ca01 only detailed ToC 1..24

156 Science of Synthesis 4.4 Silicon Compounds
Scheme 13 Æ-Haloalkylsilanes in the Peterson Reaction [81,82]
Me3Si
R 1
Cl
MgCl
1. R 1 COR 2
2. H + /H2O
R
Me3Si 1
HO R2 38 39
SiMe2Ph
1. Mg, Et 2O
2. CuBr SMe 2
3. R 2 COCl
R 1
22 41
SiMe 2Ph
O
R 2
KH
1. R 3 M
2. KH
1. R 3 M
2. TsOH
The Grignard reagents of (chloroalkyl)(isopropoxy)dimethylsilane (42, R 1 = O-iPr) and
(chloroalkyl)(dimethyl)phenylsilane (43, R 1 = Ph) provide excellent hydroxyalkyl anion
equivalents, which react with electrophiles such as aldehydes, imines, [80] ketones and epoxides
to give the adducts 44 and 45, respectively (Scheme 14). The hydroxyalkyl group
46 is revealed using the standard silyl-to-hydroxy protocols.
Scheme 14 Hydroxymethylation with Æ-Haloalkylsilanes [80]
R 1 Me2Si Cl
R 2
42 R 1 = O-iPr; R 2 = alkyl
43 R 1 = Ph; R 2 = alkyl
1. Mg, THF
2. E +
R 1 Me2Si E
R 2
44 R 1 = O-iPr; R 2 = alkyl
45 R 1 = Ph; R 2 = alkyl
R 1
for 44: H2O2, F − , base
for 45: KBr, NaOAc
AcOOH
R 1
R 1
40
R 2
R 3
R 2
R 2
R 3
HO E
Æ-Haloalkylsilanes readily undergo halogen substitution (e.g., 47 fi 48) by a wide range of
nucleophiles such as iodide, [85] ammonia, azide, [86] amines, [87] diethyl phosphonacetate, [88]
and phosphorus ylides [89] (Scheme 15). The use of iodide and fluoride as nucleophiles provides
a useful method for the preparation of Æ-iodo- and Æ-fluoroalkylsilanes from Æ-bromo-
and Æ-chloroalkylsilanes. Fluoromethyl-substituted silanes are prepared in moderate
yield by the reaction of the corresponding chloromethyl compound with cesium fluoride
in the presence of 18-crown-6. [90] A variation of the substitution reaction is the nucleophile-induced
1,2-transfer of a group bound to the silicon atom (e.g., 49 fi 50), which
can interfere sometimes with the direct displacement (e.g., 47 fi 48).
Scheme 15 Halide Substitution in Æ-Haloalkylsilanes [85–90]
R 1 3Si Cl
R 2
47 R 2 = alkyl
R 1 3Si Cl
R 2
49 R 2 = alkyl
Nu −
Nu −
R 1 3Si Nu
48
R 2
NuR 1 2Si R 1
50
R 2
R2 46