Chemistry Reference
In-Depth Information
Table 5.6
Transformation of functionalized arylsilane
t
BuCHO,
t
Bu-P4 (20 mol%)
OH
t
Bu
Ar
Ar-TMS
DMF, rt., time
Run
Ar
Time (h)
Yield (%)
1
2-Naphthyl
3
68
2
4-FC
6
H
4
1
64
3
4-BrC
6
H
4
1
73
4
4-CF
3
C
6
H
4
2
69
5
2-CF
3
C
6
H
4
1
73
6
4-MeOOCC
6
H
4
1
46
7
2-Pyridyl
1
67
8
3-Pyridyl
1
80
9
2-Thienyl
1
81
using a stoichiometric metallic base such as LDA has been used for the reaction. The reaction
has beenwidely employed as an importantmethod for alkene synthesis, because of the simpler
workup and purification procedure than the Wittig reaction. This condensation reaction is
considered tobemorevaluable if the transformationcanbeaccomplishedwithacatalyticbase.
When the reaction of benzophenone and ethyl trimethylsilylacetate in THF in the
presence of 10mol%
t
Bu-P4 base was carried out at
78
C, the condensation reaction
proceeded smoothly and the unsaturated ester was isolated in 94% yield (Table 5.7, run 1).
Other phophazene bases with weaker basicity, such as a
t
Bu-P2 base and BEMP, showed no
effect on the condensation under the same reaction conditions (runs 2, 3). DBU also showed
no catalytic effect on the condensation (run 4). When TBAF was used for the reaction, the
1,2-adduct was isolated in 38% yield, but no formation of alkene was observed [58] (run 5).
It was found that
t
Bu-P4 base is an excellent catalyst for the condensation, and the further
scope and limitations were investigated (Table 5.8). As another trimethylsilylalkyl sub-
strate, N,N-diethyltrimethylsilylacetamide was reacted with benzophenone to give the
unsaturated amide in 87% yield (run 1) and the reaction of trimethylsilylacetonitrile with
benzophenone was also successful, giving the arylacryronitorile in 78% yield (run 2).
Benzaldehyde was then used as a carbonyl compound and ethyl cinnamate was obtained in
89% yield using ethyl trimehylsilylacetate (run 3). Condensation of other arylaldehydes
with ethyl trimethylsilylacetate proceeded smoothly and the corresponding arylacrylates
O
O
1)
t
Bu-P4 base (10 mol%)
Ph-CHO, THF, rt, 24 h
NEt
2
O
2) AcOH-toluene, 100
o
C
TMS
Ph
76%
Scheme 5.37
Synthesis of phthalide
