Chemistry Reference
In-Depth Information
O
1) catalyst I
C
2
H
4
, CH
2
Cl
2
2) catalyst II
C
2
H
4
, CH
2
Cl
2
O
Pd(OAc)
2
Bu
4
NOAc
PPh
3
, Na
2
CO
3
dioxane, 100 ºC
55%
O
127
24%
I
126
O
Me
3
Si
DDQ
LDA, SiMe
3
Cl
SiMe
3
THF,
−
40 ºC
CH
2
Cl
2
, 0 ºC
45%
70%
Me
3
Si
128
129
130
NaN(SiMe
3
)
2
O
2
, DMF,
O
−
40 ºC
26%
L
catalyst I: L = PCy
3
catalyst II: L =
O
Cl
Cl
Ru
NN
Mes
Mes
Ph
PCy
3
O
131
Scheme 42 Synthesis of chiral sumanene derivatives [
145
-
149
]
Pd-catalyzed
syn
-selective cyclotrimerization yielded
syn
-tris(norborneno)benzene
126 [
146
-
148
]. This newly developed protocol is more efficient than the conven-
tional method reported in Scheme
36
. Triketone 126 was converted to 127, which
was then subjected to ring-opening and ring-closing metathesis reactions by treat-
ment with catalysts I and II, respectively. The thus formed 128 underwent oxidative
aromatization at low temperature to give
sym
-trimethylsumanene (
C
)-129. The
bowl configuration of (
C
)-129 was confirmed by CD spectral measurements.
Treatment of (
C
)-129 with LDA and subsequently with chlorotrimethylsilane at
40
C yielded (
C
)-130, where all trimethylsilyl groups were
exo
-selectively
introduced. In contrast to (
C
)-129,(
C
)-130 has a high inversion barrier and was
not diastereomerized, even at room temperature. Chiral HPLC analysis of (
C
)-130
at room temperature enabled the determination of the enantiomeric excess (89%
ee). Additionally, chiral buckybowl 129 was able to undergo oxidation under mild
conditions (
40
C). Reaction of 129 with sodium hexamethyldisilazide under
oxygen atmosphere gave 131 in 26% yield [
149
].
The sumanene-type heterobuckybowls such as trithiasumanene 132 and
trisilasumanene 133 have also been prepared. The former was synthesized from a
regioisomeric mixture of tris(chloroethenyl)benzotrithiophenes under FVP conditions
at 1,000
C[
150
]. In contrast, trisilasumanene 133 was prepared by threefold sila-
Friedel-Crafts reactions [
151
]. The two heterobuckybowls provide a suitable model
for systematically studying the influences of the ring size on the structure (Table
7
).
