A HIGHLY STEREOCONTROLLED SYNTHESIS OF α-HYDROXYCYCLOPROPANES POSSESSING A TRIFLUOROMETHYL GROUP

Article abstract of DOI:10.1016/0957-4166(90)90031-5

The preparation of optically pure syn and anti-α-hydroxycyclopropanes possessing a trifluoromethyl group from stereoisomers of optically pure allylic alcohols by samarium-based carbenoids is described.

Full text of DOI:10.1016/0957-4166(90)90031-5

Tetrahedron:
Vol. 1.
Printed in Great Britain
A HIGHLY STEREOCONTROLLED SYNTHESIS OF
a-HYDROXYCYCLOPROPANES POSSESSING
A TRIFLUOROMETHYL GROUP
Takashi Yamazaki, Jenq Tain Lin, Mitsunori
and Tomoya Kitazume*
Department of Bioengineering, Tokyo Institute of Technology
Ookayama, Meguro-ku, Tokyo 152, Japan
(Received 20 April
The preparation of optically pure syn and
Abstract.
cyclopropanes possessing a trifluoromethyl group from stereoisomers
of optically pure allylic alcohols by samarium-based carbenoids
is described.
The stereoselective construction of organofluorine compounds is currently
of fundamental importance in such fields as the preparation of bioactive
materials and ferroelectric liquid
In particular, considerable attention
is being on the search for synthetic methods for the assembly of
contiguous stereocentres with high relative as well as absolute stereocontrol.
However, only a few methods are known for the control of stereochemistry of
fluorine containing molecules giving the diastereomeric and/or enantiomer
anti(erythro) or syn(threo)
We report herein the stereocontrolled synthesis of syn and/or anti
cyclopropyl carbinols possessing a trifluoromethyl group. We desired a
stereochemically controlled synthesis from starting materials of known absolute
configuration which would eliminate the need for diastereomeric separation.
Therefore, we chose to utilize the hydroxy-directed
of
or (S)-(E)- and/or or (S)-(Z)-allylic alcohols” possessing a trifluoromethyl
group. These substrates were found to have a dramatic effect on
diastereoselectivity of the cyclopropanation, giving only syn-isomer via the Houk
model shown in Figure I. In our case, we believe that samarium metal is more
tightly coordinated with the oxygen atom in the above Houk model, giving rise
to the higher diastereoselectivity.
351

et al.
No previous studies have examined the stereocontrolled synthesis of the
anti isomers (4). The syn isomers were oxidized with oxalyl chloride-dimethyl
sulphoxide, giving
the
(Scheme). To achieve the desired
we investigated the transformation of the
using a variety of reducing reagents.
stereocontrolled conversion to
optically pure cyclopropyl ketones
As the consequence, we found that L-selectride gave by far the highest
stereoselection. The desired stereocontrolled products were obtained in
moderate to good yields (Table).
OH
R’
R’
1
2
OH
0
C F
R ’
2
3
5
R
CF 3
R’
4
0°C
,
Sc h e m e

353
a-Hydroxycyclopropanes
Synthesis of cyclopropyl carbinols
Table
Yield
R
chemical shift
(J
Compd. R
No
Hz)
H
H
Ph
P h
87
60
(1.04) 0.82(d) 0.93-l
-46.4 (1.12)
Ph
H
H
86
87
1.08(d)
Ph
H
H
92
92
(1.13)
-16.7 (1.12)
83
89
(1.14)
-2.20 (1.16)
H
H
P h
P h
46
38
(1.03)
- 9 . 7 3
4
(S)
(R)
Ph
H
H
45
i-23.7 (0.92) 0.75(d) 0.94-l
=
3 4
37
(0.93)
0.72-l
H,
(1.15)
a) absolute configuration at C-l b)
ppm from ext.
in

T.
et al.
OH
OH
Anti
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