SCHEME 4. Reactions of 1a with Arylzinc Reagents
mixture was quenched with an ice-cold saturated aqueous solution
of NH4Cl (300 mL). The organic compounds were extracted with
ethyl acetate three times (3 × 100 mL). The combined organic
part was washed with brine (100 mL). Then the organic part was
dried over Na2SO4 and concentrated in vacuo. After evaporation,
the residue was distilled to give (chloromethyl)dimethylphenylsilane
(3e, 74.0 g, 400 mmol, bp 105 °C at 19 mmHg) in 80% yield.
Procedure for the Synthesis of o-Chlorophenylphenylmethyl-
silane. o-Chloroiodobenzene (179 mg, 0.75 mmol) was placed in a
20-mL reaction flask under argon and dissolved in DME (1 mL).
i
The flask was cooled to -20 °C. PrMgCl·LiCl (1.0 M THF
solution, 0.80 mL, 0.80 mmol) was introduced dropwise to the flask.
The reaction mixture was stirred for 1 h at -20 °C. ZnCl2 ·TMEDA
(1.3 mg, 0.005 mmol) and chloromethylphenylsilane (1h, 78.3 mg,
0.50 mmol) were sequentially added at the same temperature. The
mixture was stirred for 8 h at -20 °C. The mixture was allowed to
warm slowly to 20 °C and stirred for 12 h at the same temperature.
A saturated aqueous solution of NH4Cl (2 mL) was then added.
The organic compounds were extracted with ethyl acetate three
times. The combined organic part was dried over Na2SO4 and
concentrated in vacuo. Purification by silica gel column chroma-
tography with hexane as an eluent afforded o-chlorophenylmeth-
ylphenylsilane (3j, 97.4 mg, 0.42 mmol) in 83% yield.
Characterization Data of Products. Products 3a-g,3 4a,13 4c,14
and 4d15 are known compounds and showed the identical spectra
according to the literature.
SCHEME 5. A Plausible Mechanism
(p-Cyanophenyl)dimethyl(p-methylphenyl)silane (3i): oil; IR
(neat) 2959, 2230, 1599, 1385, 1109, 818 cm-1; 1H NMR (CDCl3)
δ 0.56 (s, 6H), 2.36 (s, 3H), 7.18-7.21 (m, 2H), 7.37-7.40 (m,
2H), 7.59 (s, 4H); 13C NMR (CDCl3) δ -2.52, 21.66, 112.73,
119.18, 129.07, 131.15, 132.91, 134.30, 134.74, 139.81, 145.85;
HRMS found 251.1127 (∆ ) -1.4 ppm), calcd for C16H17NSi
251.1130.
was obtained in 72% yield (Scheme 4). Hence, the active species
of this reaction would be a zincate, (p-MeC6H4)3ZnMgX (X )
Cl or Br).12
Scheme 5 illustrates a plausible reaction mechanism. Trior-
ganozincate is initially generated from zinc chloride and 3 equiv
of a Grignard reagent. The zincate effects smooth organic group
transfer to afford the corresponding silane with concomitant
formation of diorganozinc. The initial triorganozincate is
regenerated by the reaction of diorganozinc with the remaining
Grignard reagent. The exact role of TMEDA is not clear at this
stage.
In summary, we report the zinc-catalyzed nucleophilic
substitution reaction of chlorosilanes with organomagnesium
reagents. The reaction described here provides a mild and
efficient method for the preparation of tetraorganosilanes.
o-Chlorophenylmethylphenylsilane (3j): oil; IR (neat) 3052,
1
2139, 1581, 1428, 1252 cm-1; H NMR (CDCl3) δ 0.70 (d, J )
3.9 Hz, 3H), 5.05 (q, J ) 3.9 Hz, 1H), 7.19-7.42 (m, 7H),
7.57-7.60 (m, 2H); 13C NMR (CDCl3) δ -4.95, 126.30, 128.15,
129.26, 129.81, 131.49, 134.54, 135.14, 135.27, 137.41, 141.48.
Anal. Calcd for C13H13ClSi: C, 67.08; H, 5.63. Found: C, 67.09;
H, 5.77.
Methyldiphenylvinylsilane (4b): oil; IR (neat) 3069, 1593, 1428,
1251, 1113 cm-1; 1H NMR (CDCl3) δ 0.63 (s, 3H), 5.78 (dd, J )
3.9, 20.1 Hz, 1H), 6.19 (dd, J ) 3.9, 14.4 Hz, 1H), 6.47 (dd, J )
14.4, 20.1 Hz, 1H), 7.36-7.37 (m, 6H), 7.50-7.54 (m, 4H); 13C
NMR (CDCl3) δ -3.96, 128.02, 129.49, 135.01, 135.11, 135.99,
136.41. Anal. Calcd for C15H16Si: C, 80.30; H, 7.19. Found: C,
80.54; H, 7.20.
Allyl(tert-butyl)dimethylsilane (4f): oil; IR (neat) 2929, 1632,
1472, 1252, 893 cm-1; 1H NMR (CDCl3) δ -0.05 (s, 6H), 0.89 (s,
9H), 1.53 (d, J ) 8.1 Hz, 2H), 4.79-4.88 (m, 2H), 5.73-5.87 (m,
1H); 13C NMR (CDCl3) δ -6.44, 16.95, 20.85, 26.74, 112.85,
135.90. Anal. Calcd for C9H20Si: C, 69.14; H, 12.89. Found: C,
69.05; H, 13.06.
Experimental Section
Typical Procedure for Zinc-Catalyzed Reactions. The reaction
of 1a with p-methylphenylmagnesium bromide (Table 1, entry 8)
is representative. ZnCl2 ·TMEDA (1.3 mg, 0.005 mmol) was placed
in a 20-mL reaction flask under argon. Chlorodimethylphenylsilane
(85 mg, 0.50 mmol) in 1,4-dioxane (1 mL) was added to the flask.
Then, p-methylphenylmagnesium bromide (1.0 M THF solution,
0.75 mL, 0.75 mmol) was added. The mixture was stirred at 20 °C
for 1 h. A saturated aqueous solution of NH4Cl (2 mL) was added.
The organic compounds were extracted with ethyl acetate three
times. The combined organic part was dried over Na2SO4 and
concentrated in vacuo. Chromatographic purification on silica gel
by using hexane as an eluent afforded dimethyl(p-methylphe-
nyl)phenylsilane (3a, 95.2 mg, 0.42 mmol) in 84% yield.
Procedure for Large-Scale Reaction (Scheme 1, Eq 2).
ZnCl2 ·TMEDA (1.26 g, 5 mmol) was placed in a 2-L reaction flask
under argon. Chloro(chloromethyl)dimethylsilane (71.5 g, 500
mmol) in 1,4-dioxane (500 mL) was added to the flask. The flask
was cooled to 0 °C. Phenylmagnesium bromide (1.2 M THF
solution, 500 mL, 600 mmol) was subsequently added over 20 min.
After the completion of the addition, the mixture was warmed to
20 °C and stirred at the same temperature for 3 h. The reaction
Acknowledgment. This work was supported by Grants-in-
Aid for Scientific Research and for GCOE Research from
MEXT and JSPS.
Supporting Information Available: . Characterization data.
This material is available free of charge via the Internet at
JO802433T
(13) Fleming, I.; Rowley, M.; Cuadrado, P.; Gonza´lez-Nogal, A. M.; Pulido,
F. J. Tetrahedron 1989, 45, 413–424.
(14) Huckins, J. R.; Rychnovsky, S. D. J. Org. Chem. 2003, 68, 10135–
10145.
(15) Commercially available.
J. Org. Chem. Vol. 74, No. 3, 2009 1417