Chemistry Reference
In-Depth Information
[101]. Degradation of polymers is an effective method to estimate the enantiometric
purity of optically active polymers. Thus, silicon-containing dialdehyde (
58
) and silicon-
containing bis(allylsilane) (
59
) were prepared and polymerized under the optimal
conditions. After polymerization, Si-C bonds were cleaved by treatment with tetrabu-
tylammonium fl uoride (TBAF) to give the corresponding homoallylic alcohol (
60
).
Thus, the enantiometric purity of the polymer was determined to be 57-72% by analyz-
ing
60
using chiral HPLC [105,106].
O
OH
OHC
CHO
i
-Pr
O
O
O
SiMe
3
O
O
R
O
B
Me
3
Si
O
2
C(CH
2
)
4
CO
2
R =
O
i
-Pr
Ar
54
55
Ar = 3,5-(CF
3
)
2
C
6
H
3
56
OH
OH
∗
O
O
∗
( )
4
O
O
n
57
OHC
CHO
OH
Me
3
Si
SiMe
3
S
Me
2
S
Me
2
59
60
58
OH
OHC
SiMe
3
SiMe
3
S
Me
2
S
Me
2
OHC
n
61
62
63
Chiral Lewis acid - catalyzed, one - component self - polyaddition of compounds (
61
,
62
)
possessing both a formyl group and an allylsilane moiety also affords optically active
polymers [107,108]. Chiral (acyloxy)borane (
56
) is highly effective for enantioselective
polymerization of
62
to give the optically active polymers (
63
), whose optical purity was
determined to be 78%, based on the degradation method [108].
13.2.1.5.3. Aldol Polymerization
Repetitive asymmetric Mukaiyama aldol reactions of
dialdehydes and bisenolates afford optically active poly(
- hydroxyester)s [98,109,110] .
For instance, the reaction of dialdehydes (
64
,
65
) and bis(triethylsilyl enol ether)s (
66
,
67
) in the presence of chiral Lewis acid (
68
) gave optically active polymers (
69
) with
high molecular weight [111]. The level of chiral induction in
69
was determined to be
66-76% ee by
1
H NMR analysis of the degradation products derived from
69
via Si - C
bond cleavages [111,112]. These results indicated that the high optical purity was
obtained by the asymmetric aldol polymerizations.
β
