Synthesis and reactivity of functionalized alkynyl titanium derivatives

Article abstract of DOI:10.1055/s-2000-6288

The in situ formation of Ti(II) and subsequent reaction with halogeno alkynes offer a new route to the preparation of functionalized alkynyl titanium derivatives, which can then react chemoselectively with functionalized electrophiles.

Full text of DOI:10.1055/s-2000-6288

PAPER
917
Synthesis and Reactivity of Functionalized Alkynyl Titanium Derivatives
Natalia Morlender-Vais, Julia Kaftanov, Ilan Marek*
Department of Chemistry and Institute of Catalysis Science and Technology, Technion-Israel Institute of Technology,Technion City, Haifa
2000 Israel
3
Fax (972)48233735; E-mail: chilanm@tx.technion.ac.il
Received 14 January 2000
Et2O
iPrO
iPrO
iPrO
iPrO
Abstract: The in situ formation of Ti(II) and subsequent reaction
with halogeno alkynes offer a new route to the preparation of func-
tionalized alkynyl titanium derivatives, which can then react
chemoselectively with functionalized electrophiles.
Ti(OiPr)4 + 2 iPrMgBr
Ti
Ti
1
Equation 1
Key words: titanium, functionalized organometallic, halogeno
alkynes, alkynes
In these intramolecular nucleophilic acyl substitution re-
actions, the nucleophile must be generated in the presence
of a carbonyl functional group, and at the same time this
nucleophile is expected to react only with the carbonyl
group in an intramolecular fashion but not intermolecular-
Most organic molecules are polyfunctional compounds1
requiring in the retrosynthetic analysis, the reaction be-
tween a functionalized carbon electrophile and a function-
alized carbon nucleophile. Although a large part of the
8
ly.
carbon nucleophiles are organometallic derivatives, the We have recently reported that treatment of 1-halo-
highly reactive nature of the carbon-metal bond precludes genoalkyne 2 (Scheme 2, R = alkyl, aryl X = I, Br, Cl,
i
the presence of functional groups in the carbon skeleton of SPh) with 2.5 equivalents of the combination Ti(O Pr)
/2
4
these reagents. Several elegant solutions to these prob- i-PrMgBr (Sato’s reagent as described in eq.1) gives, in a
lems were successfully developed in particular with the single-pot operation at -50 °C in 2 hours, the desired ti-
synthesis of functionalized nucleophiles as organozinc tano-titanacyclopropene
5
in high chemical yield
2
11
derivatives. On the other hand, organotitanium reagents (Scheme 2, path A).
undergo chemoselective and stereoselective carbon-car-
3
bon bond forming reactions with bifunctional electro-
R
X
philes as shown in Scheme 1 (>99% reaction on the
2
iPrMgBr
Et2O
4
X
+
Ti(OiPr)4
R
aldehyde).
2
Ti
-80°C
iPrO
OiPr
3
-80°C to
- 50°C
ClTi(OiPr)3
R
Li (MgBr)
R
Ti(OiPr)3
R
TiX(OiPr)2
Ti(II)
O
R
TiX(OiPr)2
Ti
Path A
1) Ph
4
O
H
iPrO
OiPr
5
O
E+ Path B
R
Ph
2
) H3O+
OH
R
E
Scheme 1
Scheme 2
However, as these transition-metal organometallics were
prepared from lithium or magnesium reagents, functional-
ized titanium organometallics are still in their infancy.3
Indeed, few examples are described in the literature;
mostly for the synthesis of trichloro- and alkoxytitanium
The postulated mechanism for this reaction is that the in
2
10
situ formed diisopropyloxy(h -propene) titanium 1
(
generated as described in Equation 1) reacts with halo-
genoalkyne 2, via a ligand exchange, to give the unstable
5
homoenolates. The recent chemistry based on Ti(II) de-
rivatives have shown a high tolerance for oxygenated
12
halogeno-titanacyclopropene 3 as intermediate. Then, 3
13
undergoes a very fast b-elimination at low temperature
functional groups as in the enyne cyclocarbonylation
to give the alkynyltitanium derivative 4, which reacts with
the second equivalent of 1 to give the titano-titanacyclo-
propene 5 (an alternative possible mechanism for the for-
mation of 4 is the oxidative addition of Ti(II) into the
carbon-chlorine bond of 2). Although the exact chemical
pathway for the transformation of 2 into 4 is ambiguous,
6
reaction involving “Cp Ti” (from Cp TiCl and 2 equiv-
2
2
2
7
alents of EtMgBr) or in the intramolecular nucleophilic
acyl substitution reactions [Ti(II) is prepared from
8
9
i
Ti(O Pr) and 2 equivalents of i-PrMgBr as described in
4
1
0
Equation 1].
Synthesis 2000, No. 7, 917–920 ISSN 0039-7881 © Thieme Stuttgart · New York

9
18
N. Morlender-Vais et al.
PAPER
Table Reactivity of the Alkynyl Titanium 4
described in Scheme 3. Thus, treatment of an ethereal
solution of functionalized chloroalkynes and Ti(O Pr)4
i
Entries
R
E
Pdt
Lewis Acid Yield(%)a
(
1.2 equivalents) with i-PrMgBr (2.4 equivalents) at -
1
2
3
4
Oct
MeOD
6
7
7
8
none
none
ClTi(OiPr)3 85
none 70
93
70
78 °C leads, by warming the reaction mixture up to -
50 °C, to the desired functionalized alkynyl titanium de-
rivatives in excellent yield. These derivatives tolerate a
large variety of functional groups on its carbon skeleton.
Halides like bromide or iodide (9 and 10 in 91% and 85%
yields respectively), tosylate 11 (81%), carbonate 12
pTolyl
pTolyl
pTolyl
iPrCHO
iPrCHO
PhCHO
a
Isolated yields after hydrolysis.
(
93%), ester 13 (87%) and b-keto ester 14 (68%) are com-
we would like to report here a general route to highly patible with the formation of the organometallic deriva-
functionalized alkynyltitanium derivatives of type 4. In- tives. They present a good reactivity with standard
deed, since Grignard reagents are relatively unreactive to- aldehyde even if, in some cases, the addition of Lewis acid
wards many functional groups at low temperature in is necessary in order to reach a good chemical yield. For
1
4
Et O, the transmetallation reaction between titanium tet- example, 12 was obtained only in 50% yield without ad-
2
i
raisopropoxide and i-PrMgBr to give 1 should be faster dition of ClTi(O Pr) , whereas it was formed in 70% yield
3
i
than the reaction of i-PrMgBr with other functional in the presence of a catalytic amount of ClTi(O Pr) (10%)
3
groups. Firstly, we have checked the reactivity of 4 with and in 93% when an equimolar amount of Lewis acid was
aldehydes on model compounds (R = alkyl or p-Tolyl, added.
X = Cl), Scheme 2 (path B) and Table.
Finally, the chemoselective reaction between a function-
Quenching the reaction with MeOD at -78 °C (Table, en- alized alkynyl titanium derivative and a functionalized
try 1) proved the presence of the metalated alkyne 4 since electrophile has been performed in order to prepare, in a
the deuterioalkyne 6 (R = Octyl, %D>95, 93%) was ob- one-pot procedure, a polyfunctional compound (Scheme
tained quantitatively. Addition of aldehydes to 4 led to the 4).
corresponding propargylic alcohols in good overall yields
entries 2, 3, 4). However, the co-addition of a mild Lewis
15
By applying the herein described strategy with Zr(II) in-
(
stead of Ti(II), we have also been able to prepare the cor-
responding functionalized alkynyl zirconium derivatives
in good yield.
In conclusion, the in situ formation of Ti(II)16 and subse-
quent reaction with halogeno alkynes offer a new route for
the preparation of functionalized alkynyl titanium deriva-
tives. These can further react chemoselectively with func-
i
acid as ClTi(O Pr) is beneficial for the reaction with an
3
aldehyde (Table, compare entries 2 and 3). Once the ex-
perimental conditions were set up on the model substrates
(
as described in Scheme 2 and Table), we focussed our at-
tention on the preparation of functionalized alkynes,
readily prepared from w-alkyn-1-ol, and their transforma-
tions into functionalized alkynyl titanium derivatives as
Br
OH
9
1%
I
9
i
OH
10
85%
i
TsO
i, ii
11 OH
81%
Ti(OiPr)4
FG
Cl
FG
TiCl(OiPr)2
n
n
2
iPrMgBr
Et2O
n = 1, 2
i, ii
O
O
Et
O
1
2
OH
i, ii
93%
i, ii
O
O
O
O
O
OH
1
4
13
87%
OH
68%
i
i) i-PrCHO (1 equiv), -50 °C to -30 °C; ii) ClTi(O Pr) (1 equiv), -50 °C.
3
Scheme 3
Synthesis 2000, No. 7, 917–920 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
Synthesis and Reactivity of Functionalized Alkynyl Titanium Derivatives
919
2
iPrMgBr
Et2O
6-Hydroxy-7-methyl-4-octynylethoxycarbonate (12); Typical
Procedure
I
Cl + Ti(OiPr)4
O
I
TiCl(OiPr)2
- 80°C to
50°C
To a stirred solution of the chloroacetylenic carbonate (216 mg,
-
i
1,13 mmol) and Ti(O Pr) (0.42 mL, 1.36 mmol) in Et O (25 mL)
1
) Ph
O
4
2
H
was added) dropwise i-PrMgBr (1.08 M in Et O, 2.5 mL, 2.7 mmol)
2
O
I
Ph
at -80 ºC. The reaction mixture was warmed to -50 ºC and kept
2
) H3O+
OH
i
1
5
at this temperature for 2 h. Ti(O Pr) Cl (2 M in Et O, 0.68 mL,
3
2
71%
1
.36 mmol) was introduced at -50 ºC and the mixture was stirred at
this temperature for 30 min. Freshly distilled isobutyraldehyde
0.16 mL, 1.7 mmol) was then added and the reaction mixture was
Scheme 4
(
stirred at -35 ºC for another 2 h. The reaction was quenched by ad-
dition of aq HCl (1 N, 20 mL) and extracted with Et O (3 × 20 mL).
2
tionalized electrophiles. This strategy can be easily
generalized to a large variety of alkynes since several mild
Combined organic phases were washed with sat. NaHCO , dried
3
(
MgSO ), and concentrated in vacuo. The crude product was puri-
4
methods are known for the transformation of alkynes into fied by flash chromatography (silica gel, hexane/EtOAc, 5:1) to af-
halogeno alkynes.1
7
ford the alcohol (240 mg, 93%) as a colorless oil.
1
H NMR (200 MHz): d = 0.92 (d, J = 6.8 Hz, 3H), 0.94 (d, J = 6.8
Hz, 3H), 1,28 (t, J = 7.8 Hz, 3H), 1.74-1.93 (m, 3H), 2.33 (dt,
J = 7.0, 1.8 Hz, 2H), 4.11-4.24 (m, 5H).
1H and 13C NMR spectra were recorded on AM Bruker 200 MHz
and 400 MHz spectrometers with CDCl as the solvent. All reac-
3
1
3
C NMR (50.3 MHz): d = 14.22, 15.31, 17.43, 18.04, 27.81, 34.61,
tions were carried out under an Ar atmosphere using flame-dried
6
3.94, 66.35, 68.03, 80.92, 84.31, 155.13.
glassware. THF and Et O were distilled, prior to use, from Na/ben-
2
i
zophenone ketyl. Ti(O Pr) was distilled and stored under Ar. Ben-
4
Anal: C H O (228.28): Calc C, 63.13; H, 8.83. Found: C, 63.21;
12 20 4
H, 8.92.
zaldehyde and isobutyraldehyde were distilled immediately prior to
i
i
use. Ti(O Pr) Cl was prepared from Ti(O Pr) and TiCl according
3
4
4
3
to the literature procedure. Flash column chromatography was car-
1
-Phenyl-3-p-tolyl-2-propyn-1-ol (8)
ried out on ICN Silica 63-200, 60Å.
The crude product was purified by flash chromatography (silica gel,
hexane/EtOAc, 5:1).
1
-Deuterio-1-decyne (6)
1
H NMR (200 MHz): d = 2.35 (s, 3H), 5.68 (s, 1H), 7.10 (d, J = 8.0
To a stirred solution of 1-chloro-1-decyne (166 mg, 0.96 mmol) and
i
Hz, 2H), 7.30-7.45 (m, 5H), 7.60 (d, J = 8.0 Hz, 2H).
Ti(O Pr) (0.31 mL, 1.06 mmol) in Et O (25 mL) was added drop-
4
2
1
3
wise i-PrMgBr (1 M in Et O, 2.1 mL, 2.12 mmol) at -80 ºC. The
C NMR (50.3 MHz): d = 31.39, 65.1, 86.81, 88.13, 119.4, 126.7,
2
mixture was warmed to -50 ºC and kept at this temperature for 2 h.
MeOD (0.78 mL, 20 mmol) was added and the mixture was allowed
to reach r.t. The reaction was quenched by addition of aq HCl (1 N,
128.3, 128.56, 129.01, 131.64, 138.69, 140.84.
8-Bromo-2-methyl-4-octyn-3-ol (9)
The crude product was purified by flash chromatography (silica gel,
hexane/EtOAc, 6:1).
2
0 mL) and extracted with Et O (3 × 20 mL). Combined organic
2
phases were washed with sat. NaHCO , dried (MgSO ) and concen-
3
4
trated in vacuo. The crude product was purified by flash chromatog-
raphy (silica gel, pentane) to afford the deuteriated product (124
mg, 93%, %D>95) as a colorless oil.
1
H NMR (200 MHz): d = 0.93 (d, J = 6.6 Hz, 3H), 0.95 (d, J = 6.6
Hz, 3H), 1.82 (m, 1H), 2.04 (q, 2H), 2.41 (dt, J = 6.7, 1.8 Hz, 2H),
3
.49 (t, J = 6.3 Hz, 2H), 4.14 (br d, J = 5.6 Hz, 1H).
1
H NMR (200 MHz): d = 0.88 (t, J = 6.7 Hz, 3H), 1.18-1.62 (m,
1
3
C NMR (50.3 MHz): d = 17.43, 18.07, 29.67, 31.48, 32.20, 34.63,
1
2H), 2.14 (t, J = 6.7 Hz, 2H).
6
8.06, 81.11, 83.88.
1
3
C NMR (50.3 MHz): d = 13.27, 17.57, 21.84, 27.71, 27.96, 28.26,
8.35, 31.02, 66.93, 83.49.
Anal: C H BrO (219.12): Calc C, 49.33; H, 6.90. Found: C, 49.44;
H, 6.98.
9
15
2
Anal: C H D (139.26): Calc C, 86.25; H, 12.30. Found: C, 86.41;
10
17
H, 12.61.
8
-Iodo-2-methyl-4-octyn-3-ol (10)
The crude product was purified by flash chromatography (silica gel,
hexane/EtOAc, 6:1).
2
-Methyl-5-p-tolyl-4-pentyn-3-ol (7)
To a stirred solution of 1-chloro-2-p-tolylacetylene (275 mg,
1
was added dropwise i-PrMgBr (1 M in Et O, 4.6 mL, 4.56 mmol) at
1
H NMR (200 MHz): d = 0.93 (d, J = 6.7 Hz, 3H), 0.95 (d, J = 6.7
i
.83 mmol) and Ti(O Pr) (0.68 mL, 2.28 mmol) in Et O (25 mL)
4 2
Hz, 3H), 1.82 (m, 1H), 1.96 (q, J = 6.6 Hz, 2H), 2.36 (dt, J = 6.6,
2
1
.8 Hz, 2H), 3.27 (t, J = 6.6 Hz, 2H), 4.14 (br d, J = 5.7 Hz, 1H).
-
80 ºC. The reaction mixture was warmed to -50 ºC and kept at this
temperature for 2 h. Freshly distilled isobutyraldehyde (0.25 mL,
.7 mmol) was then added and the reaction mixture was stirred at
30 ºC for another 2 h. The reaction was quenched by an addition
1
3
C NMR (50.3 MHz): d = 5.08, 17.46, 18.08, 29.67, 32.07, 34.64,
2
-
68.09, 81.18, 83.90.
Anal: C H IO (266.12): Calc C, 40.62; H, 5.68. Found: C, 41.2; H,
9
15
of aq HCl (1 N, 20 mL) and extracted with Et O (3 × 20 mL). Com-
2
5.96.
bined organic phases were washed with sat. NaHCO , dried
3
(
MgSO ), and concentrated in vacuo. The crude product was puri-
4
6
-Hydroxy-7-methyl-4-octynyl p-Toluenesulfonate (11)
fied by flash chromatography (silica gel, hexane/EtOAc, 6:1) to af-
ford the alcohol (240 mg, 85%) as a colorless oil.
The crude product was purified by flash chromatography (silica gel,
hexane/EtOAc, 5:1).
1
H NMR (200 MHz): d = 1.01 (d, J = 6.7 Hz, 3H), 1.04 (d, J = 6.7
1
H NMR (200 MHz): d = 0.89 (d, J = 5.2 Hz, 3H), 0.91 (d, J = 5.2
Hz, 3H), 1.93 (m, 1H), 2.32 (s, 3H), 4.35 (d, J = 5.5 Hz, 1H), 7.10
Hz, 3H), 1.66-1.88 (m, 3H), 2.33 (dt, J = 6.4, 1.8 Hz, 2H), 2.42 (s,
3
(
1
d, J = 8.1 Hz, 2H), 7.29 (d, J = 8.1 Hz, 2H).
H), 4.06 (br d, J = 5.8 Hz, 1H), 4.10 (t, J = 6.5 Hz, 2H), 7.32 (d,
3
C NMR (50.3 MHz): d = 17.51, 18.13, 21.35, 36.69, 68.37, 85.64,
J = 8.1 Hz, 2H), 7.77 (d, J = 8.1 Hz, 2H).
8
8.21, 119.65, 128.96, 131.55, 138.35.
Synthesis 2000, No. 7, 917–920 ISSN 0039-7881 © Thieme Stuttgart · New York

9
20
N. Morlender-Vais et al.
PAPER
(3) For a recent review, see: Reetz, M. In Organometallics in
1
3
C NMR (50.3 MHz): d = 14.98, 17.40, 17.99, 27.92, 29.64, 34.50,
6
7.92, 68.88, 81.26, 83.60, 127.87, 129.82, 133.10, 144.75.
Synthesis; Schlosser, M., Ed.; Wiley: 1994; p 195.
(
4) Krause, N.; Seebach. D. Chem. Ber. 1987, 120, 1845.
7
-Hydroxy-8-methyl-5-nonynyl Acetate (13)
(5) Kuwajima, I.; Nakamura, E. In Metal Homoenolates In
Comprehensive Organic Synthesis; Trost, B. M.; Fleming, I.,
Eds.; Pergamon: 1991; 2, p 441.
The crude product was purified by flash chromatography (silica gel,
hexane/EtOAc, 5:1).
(
6) Hicks, F. A.; Kablaoui, N. M.; Buchwald, S.L. J. Am. Chem.
Soc. 1999, 121, 5881.
1
H NMR (200 MHz): d = 0.93 (d, J = 6.7 Hz, 3H), 0.97 (d, J = 6.7
Hz, 3H), 1,52-1.85 (m, 5H), 2.03 (s, 3H), 2.25 (dt, J = 6.8, 1.9 Hz,
2
Grossman, R. B.; Buchwald, S. L. J. Org. Chem. 1992, 57,
H), 4.07 (t, J = 6.2 Hz, 2H), 4.14 (br d, J = 5.6 Hz, 1H).
5803.
1
3
C NMR (50.3 MHz): d = 17.43, 18.05, 18.34, 20.90, 25.1, 27.77,
4.66, 63.94, 68.11, 99.83, 104.63, 190.43.
(7) Buchwald, S. L.; Nielsen R. B. Chem. Rev. 1988, 88, 1047.
(8) Okamoto, S.; Iwakubo, M.; Kobayashi, K.; Sato, F. J. Am.
Chem. Soc. 1997, 119, 6984.
3
Anal: C H O (212.28): Calc C, 67.89; H, 9.50. Found: C, 68.03;
H, 9.84.
1
2
20
3
Urabe H.; Suzuki, K.; Sato, F. J. Am. Chem. Soc. 1997, 119,
1
0014.
Urabe, H.; Hamada, T.; Sato, F. J. Am. Chem. Soc. 1999, 121,
931.
2
-Methyl-2(8-methyl-5-nonyn-7-ol)ethyl Acetoacetate (14)
2
The crude product was purified by flash chromatography (silica gel,
hexane/EtOAc, 5:1).
Okamoto, S.; Kasatkin, A.; Zubaidha, P. K.; Sato, F. J. Am.
Chem. Soc. 1996, 118, 2208.
1
H NMR (400 MHz): d = 0.92 (d, J = 6.7 Hz, 3H), 0.95 (d, J = 6.7
(9) Kulinkovich, O. G.; Sviridov, S. V.; Vasilevski, T. S.;.
Pritskaya, T. S. Zh. Org. Khim. 1989, 25, 2245.
Kulinkovich, O. G; Pritskaya, T. S. J. Org. Chem. USSR
Hz, 3H), 1.23 (t, J = 7.4 Hz, 3H), 1.21-1.27 (m, 2H), 1.30 (s, 3H),
1
2
.49 (m, 2H), 1.67-1.88 (m, 3H), 2.11 (s, 3H), 2.2 (br t, J = 6.3 Hz,
H), 4.11 (br d, J = 5.4 Hz, 1H), 4.17 (q, J = 6.5 Hz, 2H).
(
Engl. Transl.) 1990, 25, 2027.
1
3
Kulinkovitch, O. G.; Sviridov, S. V.; Vasilevski, D. A.
Synthesis 1991, 234, and references cited therein.
Williams, C. M.; Chaplinski, V.; Schreiner, P. R.; de Meijere,
A. Tetrahedron Lett. 1998, 39, 7695.
C NMR (100.6 MHz): d = 14.06, 17.46, 18.11, 18.35, 18.83,
3.36, 26.12, 28.89, 34.25, 34.67, 59.61, 61.27, 68.10, 80.40, 85.54,
72.96, 205.49.
2
1
Anal: C H O (296.39): Calc C, 68.88; H, 9.52. Found: C, 68.97;
H, 9.71.
1
7
28
4
(
10) Harada, K.; Urabe, H.; Sato, F. Tetrahedron Lett. 1995, 36,
3203.
(
(
11) Averbuj, C.; Kaftanov, J.; Marek, I. Synlett 1999, 1939.
12) All attempts to trap the intermediate 3 at low temperature were
unsuccessful.
13) Equivalent reactions were described in the literature for the
formation of vinylzirconium derivatives from zirconocenes
and vinyl halides, see: Takahashi, T.; Kotora, M.; Fischer, R.;
Nishihara, Y.; Nakajima, K. J. Am. Chem. Soc. 1995, 117,
6
-Hydroxy-11-iodo-1-phenyl-7-undecyn-1-one (15)
The crude product was purified by flash chromatography (silica gel,
hexane/EtOAc, 6:1).
(
1
H NMR (200 MHz): d = 1.60-1.77 (m, 6H), 1.96 (q, J = 7.0 Hz,
2
H), 2.34 (br t, J = 6.8 Hz, 2H), 2.99 (t, J = 7.3 Hz, 2H), 3.26 (t,
J = 7.2 Hz, 2H), 4.48 (br t, J = 6.5 Hz, 1H), 7.44 (m, 3H), 7.92 (d,
J = 8 Hz, 2H).
11039.
(14) Boymond, L.; Rottlander, M.; Cahiez, G.; Knochel, P. Angew.
Chem., Int. Ed. 1998, 37, 1701.
1
3
C NMR (50.3 MHz): d = 5.12, 19.77, 24.95, 29.35, 31.44, 37.78,
8.42, 62.47, 82.42, 83.22, 128.02, 128.53, 132.90, 137.06, 200.09.
3
(
15) For the use of dialkylzirconocenes in synthesis, see the last
review: Neghishi, E. I.; Takahashi T. Bull. Chem. Soc. Jpn.
1998, 71, 755.
Anal: C H IO (384.24): Calc C, 53.13; H, 5.51. Found: C, 53.48;
H, 5.32.
17
21
2
(
16) Okamoto, S.; Kasatkin, A.; Zubaidha, P. K.; Sato, F. J. Am.
Chem. Soc. 1996, 118, 2208.
Acknowledgement
Hamada, T.; Suzuki, D.; Urabe, H.; Sato, F. J. Am. Chem. Soc.
1
999, 121, 7342.
I. M. is Holder of the Lawrence G. Horowitz Career Development
Chair, is a Ygal Alon fellow and Evelyn and Salman Grand Acade-
mic Lectureship-USA. This research was supported in part by The
Israel Science Foundation founded by The Academy of Sciences
and Humanities (N° 060-471) and by Technion V.R.P. Fund- S. and
N. Grand Research Fund. Acknowledgement is also made to the do-
nors of The Petroleum Research Fund, administered by the ACS,
for partial support of this research (PRF#33747-AC1). We also
thank the ministry of Immigrant Absorption for financial support.
Frid, M.; Perez, D.; Peat, A. J.; Buchwald, S. L. J. Am. Chem.
Soc. 1999, 121, 9469.
(
17) Wagner, A.; Heitz, M. P.; Mioskowski, C. Tetrahedron Lett.
1990, 31, 3141.
Naskar, D.; Roy, S. J. Org. Chem. 1999, 64, 6896.
Grandjean, D.; Pale, P.; Chuche, J. Tetrahedron Lett. 1994,
35, 3529.
Kloster-Jenson, E. Tetrahedron 1971, 27, 33.
Nishikawa, T.; Shibuya, S.; Hosokawa, S.; Isobe, M. Synlett
1994, 485.
References
(
1) Corey, E. J.; Cheng, X. The Logic of Chemical Synthesis;
Wiley: New-York, 1989.
2) For a recent review, see: Knochel, P. In Metal-Catalyzed
Cross-Coupling Reactions; Diederich, F.; Stang, P. J., Eds.;
Wiley-VCH, 1998; p 387.
Article Identifier:
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Synthesis 2000, No. 7, 917–920 ISSN 0039-7881 © Thieme Stuttgart · New York