyde to provide 1,3-diphenyl-2-propyn-1-ol (98%).
8
Tetrahedron Lett. 1998, 39, 5003 ± 5006; c) J. M. Takacs, F. Clement, J.
Zhu, S. V. Chandramouli, X. Gong, J. Am. Chem. Soc. 1997, 119,
5804 ± 5817; d) M. Murakami, K. Itami, Y. Ito, J. Am. Chem. Soc. 1997,
119, 7163 ± 7164; e) M. Lautens, W. Klute, W. Tam, Chem. Rev. 1996,
96, 49 ± 92.
[
[
3] a) M. Zaidlewicz, J. Meller, Tetrahedron Lett. 1997, 38, 7279 ± 7282;
b) M. Satoh, Y. Nomoto, N. Miyaura, A. Suzuki, Tetrahedron Lett.
1989, 30, 3789 ± 3792.
4] a) K. Kitayama, H. Tsuji, Y. Uozumi, T. Hayashi, Tetrahedron Lett.
1996, 37, 4169 ± 4172; b) C. Bismara, R. D. Fabio, D. Donati, T. Rossi,
3
388
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1999
1433-7851/99/3822-3388 $ 17.50+.50/0
Angew. Chem. Int. Ed. 1999, 38, No. 22