Chemistry Reference
In-Depth Information
O
∗
O
cat.
51
N
∗
+
48a
50b
∗
N
CH
2
O
∗
n
53
O
Scheme 13.10.
quantitative formation of optically active polymers (
53
), which showed a molar optical
rotation of [Φ ]
D
+243 ° (Scheme 13.10 ) [99] . α , β - Unsaturated esters (
49
) could also be
used as a bisdienophile monomer, which underwent polymerization with
50b
in the
presence of chiral oxazaborolidinone catalyst (
52
) to give polymers with [Φ ]
D
+42 ° , albeit
lower yield (66%) and molecular weight (2,700) [100].
O
O
N
R
N
R
O
O
48a
R =
50a
R =
CH
2
CH
2
CH
2
OCH
2
CH
2
OCH
2
CH
2
48b
R =
(CH
2
)
6
50b
R =
O
O
MeO
2
C
O
O
Al Cl
O
O
N
O
CO
2
Me
H
Ts
O
4
9
5
52
13.2.1.5.2. Allylation Polymerization
Lewis acid-catalyzed addition of allylsilanes to
aldehydes to give homoallylic alcohols, Sakurai-Hosomi reaction, is another powerful
tool for asymmetric condensation polymerization [98]. Repetitive allylation of dialde-
hydes and bis(allylsilane)s in the presence of chiral catalysts produced optically active
polymers having asymmetric carbons in the main chain [101,102]. Among the monomers
ever examined, dialdehyde (
54
) and bis(allylsilane) (
55
) showed excellent reactivity
toward asymmetric polymerization in the presence of chiral (acyloxy)borane (
56
)
[103,104] to give the polymer (
57
) with high molecular weight (14,000) and a high molar
optical rotation of [Φ ]
405
+1144° [101]. The optical purity of
57
was estimated to be
approximately 75% ee according to a model reaction between benzaldehyde and methal-
lyltrimethylsilane although the exact enantiometric purity of the polymer is still unknown
