- Email: [email protected]
Syntheses of highly constrained β-aryl isohexanoic acid derivatives via asymmetric Michael addition
Trtmhedron
Vol.
Lerrers,
31. No. 44, pp. 7917.7920.
Copyoght
0
1996 Elsevier
Printed in Great Britain.
PII: SOO40-4039(96)01795-9
All oghts reserved
0040.4039196
Syntheses of Highly Constrained P-Aryl Isohexanoic Derivatives Via Asymmetric Michael Addition
1996
Science Ltd
$15.00
+ 0.00
Acid
Subo Liao, Yinglin Han,’ Wei Qiu, Michael Bruck and Victor J. Hruby *
Department
Abstracts:
have been synthesized
crystal
structure
demonstrated restricted Copyright
The University
A series of enantiomerically
derivatives X-ray
of Chemistry,
of
with
0
1996
The stereoselective
p-isopropyl
Elsevier
pure highly
Tucson,
stetically
high diastereoselectivity
Arizona
hindered
85721
P-branched
via asymmetric
isohexanoic
Michael
acid
addition.
The
(4S,3’S)-3-[3’-(2,6-dimethylphenyl)isohexanyl]-4-phenyl-2-ox~olidinone
that the P+zonfiguration
by the bulky
of Arizona,
was induced
from
the Si-face,
group to the range expected
Science
from
and that the torsional molecular
angle x2 was
modeling.
Ltd
Michael addition of organometallic
reagents to a&unsaturated
acyl derivatives which
contain a chiral auxiliary is one of the most reliable methods to synthesize optically pure P-branched derivatives.lm4
Although various products
have been prepared with high diastereoselectivity
Michael additions to chiral oxazoline,’ ester,’ amide,4 or imide derivatives,’
carbonyl
via asymmetric
to our knowledge
there still have
not been any examples of the syntheses of highly sterically hindered P-branched carboxylic acids derivatives by this method.
As part of our efforts to design and synthesize
amino acids6
we have developed
enantiomerically
an efficient
various non-hindered
as an auxilliary.’ Using this methodology,
Grignard reagents in the presence of CuBrSMe,
be carried out with high stereoselectivity
address:
to prepare
these
constrained important
novel P-branched intermediates
(i.e.
pure P-methyl carboxylic acid derivatives) via asymmetric Michael addition by using optically
pure 4-phenyloxazolidinone
+ Permanent
procedure
conformationally
Nanjing
University
of Chemical
and in reasonable
Technology,
7917
Nanjing
the asymmetric Michael addition of
and the co-solvent dimethylsultide
yields.’
2looO9,
However,
P. R. China
could
in our initial attempts
to
7918
synthesize much more sterically-hindered magnesium
chloride
oxazolidinone,
to
the
p-isopropyl
Michael
aromatic amino acids, the Michael addition of isopropyl
acceptor,
(4R,2E)-3-[3’-(4-methoxyphenyl)propenoyl]-4-phenyl-2-
did not work well using the previously developed
chiral resolution
method to synthesize
Instead,
reaction conditions.
the desired optically pure intermediates
we applied a
of P-phenylisohexanoic
acid
derivatives.’ Recently, we have re-examined the asymmetric
syntheses
the asymmetric Michael reaction in order to develop a general approach for
of hindered
unusual p-isopropyl
aromatic amino acids.
acceptor, (4S,2E)-3-( 1-oxo-2-isohexenyl)-4-phenyl-2-oxazolidinone,
A new Michael reaction
was tested, and it was found that it could
react with a variety of aromatic Grignard reagents, including the highly sterically hindered 2’,6’-dimethylphenyl magnesium bromide under mild conditions. Ph
Ph
1.5 eq. RMgBr 0.15-l .O eq. CuBr.SMea
CH3 J-7
N
H3C
0
THF, -20 -
-5’ C
Y
+
0
0
Table 1. Diastereoselective R,
Syntheses of P-Aryl Isohexanoic Acid Derivatives R,
[a],""’
deb
Yield”
Au(Hz)*
Entry
R,
1
H
H
H
82%
>90%
+9.7”
57.2
OCH,
H
H
97%
>90%
+6.0”
56.8
CH,
H
94%
>90%
+7.3”
69.9
CH, CH,
CH, CH,
68%
>90%
+7.6”
98.9
86%
>90%
+6.6”
98.6
2 3 4
OCH, H
5
OCH,
a. The yield was calculated determined
from ‘H NMR
[c] = lmg/mL
in
CDCI,:.
from the weight of product of crude product,”
d.
AU is
the chemical
de>90%
after column
chromatography
means that no diasteroisomer
shift difference
purification;
b. The de was
was observed from
between the two methyl
groups
‘H NMR; c
of the P-isopropyl
group. As compared to the previously reported reaction conditions,’ we have found the reactions of the phenyl or substituted phenyl Grignard reagents only require catalytic amounts of CuBrSMe, co-solvent.
However, the para-methoxylated
secure the complete conjugation
and no dimethylsultide
phenyl Grignard reagents needed one equivalent of CuBrSMe,
addition reaction.
Otherwise,
1,2-addition
reactions could be observed,
even became the major reaction pathway.’ The reason why phenyl and para-methoxyphenyl require different investigation.
amounts
for 1,4-conjugation
addition
to and
Grignard reagents
is still not clear,
and is under
In any case, all products were obtained in good to excellent yields with high optical purity (Table
1). These P-branched p-isopropyl
of Cu(1) catalyst
as
isohexanoic
acid derivatives could be easily converted into their corresponding
aromatic amino acids using chemistry previously elaborated in our laboratory.’
unusual
7919
An X-ray crystal structure of the compound oxazolidinone asymmetric
4 has been determined
(4S,3’S)-3-[3’-(2,6-dimethylphenyl)isohexanyl]-4-phenyl-2-
and the results are shown in Figure 1. These results suggested
synthesis, the P-carbon configuration
that in the
was induced from the Si-face presumably because the Re-face
was shielded by the phenyl ring of the oxazolidinone
in the Michael reaction transition state,’ and the rotation of
aromatic ring is found to be &=+112.6” which is in the angle range expected from computer modeling.” chemical shift differences constraint in these @ryl of methyl substituents
(Au) of the two isopropyl isohexanoic
acid derivatives.
methyl groups could be used to assess
The
the degree of
As seen from the Table 1, Au increases with the number 1 and
on the aromatic ring. Compounds 4 and 5 have the largest Au values, compounds
2 the smallest Au value. The para-methoxy
substituent on the aromatic ring has no effects on Au values.
the presence of the 2’ and 6’-dimethyl groups and of the p-isopropyl reduce greatly the flexibility preparation of P-isopropyl
of p-aryl
isohexanoic
Thus,
group produce torsional constraints
acid derivatives,
which
are important
which
precursors
for
aromatic ammo acids.
Figure I. The Stereo view of the crystal structure of (4S, 3’S)-3-[3’-(2,6-dimethylphenyl)isohexanyl]-4-phenyl-2-oxazolidinone
Experimental 0.15 equivalents
Procedures:
except
To a mixture of RMgBr (1.7
for para-methoxyphenyl
magnesium
mmol,
bromide
4
1.5 equivalents)
and
CuBrSMe,
which needs 1 .O equivalent)
in
-20°C was added dropwise a solution of (4S,2E)-3-( I-oxo-2-isohexenyl)-4-phenyl-2-oxazohdinone I.0 equivalent)
in 3 mL of freshly
resulting mixture was kept stirring hour.
The reaction
distilled THF. at -15°C
was then quenched
with ether (3 x 20 mL). The combined dried
over anhydrous
purified
magnesium
with 20 mL of saturated ammonium organic extracts
sulfate.
After
during
the addition
to room
chloride,
temperature
of dried
organic
mmol,
process. during
The one
and the product was extracted
were washed with brine (2 x 20 mL),
evaporation
(1.16
water (20
phases, the crude
mL). and
product
was
by silica gel chromatography.
Acknowledgments: about this research, and Health
A yellow color was observed
for two hours, then slowly warmed
(36 mg,
5 mL THF at
Service
The authors wish to acknowledge the financial
DK 2 1085
support
of grants from
NIDA
Prof. R. S. Glass for very helpful discussions DA 06284
and DA 08657,
and US.
Public
7920
References and Notes a) Tomioka, K. and Koga, K. in “Asymmetric Synthesis”, Ed., Morrison, J.D. Academic Press, 1983, Vol. 2, 201-224. b) Barner, B.A. and Meyers, A.I. J. Am. Chem. Sot. 1984, 106, 18651866. C) Oppolzer, W.; Poli, G.; Kingma, A.J.; Starkemann, C. and Bemardinelli, G. Helv. Chim Acta. 1987, 70, 2201-2214. 2.
a) Meyers, A.I. and Whitten, C.E. .I. Am. Chem. Sot. 1975, Shipman, M. J. Org. Chem. 1991. 56, 7098-7102.
3.
a) Fang, C.; Ogawa, T.; Suemune, H. and Sakai, K. Tetrtlhedron: Asymmetry b) Kawana, M. and Emoto, S. Bull. Chem. Sot. Jpn. 1966,39, 910-916.
4.
a) Mukaiyama, T. and Iwasawa, N. Chem. Lett. 1981, Bown, E. Tetrahedron: Asymmetry 1992, 3, 587-590.
5.
a) Melnyk, 0.; Stephan, E.; Pourcelot, C. and Cresson, P. Tetrahedron 1992, Tomioka, K.; Suenaga, T. and Koga, K. Tetrahedron lett. 1986, 27, 369-372.
6.
1993, (a) Hruby, V. J. Biopolymers W. Biochem. J. 1990,268, 249-262.
7.
(a) Dharanipragada, R.; VanHulle, K.; Bannister, A.; Bear, S.; Kennedy, L. and Hruby, V. J. Tetrahedron 1992,48,4733-4748; (b) Nicolas, E.; Russell, K.C.; Hruby, V.J. J. Org. Chem. 1993, 58, 7766-7770; (c) Nicolas, E.; Russell, K.C.; Knollenberg, J. and Hruby, V.J. J. Org. Chem. 1993, 58,7565 -7571; (d) Jiao, D.; Russell, K.C. and Hruby, V.J. Tetrahedron 1993, 49, 351 l- 3520; (e) Li, G.; Patel, D.; and Hruby, V.J. J. Chem. Sot. Per!& Trans. I 1994, 3057-3059; (f) Qian, X.; Russell, K. C.; Boteju, L.W. and Hruby, V. J. Tetrahedron 1995,51, 1033-1054.
8.
Liao, S. and Hruby, V. J. Tetrahedron
9.
LOW, B-S.; Li, G.; Lung, F-D. and Hruby, V.J. J. Org. Chem. 1995, 60, 5509-5514.
10.
Shenderovich,
11.
‘HNMR: sppm 2. 7.20-6.74(m, 9H, aromatic protons), 5.31(dd, J=8.7, 4.Hz, lH, oxazolidinone, CHAr-), 4.58(t, J=8.7Hz, lH, oxazolidinone, -CH,-/proR), 4.08(dd, J=7.1, 4.8Hz, lH, oxazolidinone, -CH,-/pros), 3.80(s, 3H, -ArOCH,), 3.74(dd, J=15.5, 5.2Hz, lH, -C,H-/pros), 3.07(dd, J=15.5, 5.1Hz, lH, -C,H-/proR), 2.87(m, lH, -C,H-), 1.83[m, lH, -CH(CH,),], 0.95(d, J=6.7Hz, 3H, -CH,), 0.72(d, J=6.7Hz, 3H, -CH,); 3. 7.20-6.52(m, 8H, aromatic protons), 5,28(dd, J=8.7, 4.1Hz, lH, oxazolidinone, -CHAr-), 4.53(t, J=8.8Hz, lH, oxazolidinone, -CH,-/proR), 4.04(dd, J=8.7, 4. lHz, lH, oxazolidinone, -CH,/proS), 3.80(dd, J= 15.0, lO.OHz, lH, -C,H-/pros ), 3.79(s, 3H, -ArOCH,), 3.13(m, lH, -C,H-), 2.97(dd, J=15.0, 4.7Hz, lH, -C,H/proR), 2.07(s, 3H, -ArCH,), 1.81[m, lH, CH(CH,),], l.OO(d, J=6.6Hz, 3H, CH,), 0.72(d, J=6.7Hz, 3H, -CH,); 4. 7.25-6.83(m, 8H, aromatic protons), 5.31(dd, J=8.74, 4.OHz, lH, oxazohdinone -CHAr-), 4.60(t, J=8.7Hz, IH, oxazolidinone, CH,-/proR), 4.13(dd, J=8.7, 4.1Hz, lH, oxazolidinone, -CH,-/pros), 3.64-3.35(m, 3H, -C,H,C,H-), 2.45(s, 3H, -CH,), 2.25-2.18[m, lH, -CH(CH,),], 2.17(s, 3H, -CH,), l.O6(d, J=6.4Hz, 3H, -CH,), 0.66(d, J=6.7Hz, 3H, -CH,); 5. 7.26-6.39(m, 7H, aromatic protons), 5.31(dd, J=8.7, 4.OHz, lH, oxazolidinone, -CHAr-), 4.59(t, J=8.7Hz, IH, oxazolidinone, -CH,/proR), 4.13(dd, J=8.8, 4.OHz, H, oxazolidinone, -CH,-/pros), 3.74(s, 3H, -ArOCH,), 3.65(dd, J=15.0, 7.8Hz, lH, -C,H-/pros), 3.503.27(m, 2H, -C,H-/proR and -C,H-), 2.43(s, 3H, -ArCH,), 2.14[m, lH, -CH(CH,),], 2.13(s, 3H, ArCH3). l.O5(d, J=6.5Hz, 3H, CH,), 0.66(d, J=6.7Hz, 3H, -CH,).
1073-1082;
97, 6266-6267.
9 13-916.
b) Meyers, A.I. and 1991,
b) Touet, J.;
2, 389-398.
Baudouin,
S. and
48, 841-850.
b)
(b) Hruby, V. J.; Al-Obeidi, F. and Kazmierski,
Lett.. 1996, 37, 1563-1566.
M.; Liao, S. and Hruby, V.J. unpublished
results.
(Received in USA 9 July 1996; revised 3 September 1996; accepted 9 September 1996)
Vol.
Lerrers,
31. No. 44, pp. 7917.7920.
Copyoght
0
1996 Elsevier
Printed in Great Britain.
PII: SOO40-4039(96)01795-9
All oghts reserved
0040.4039196
Syntheses of Highly Constrained P-Aryl Isohexanoic Derivatives Via Asymmetric Michael Addition
1996
Science Ltd
$15.00
+ 0.00
Acid
Subo Liao, Yinglin Han,’ Wei Qiu, Michael Bruck and Victor J. Hruby *
Department
Abstracts:
have been synthesized
crystal
structure
demonstrated restricted Copyright
The University
A series of enantiomerically
derivatives X-ray
of Chemistry,
of
with
0
1996
The stereoselective
p-isopropyl
Elsevier
pure highly
Tucson,
stetically
high diastereoselectivity
Arizona
hindered
85721
P-branched
via asymmetric
isohexanoic
Michael
acid
addition.
The
(4S,3’S)-3-[3’-(2,6-dimethylphenyl)isohexanyl]-4-phenyl-2-ox~olidinone
that the P+zonfiguration
by the bulky
of Arizona,
was induced
from
the Si-face,
group to the range expected
Science
from
and that the torsional molecular
angle x2 was
modeling.
Ltd
Michael addition of organometallic
reagents to a&unsaturated
acyl derivatives which
contain a chiral auxiliary is one of the most reliable methods to synthesize optically pure P-branched derivatives.lm4
Although various products
have been prepared with high diastereoselectivity
Michael additions to chiral oxazoline,’ ester,’ amide,4 or imide derivatives,’
carbonyl
via asymmetric
to our knowledge
there still have
not been any examples of the syntheses of highly sterically hindered P-branched carboxylic acids derivatives by this method.
As part of our efforts to design and synthesize
amino acids6
we have developed
enantiomerically
an efficient
various non-hindered
as an auxilliary.’ Using this methodology,
Grignard reagents in the presence of CuBrSMe,
be carried out with high stereoselectivity
address:
to prepare
these
constrained important
novel P-branched intermediates
(i.e.
pure P-methyl carboxylic acid derivatives) via asymmetric Michael addition by using optically
pure 4-phenyloxazolidinone
+ Permanent
procedure
conformationally
Nanjing
University
of Chemical
and in reasonable
Technology,
7917
Nanjing
the asymmetric Michael addition of
and the co-solvent dimethylsultide
yields.’
2looO9,
However,
P. R. China
could
in our initial attempts
to
7918
synthesize much more sterically-hindered magnesium
chloride
oxazolidinone,
to
the
p-isopropyl
Michael
aromatic amino acids, the Michael addition of isopropyl
acceptor,
(4R,2E)-3-[3’-(4-methoxyphenyl)propenoyl]-4-phenyl-2-
did not work well using the previously developed
chiral resolution
method to synthesize
Instead,
reaction conditions.
the desired optically pure intermediates
we applied a
of P-phenylisohexanoic
acid
derivatives.’ Recently, we have re-examined the asymmetric
syntheses
the asymmetric Michael reaction in order to develop a general approach for
of hindered
unusual p-isopropyl
aromatic amino acids.
acceptor, (4S,2E)-3-( 1-oxo-2-isohexenyl)-4-phenyl-2-oxazolidinone,
A new Michael reaction
was tested, and it was found that it could
react with a variety of aromatic Grignard reagents, including the highly sterically hindered 2’,6’-dimethylphenyl magnesium bromide under mild conditions. Ph
Ph
1.5 eq. RMgBr 0.15-l .O eq. CuBr.SMea
CH3 J-7
N
H3C
0
THF, -20 -
-5’ C
Y
+
0
0
Table 1. Diastereoselective R,
Syntheses of P-Aryl Isohexanoic Acid Derivatives R,
[a],""’
deb
Yield”
Au(Hz)*
Entry
R,
1
H
H
H
82%
>90%
+9.7”
57.2
OCH,
H
H
97%
>90%
+6.0”
56.8
CH,
H
94%
>90%
+7.3”
69.9
CH, CH,
CH, CH,
68%
>90%
+7.6”
98.9
86%
>90%
+6.6”
98.6
2 3 4
OCH, H
5
OCH,
a. The yield was calculated determined
from ‘H NMR
[c] = lmg/mL
in
CDCI,:.
from the weight of product of crude product,”
d.
AU is
the chemical
de>90%
after column
chromatography
means that no diasteroisomer
shift difference
purification;
b. The de was
was observed from
between the two methyl
groups
‘H NMR; c
of the P-isopropyl
group. As compared to the previously reported reaction conditions,’ we have found the reactions of the phenyl or substituted phenyl Grignard reagents only require catalytic amounts of CuBrSMe, co-solvent.
However, the para-methoxylated
secure the complete conjugation
and no dimethylsultide
phenyl Grignard reagents needed one equivalent of CuBrSMe,
addition reaction.
Otherwise,
1,2-addition
reactions could be observed,
even became the major reaction pathway.’ The reason why phenyl and para-methoxyphenyl require different investigation.
amounts
for 1,4-conjugation
addition
to and
Grignard reagents
is still not clear,
and is under
In any case, all products were obtained in good to excellent yields with high optical purity (Table
1). These P-branched p-isopropyl
of Cu(1) catalyst
as
isohexanoic
acid derivatives could be easily converted into their corresponding
aromatic amino acids using chemistry previously elaborated in our laboratory.’
unusual
7919
An X-ray crystal structure of the compound oxazolidinone asymmetric
4 has been determined
(4S,3’S)-3-[3’-(2,6-dimethylphenyl)isohexanyl]-4-phenyl-2-
and the results are shown in Figure 1. These results suggested
synthesis, the P-carbon configuration
that in the
was induced from the Si-face presumably because the Re-face
was shielded by the phenyl ring of the oxazolidinone
in the Michael reaction transition state,’ and the rotation of
aromatic ring is found to be &=+112.6” which is in the angle range expected from computer modeling.” chemical shift differences constraint in these @ryl of methyl substituents
(Au) of the two isopropyl isohexanoic
acid derivatives.
methyl groups could be used to assess
The
the degree of
As seen from the Table 1, Au increases with the number 1 and
on the aromatic ring. Compounds 4 and 5 have the largest Au values, compounds
2 the smallest Au value. The para-methoxy
substituent on the aromatic ring has no effects on Au values.
the presence of the 2’ and 6’-dimethyl groups and of the p-isopropyl reduce greatly the flexibility preparation of P-isopropyl
of p-aryl
isohexanoic
Thus,
group produce torsional constraints
acid derivatives,
which
are important
which
precursors
for
aromatic ammo acids.
Figure I. The Stereo view of the crystal structure of (4S, 3’S)-3-[3’-(2,6-dimethylphenyl)isohexanyl]-4-phenyl-2-oxazolidinone
Experimental 0.15 equivalents
Procedures:
except
To a mixture of RMgBr (1.7
for para-methoxyphenyl
magnesium
mmol,
bromide
4
1.5 equivalents)
and
CuBrSMe,
which needs 1 .O equivalent)
in
-20°C was added dropwise a solution of (4S,2E)-3-( I-oxo-2-isohexenyl)-4-phenyl-2-oxazohdinone I.0 equivalent)
in 3 mL of freshly
resulting mixture was kept stirring hour.
The reaction
distilled THF. at -15°C
was then quenched
with ether (3 x 20 mL). The combined dried
over anhydrous
purified
magnesium
with 20 mL of saturated ammonium organic extracts
sulfate.
After
during
the addition
to room
chloride,
temperature
of dried
organic
mmol,
process. during
The one
and the product was extracted
were washed with brine (2 x 20 mL),
evaporation
(1.16
water (20
phases, the crude
mL). and
product
was
by silica gel chromatography.
Acknowledgments: about this research, and Health
A yellow color was observed
for two hours, then slowly warmed
(36 mg,
5 mL THF at
Service
The authors wish to acknowledge the financial
DK 2 1085
support
of grants from
NIDA
Prof. R. S. Glass for very helpful discussions DA 06284
and DA 08657,
and US.
Public
7920
References and Notes a) Tomioka, K. and Koga, K. in “Asymmetric Synthesis”, Ed., Morrison, J.D. Academic Press, 1983, Vol. 2, 201-224. b) Barner, B.A. and Meyers, A.I. J. Am. Chem. Sot. 1984, 106, 18651866. C) Oppolzer, W.; Poli, G.; Kingma, A.J.; Starkemann, C. and Bemardinelli, G. Helv. Chim Acta. 1987, 70, 2201-2214. 2.
a) Meyers, A.I. and Whitten, C.E. .I. Am. Chem. Sot. 1975, Shipman, M. J. Org. Chem. 1991. 56, 7098-7102.
3.
a) Fang, C.; Ogawa, T.; Suemune, H. and Sakai, K. Tetrtlhedron: Asymmetry b) Kawana, M. and Emoto, S. Bull. Chem. Sot. Jpn. 1966,39, 910-916.
4.
a) Mukaiyama, T. and Iwasawa, N. Chem. Lett. 1981, Bown, E. Tetrahedron: Asymmetry 1992, 3, 587-590.
5.
a) Melnyk, 0.; Stephan, E.; Pourcelot, C. and Cresson, P. Tetrahedron 1992, Tomioka, K.; Suenaga, T. and Koga, K. Tetrahedron lett. 1986, 27, 369-372.
6.
1993, (a) Hruby, V. J. Biopolymers W. Biochem. J. 1990,268, 249-262.
7.
(a) Dharanipragada, R.; VanHulle, K.; Bannister, A.; Bear, S.; Kennedy, L. and Hruby, V. J. Tetrahedron 1992,48,4733-4748; (b) Nicolas, E.; Russell, K.C.; Hruby, V.J. J. Org. Chem. 1993, 58, 7766-7770; (c) Nicolas, E.; Russell, K.C.; Knollenberg, J. and Hruby, V.J. J. Org. Chem. 1993, 58,7565 -7571; (d) Jiao, D.; Russell, K.C. and Hruby, V.J. Tetrahedron 1993, 49, 351 l- 3520; (e) Li, G.; Patel, D.; and Hruby, V.J. J. Chem. Sot. Per!& Trans. I 1994, 3057-3059; (f) Qian, X.; Russell, K. C.; Boteju, L.W. and Hruby, V. J. Tetrahedron 1995,51, 1033-1054.
8.
Liao, S. and Hruby, V. J. Tetrahedron
9.
LOW, B-S.; Li, G.; Lung, F-D. and Hruby, V.J. J. Org. Chem. 1995, 60, 5509-5514.
10.
Shenderovich,
11.
‘HNMR: sppm 2. 7.20-6.74(m, 9H, aromatic protons), 5.31(dd, J=8.7, 4.Hz, lH, oxazolidinone, CHAr-), 4.58(t, J=8.7Hz, lH, oxazolidinone, -CH,-/proR), 4.08(dd, J=7.1, 4.8Hz, lH, oxazolidinone, -CH,-/pros), 3.80(s, 3H, -ArOCH,), 3.74(dd, J=15.5, 5.2Hz, lH, -C,H-/pros), 3.07(dd, J=15.5, 5.1Hz, lH, -C,H-/proR), 2.87(m, lH, -C,H-), 1.83[m, lH, -CH(CH,),], 0.95(d, J=6.7Hz, 3H, -CH,), 0.72(d, J=6.7Hz, 3H, -CH,); 3. 7.20-6.52(m, 8H, aromatic protons), 5,28(dd, J=8.7, 4.1Hz, lH, oxazolidinone, -CHAr-), 4.53(t, J=8.8Hz, lH, oxazolidinone, -CH,-/proR), 4.04(dd, J=8.7, 4. lHz, lH, oxazolidinone, -CH,/proS), 3.80(dd, J= 15.0, lO.OHz, lH, -C,H-/pros ), 3.79(s, 3H, -ArOCH,), 3.13(m, lH, -C,H-), 2.97(dd, J=15.0, 4.7Hz, lH, -C,H/proR), 2.07(s, 3H, -ArCH,), 1.81[m, lH, CH(CH,),], l.OO(d, J=6.6Hz, 3H, CH,), 0.72(d, J=6.7Hz, 3H, -CH,); 4. 7.25-6.83(m, 8H, aromatic protons), 5.31(dd, J=8.74, 4.OHz, lH, oxazohdinone -CHAr-), 4.60(t, J=8.7Hz, IH, oxazolidinone, CH,-/proR), 4.13(dd, J=8.7, 4.1Hz, lH, oxazolidinone, -CH,-/pros), 3.64-3.35(m, 3H, -C,H,C,H-), 2.45(s, 3H, -CH,), 2.25-2.18[m, lH, -CH(CH,),], 2.17(s, 3H, -CH,), l.O6(d, J=6.4Hz, 3H, -CH,), 0.66(d, J=6.7Hz, 3H, -CH,); 5. 7.26-6.39(m, 7H, aromatic protons), 5.31(dd, J=8.7, 4.OHz, lH, oxazolidinone, -CHAr-), 4.59(t, J=8.7Hz, IH, oxazolidinone, -CH,/proR), 4.13(dd, J=8.8, 4.OHz, H, oxazolidinone, -CH,-/pros), 3.74(s, 3H, -ArOCH,), 3.65(dd, J=15.0, 7.8Hz, lH, -C,H-/pros), 3.503.27(m, 2H, -C,H-/proR and -C,H-), 2.43(s, 3H, -ArCH,), 2.14[m, lH, -CH(CH,),], 2.13(s, 3H, ArCH3). l.O5(d, J=6.5Hz, 3H, CH,), 0.66(d, J=6.7Hz, 3H, -CH,).
1073-1082;
97, 6266-6267.
9 13-916.
b) Meyers, A.I. and 1991,
b) Touet, J.;
2, 389-398.
Baudouin,
S. and
48, 841-850.
b)
(b) Hruby, V. J.; Al-Obeidi, F. and Kazmierski,
Lett.. 1996, 37, 1563-1566.
M.; Liao, S. and Hruby, V.J. unpublished
results.
(Received in USA 9 July 1996; revised 3 September 1996; accepted 9 September 1996)