Chemistry Reference
In-Depth Information
activate organosilicon compounds and the selective conversions of aryltrimethylsilanes
catalysed by
t
Bu-P4 base have been investigated [57].
The reaction of 1-trimethylsilylnaphthalenewith pivaldehyde in the presence of 20mol%
t
Bu-P4 base proceeded smoothly at room temperature to give the alcohol in 91% yield.
Other phosphazene bases withweaker basicities, such as
t
Bu-P2 base and BEMP, showed no
catalytic activity. As one of the conventional strong organic bases, DBU was found to be
inactive. Caesium fluoride (CsF) was then examined as a fluoride anion donor, but no
carbon-silicon bond cleavage was observed. Reactions with other aldehydes have been
examined; that with benzaldehyde was found to proceed somewhat slowly at room
temperature. Other aryl aldehydes with electron-donating groups were also employed as
electrophiles and the reactions proceeded smoothly at room temperature [57] (Table 5.5).
The reactions of other aryltrimethylsilanes have been examined. 2-Trimethylsilyl-
naphthalene reacted with pivalaldehyde in the presence of t-Bu-P4 base at room tempera-
ture to give the alcohol in 68% yield. 4-Fluorophenyltrimethylsilane and 4-bromophenyl-
trimethylsilane gave the corresponding alcohols in 64 and 73% yields respectively.
Similarly, 4-trifluoromethylphenyltrimethylsilane and 2-trifluoromethylphenyltrimethyl-
silane reacted smoothly to give the alcohols in 69 and 73% yields respectively.
4-Methoxycarbonylphenyltrimethylsilane reacted to give the alcohol in 46% yield. The
reactions of heteroaryltrimethylsilanes were then examined. 2-Pyridyltrimethylsilane and
3-pyridyltrimethylsilane reacted smoothly to give the alcohols in 67 and 80%. 2-Thienyl-
trimethylsilane also reacted to give the alcohol in 81% yield [57] (Table 5.6).
2-Trimethylsilylated benzamide was reacted with benzaldehyde to give the 1,2-adduct,
which was treated with AcOH-toluene to give the phthalide in 76% yield. Phthalides have
been used as precursors for the synthesis of anthraquinones [57] (Scheme 5.37).
5.3.2.4 Peterson Olefination
Condensation of
-silylalkyl compounds with carbonyl compounds to form alkenes has been
known as the Peterson olefination reaction. Usually an
a
a
-silanyl carbanion generated in situ
Table 5.5
Selective functionalization of arylsilane
HO
R
TMS
R-CHO
base (20 mol%)
DMF, temp., time
Temp. (
C)
Run
Base
R
Time (h)
Yield (%)
t
Bu-P4
t
Bu
1
rt
1
91
t
Bu-P2
t
Bu
2
rt
24
0
t
Bu
3
BEMP
rt
24
0
t
Bu
4
DBU
rt
24
0
t
Bu
5
CsF
rt
24
0
t
Bu-P4
6
Ph
80
6
61
t
Bu-P4
7
4-MeOC
6
H
4
rt
1
78
t
Bu-P4
8
2-MeOC
6
H
4
rt
1
68
