Chemistry Reference
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by CPL have been correlated to an organic compound with very high enantioenrich-
ments by asymmetric autocatalysis.
Further investigation is the direct correlation between CPL and enantioenriched
organic compound (Scheme 12.38). Thus, we performed the irradiation of CPL to the
asymmetric autocatalyst. (
R
) - and (
S
) - pyrimidyl alkanols
33
exhibit positive and negative
Cotton effects in circular dichroism (CD) spectra at 313 nm, respectively [105]. We
thought that the direct irradiation of racemic alkanol
33
by left - handed (
l
) CPL would
induce the asymmetric photodegradation of (
R
) - pyrimidyl alkanol
33
and leave the
slightly enantioenriched (
S
) -
33
. Even when the enantioenrichment of the remaining (
S
) -
pyrimidyl alkanol
33
is extremely low, as described in the preceding section, the com-
pound serves as an asymmetric autocatalyst in the subsequent asymmetric autocatalysis
with amplifi cation of chirality to produce itself with high enantioenrichment. Indeed,
direct irradiation of racemic
33
by left-handed CPL and the subsequent asymmetric
autocatalysis produces highly enantioenriched (
S
) - alkanol
33
with
99.5% ee (Scheme
12.38). On the other hand, irradiation with right-handed (
r
) CPL, instead of
l
- CPL,
formed (
R
) -
33
with
>
99.5% ee. The process provides direct correlation of the handedness
of CPL with that of the organic compound with high enantiomeric excess [105].
>
N
t
-Bu
N
OH
Rac
emate
33
r
-CPL
l
-CPL
Asymmetric photodegradation
N
N
t
-Bu
t
-Bu
N
OH
N
OH
Cryptochiral (
R
)-
33
Cryptochiral (
S
)-
33
N
t
-Bu
CHO
N
+
i
-Pr
2
Zn
32
Asymmetric autocatalysis
N
N
t
-Bu
t
-Bu
N
OH
N
OH
(
R
)-
33
>99.5% ee
(
S
)-
33
>99.5% ee
Scheme 12.38.
Short pathway to obtain a near enantiopure compound by CPL irradiation followed
by asymmetric autocatalysis.
