Preparation of silyl-substituted dizinciomethanes and their reactions with electrophiles

Article abstract of DOI:10.1055/s-1998-1977

Silyl-substituted bis(bromozincio)methanes (RMe₂Si-CH(ZnBr)₂; R = Me, Ph, and p-MeO-C₆H₄), prepared from the corresponding dibromides by Pb catalyzed reaction with zinc, reacted stepwise with two different electrophiles, R¹X and E⁺, yielding R^1- CH(SiMe₂R)-E.

Full text of DOI:10.1055/s-1998-1977

December 1998
SYNLETT
1315
Preparation of Silyl-substituted Dizinciomethanes and Their Reactions with Electrophiles
Seijiro Matsubara,* Yasuyuki Otake, Takuya Morikawa, and Kiitiro Utimoto
Department of Material Chemistry, Graduate School of Engineering, Kyoto University, Yoshida, Sakyo, Kyoto 606-8501, Japan
Fax: 75-753-4863; E-mail: matsubara@orgrx2.kuic.kyoto-u.ac.jp
Received 25 August 1998
Abstract: Silyl-substituted bis(bromozincio)methanes (RMe Si-
was required for the second step reaction. The use of organocopper
species gave the way.
2
CH(ZnBr) ; R = Me, Ph, and p-MeO-C H ), prepared from the
2
6 4
corresponding dibromides by Pb catalyzed reaction with zinc, reacted
1
+
1–
stepwise with two different electrophiles, R X and E , yielding R
CH(SiMe R)–E.
2
gem-Dimetallic reagents have attracted considerable attention as
1
versatile reagents in organic synthesis. Among various combinations of
metals involved in the reagents, gem-dizincio reagents showed high
2,3
reactivity. The silyl substituted ones were expected to possess high
4,5
potential, but have not been prepared. The zinc reagent would be
Scheme 3
applied for the vinyl silane synthesis from carbonyl compounds via
2c,6,7
2a
olefination
and also for the sequential coupling reaction with the
two kinds of organic halides.
The sequential use of palladium catalyst and copper salt also made the
following transformations possible as shown in Table 1. A solution of
organozinc species 6 in THF, prepared from an organic halide and 2 in
the presence of Pd(0) catalyst 3, was treated with CuCN•2LiCl followed
We had reported the preparation of bis(iodozincio)methane from
diiodomethane and zinc dust in the presence of catalytic amount of
8
lead. Analogously RMe SiCHBr (1a: R = Me; 1b: R = Ph; 1c: R = p-
2
2
11
MeO-C H ) was treated with zinc dust in the presence of a catalytic
by the reaction with various organic halides. The homolallyl zinc
6
4
amount of lead in THF. The reaction temperature was crucial; at 60 °C,
species 6a prepared from cinnamyl chloride was reacted with allyl
bromide after a treatment with CuCN•2LiCl to give the coupling
product 8a in 88% yield (entry 1). It is the sharp contrast with the result
of Scheme 3. The use of propargyl bromide instead of allyl bromide
afforded the corresponding allene derivative (entries 4 and 5). The zinc
species prepared from iodobenzene and propargyl bromide by the Pd
catalyzed reaction with 2 as described above reacted with allyl bromide
via organocopper species (entries 6-9).
the corresponding dizincio compounds (2a-c) were obtained in 72–80%
9
yields (Scheme 1).
4
As organosilyl group can be oxidized into hydroxyl group, silyl-
Scheme 1
substituted dizinciomethanes described above can be used as
hydroxymethyl dianion equivalent. The oxidation detailed methods are
under investigation.
A coupling reaction with an organic halide under influence of transition
metal compounds were examined.
2a,b
As shown in Scheme 2, a reaction
of 2 with (E)-bromostyrene using Pd catalyst 3 at 25 °C gave organozinc
4; this compound reacted with allyl bromide, which was added
sequentially into the reaction mixture, to give 5a-c in 64–73% overall
yields. Thus two kinds of organic halides were connected with silyl-
substituted methylene group (Scheme 2).
Experimental Procedure:
10
Preparation of bis(bromozincio)trimethylsilylmethane (2a):
A mixture of Zn (4.9 g, 75 mmol) with catalytic amount of PbCl
2
(0.02 g) and 1a (0.74 g, 3 mmol) in 3.0 ml of THF was sonicated for 2 h
at 25°C. To the mixture THF (30 ml) and 1a (6.7 g, 27 mmol) were
added, then the mixture was stirred at 60 °C for 4 h affording 2a in 72%
yield.
Reaction of 2a with bromostyrene:
Bromostyrene (0.18 g, 1.0 mmol) was added to a THF solution (10 ml)
containing Pd dba •CHCl
3
(26 mg, 0.025 mmol) and
2
3
tris[3,5(trifluoromethyl)phenyl]phosphine (67 mg, 0.15 mmol), then the
mixture was stirred for 5 min. To the reaction mixture, 2a (0.7 M in
THF, 1.4 ml, 1.0 mmol) was added. The mixture was stirred for 2 h.
1
Yield of 4a was measured by H NMR spectroscopy using 2,2,3,3-
10
Scheme 2
tetramethylbutane as an internal standard. To the obtained THF
solution of 4a, allyl bromide (0.13 g, 1.1 mmol) was added and the
resultant solution was stirred for 6 h. Aqueous workup, extraction with
hexane-ethyl acetate, wash with brine, concentration, and purification
by column chromatography of the reaction mixture afforded 5a (0.17 g)
in 73% yield.
Reaction of 2a with allyl halides gave mono-adduct 6a in good yields,
but the sequential addition of allyl bromide afforded
trimethylsilylbutadienes 7 by β-elimination (Scheme 3). The reaction
may proceed via transmetalation of 6a to palladium(II) species; the
reductive elimination would form 7 with forming Pd(0) species which
are oxidized into Pd(II) species again by allyl bromide. An improvement
1
5a: H NMR (CDCl , 20 °C); δ 0.04 (s, 9H), 1.79 (dt, J = 4.2, 9.6 Hz,
3
1H), 2.1-2.4 (m, 2H), 4.93 (dt, J = 0.9, 9.0 Hz, 1H), 5.00 (dt, J = 1.5,

1316
LETTERS
SYNLETT
0 °C. Aqueous workup, extraction with hexane-ethyl acetate, wash with
brine, concentration, and purification by column chromatography of the
reaction mixture afforded 8a (0.24 g) in 88% yield.
1
6a: H NMR (THF-d , 20 °C); δ -0.11 (s, 9H), 2.37-2.51 (m, 2H), 6.16
8
(d, J = 15.9 Hz, 1H), 6.28 (d, J = 15.9, 6.9 Hz, 1H), 6.93-7.19 (m, 5H).
1
8a: H-NMR (CDCl , 20 °C); δ 0.03 (s, 9H), 0.87 (tt, J = 5.7, 7.8 Hz,
3
1H), 2.1-2.38 (m, 4H), 4.97-5.09 (m, 2H), 5.80 (ddt, J = 17.4, 10.2, 6.9
Hz, 1H), 6.18 (dt, J = 15.9, 6.9 Hz, 1H), 6.36 (d, J = 15.9 Hz, 1H), 7.1-
13
7.4 (m, 5H); C NMR (CDCl , 20 °C); δ -2.1, 26.1, 32.9, 33.8, 115.2,
3
126.0, 126.8, 128.6, 130.5, 131.1, 137.9, 139.1.
Acknowledgement. Financial support from the Ministry of Education,
Science, Sports and Culture, Japan (No. 10125217, 10132227) are
acknowledged.
References and Notes
(1) Marek, I.; Normant, J.-F. Chem. Rev. 1996, 96, 3241.
(2) (a) Utimoto, K.; Toda, N.; Mizuno, T.; Kobata, M.; Matsubara, S.
Angew. Chem. Int. Ed. Engl. 1997, 36, 2804. (b) Matsubara, S.;
Kawamoto, K.; Utimoto, K. Synlett 1998, 267. (c) Matsubara, S.;
Sugihara, M.; Utimoto, K. Synlett 1998, 313.
(3) Knochel, P.; Normant, J.-F. Tetrahedron Lett. 1986, 27, 4427,
4431; Nakamura, E.; Kubota, K.; Sakata, G. J. Am. Chem. Soc.,
1997, 119, 5457.
(4) Oxidation of C-Si bond into C-O bond: Colvin, E. W. In
Comprehensive Organic Synthesis, Vol. 7; Ley, S.V.; Trost, B. M.;
Fleming, I. Eds.; Pergamon Press: Oxford, 1991, p641.
(5) gem-Dimagnesium derivatives: Bertini, F.; Grasselli, P.; Zubiani,
G.; Cainelli, G. Tetrahedron 1970, 26, 1281; van de Heisteeg, B. J.
J.; Schat, G.; Tinga, M. A. G. M.; Akkerman, O. S.; Bickelhaupt,
F. Tetrahedron Lett. 1986, 27, 6123.
(6) Okazoe, T.; Takai, K.; Oshima, K.; Utimoto, K. J. Org. Soc. 1987,
52, 4410; Takai, K.; Kataoka, Y.; Miyai, J.; Okazoe, T.; Oshima,
K.; Utimoto, K. Org. Synth. 1996, 73, 73; Lombardo, L. Org.
Synth. 1987, 65, 81.
(7) Takai, K.; Kataoka, Y.; Okazoe, T.; Utimoto, K. Tetrahedron Lett.
1987, 28, 1443.
17.1 Hz, 1H), 5.83 (ddt, J = 17.4, 9.0, 6.9 Hz, 1H), 6.10 (dd, J = 15.9,
9.6 Hz, 1H), 6.23 (d, J = 15.9 Hz, 1H), 7.1- 7.4 (m, 5H); C NMR
13
(8) Bis(iodozincio)methane was prepared by the reaction of
diiodomethane with Zn under Pb catalysis; Takai, K.; Kakiuchi,
T.; Kataoka, Y.; Utimoto, K. J. Org. Chem. 1994, 59, 2668.
(CDCl , 20 °C); δ -3.1, 33.4, 34.1, 114.7, 125.7, 126.4, 127.6, 128.5,
3
132.5, 138.4, 139.1.
Reaction of 2a with cinnamyl chloride:
1
(9) Yield was determined by H NMR measurement using 2,2,3,3-
Cinnamyl chloride (0.15 g, 1.0 mmol) was added to a THF solution (10
tetramethylbutane as an internal standard. Reaction temperature is
crucial to obtain 2 in good yield; for example 2a, 72 % at 60 °C,
whereas 30% at 25 °C with contamination of
ml) containing Pd dba •CHCl (26 mg, 0.025 mmol) and
2
3
3
tris[3,5(trifluoromethyl)phenyl]phosphine (67 mg, 0.15 mmol), then the
mixture was stirred for 5 min. To the reaction mixture, 2a (0.7 M in
THF, 1.4 ml, 1.0 mmol) was added and the solution was stirred for 1 h.
1
bromo(bromozincio)trimethyl-silylmethane (40%). H NMR of
2a (THF-d at –63 °C): δ –1.62 (s, 1H), –0.09 (s, 9H).
8
1
Yield of homoallylzinc species 6a was measured by H NMR
1
(10) 4a: H NMR (THF-d , 20 °C); δ 0.05 (s, 9H), 1.52 (d, J = 12.9
8
spectroscopy. To a THF solution of 6a, a mixture of CuCN (90 mg, 1.0
mmol) and LiCl (85 mg, 2. 0 mmol) in THF (3 ml) was added at -30 °C.
The mixture was stirred for 15 min at the same temperature. Allyl
bromide (0.13 g, 1.1 mmol) was added and the resulting solution was
stirred for 1 h. During the stirring, the reaction temperature was raised to
Hz, 1H), 5.94 (d, J = 15.0 Hz, 1H), 6.66 (dd, J = 15.0, 12.9 Hz,
1H), 6.87-7.37 (m, 5H).
(11) Knochel, P.; Singer, R. D. Chem. Rev., 1993, 93, 2117; Knochel, P.
Synlett 1995, 393.