Joon Seok Oh, Jongho Jeon, Do Yeon Park and Young Gyu Kim*
School of Chemical Engineering, Seoul National University, Seoul,
151-744, Republic of Korea. E-mail: ygkim@snu.ac.kr
Notes and references
1 S. C. Bergmeier, Tetrahedron, 2000, 56, 2561; D. J. Ager, I. Prakash and
D. R. Schaad, Chem. Rev., 1996, 96, 835.
2 Review: J. K. Cha and N.-S. Kim, Chem. Rev., 1995, 95, 1761.
3 Review for stereoselective dihydroxylation of allylic alcohols: J. K. Cha,
W. J. Christ and Y. Kishi, Tetrahedron, 1984, 40, 2247.
Fig. 1 Probable transition state models (PN 5 aryl ketimine).
4 A. N. Hulme and C. H. Montgomery, Tetrahedron Lett., 2003, 44, 7649.
5 R. E. Dolle, T. F. Herpin and Y. C. Shimshock, Tetrahedron Lett.,
2001, 42, 1855; M. F. Dee and R. L. Rosati, Bioorg. Med. Chem. Lett.,
1995, 5, 949.
6 Cyclic allylic amino derivatives: J. S. Oh, Y. S. Hong and Y. G. Kim,
J. Ind. Eng. Chem. (Seoul), 1997, 3, 326, Chem. Abs., 1998, 129,
202696z; K. Blades, T. J. Donohoe, J. J. G. Winter and G. Stemp,
Tetrahedron Lett., 2000, 41, 4701 and references therein.
Table 2 Dihydroxylation reactions of the derivatives of (Z)-c-amino-
a,b-unsaturated methyl ester (Scheme 1)
N-Boc derivative
Benzophenone ketimine
R
Ratioa (anti : syn) Yield (%) Ratioc (anti : syn) Yield (%)
Me
Bn
i-Bu
i-Pr
a
1 : 1.6
1 : 1.5
1 : 1
58 (24)b
82
1 : 5.4
1 : 15
1 : .50
1 : .100
90
71
80
66
´
7 J. C. Thoen, A. I. Morales-Ramos and M. A. Lipton, Org. Lett., 2002,
4, 4455.
65 (13)b
1 : 1.5
72 (25)b
8 Y. Huang, D. R. Dalton and P. J. Carroll, J. Org. Chem., 1997, 62, 372;
S. D. Broady, J. E. Rexhausen and E. J. Thomas, J. Chem. Soc., Perkin
Trans. 1, 1999, 1083.
9 J. Bra˚nalt, I. Kvarnstro¨m, B. Classon, B. Samuelsson, U. Nillroth,
U. H. Danielson, A. Karle´n and A. Hallberg, Tetrahedron Lett., 1997,
38, 3483.
10 J. S. Oh, D. Y. Park, B. S. Song, J. G. Bae, S. W. Yoon and Y. G. Kim,
Tetrahedron Lett., 2002, 43, 7209.
11 M. Iwashima, T. Kinsho and A. B. Smith, III, Tetrahedron Lett., 1995,
36, 2199.
Determined by 1H NMR.
Determined by G/C.
Recovered starting material.
b
c
constants and the NOE enhancement data, after conversion of
each amino diol product into the corresponding lactam.17 The
consistent high syn selectivity shown in the present study would be
useful in the synthesis of the related compounds since mixed results
were reported for a few (Z)-esters in the literature.8,18
12 D. J. Krysan, T. W. Rockway and A. R. Haight, Tetrahedron:
Asymmetry, 1994, 5, 625.
The selectivities observed in this study could be explained with
the Houk transition state models shown in Fig. 1.19 In the absence
of severe A1,3 allylic strain, the aryl ketimine group that is a
deactivating substituent would take preferentially an ‘N-inside’
conformation of the (E)-conjugated esters.20 Preferential osmy-
lation from the less hindered top side would give the anti diols. For
the (Z)-conjugated esters, severe allylic steric hindrance from the
methoxy carbonyl group would exist and the aryl ketimine group
is directed toward the outside to minimize the A1,3 interaction,
favouring an ‘N-outside’ conformation. Addition of OsO4 from
the bottom side of the ‘N-outside’ conformer would result in the
syn diol isomers as a major product. However, the Kishi empirical
models can be advanced to rationalize our results, too.2,21
In summary, a systematic study on the dihydroxylation
reactions of both (E)- and (Z)-c-amino-a,b-unsaturated esters
was performed and introduction of the aryl ketimine group into
allylic amine resulted in much improved stereoselectivity for their
osmium-catalysed dihydroxylation reactions. With the (E)-esters,
anti selectivity from 6.7 : 1 to 19 : 1 is obtained and the opposite
syn selectivity is observed with the (Z)-esters (5.4 : 1 to .100 : 1)
even without using expensive chiral auxiliaries. The stereoselective
results with the aryl ketimine derivatives are quite high compared
to those of the N-Boc derivatives. They are also complementary to
those of the N,N-dibenzyl derivatives for the (E)-esters. The
consistent syn selectivity with the (Z)-esters would be useful in
predicting the stereochemical outcome of dihydroxylation pro-
ducts. The potential of the present method is an efficient and
highly selective synthesis of natural or unnatural c-amino-
a,b-dihydroxy carboxylic acids and their derivatives. Application
of this strategy for the synthesis of two of the target compounds,
AGDHE and dihydroxyglutamic acid, is currently underway in
our laboratory.
13 A. R. Kumar and B. V. Rao, Tetrahedron Lett., 2003, 44, 5645.
14 M. Oba, S. Koguchi and K. Nishiyama, Tetrahedron, 2002, 58, 9359;
P. Dauban, C. Saint-Fuscien, F. Acher, L. Prezeau, I. Brabet, J. Pin and
R. H. Dodd, Bioorg. Med. Chem. Lett., 2000, 10, 129; P. Dauban,
C. Saint-Fuscien and R. H. Dodd, Tetrahedron, 1999, 55, 7589.
15 J. Jurczak and A. Golebiowski, Chem. Rev., 1989, 89, 149; M. T. Reetz,
Angew. Chem., Int. Ed. Engl., 1991, 30, 1531.
16 M. T. Reetz, T. J. Strack, F. Mutulis and R. Goddard, Tetrahedron
Lett., 1996, 37, 9293.
17 Both trans and cis lactams were prepared as follows from the N-Boc
amino diol derivatives that were separable by column chromatography.
Each N-Boc amino diol derivative was transformed into the N-Cbz
derivative that was treated with Pd/C and ammonium formate under
reflux to give the lactam diol. The following acetylation gave the
corresponding lactam diacetates shown below. The coupling constant of
3.7–4.0 Hz between H-4 and H-5 was assigned to the cis lactam and that
of 0 Hz to the trans lactam.8 Then, a mixture of ketimine diols was
independently transformed into the same lactams by following a similar
procedure described for the N-Cbz derivative above. The major lactam
derived from a mixture of ketimine diols matched the cis lactam
obtained from the N-Boc amino diol. The minor lactam was not seen
on the 1H NMR spectrum except when R is Me. The assignment of
relative configuration was confirmed by observation of the larger NOE
enhancement for the cis bicyclic lactam as shown below (cis lactam:
7.4% between H-4 and H-5; trans lactam: 2.8% between H-4 and H-5).
.
18 A. M. P. Koskinen and J. Chen, Tetrahedron Lett., 1991, 32, 6977.
19 K. N. Houk, H. Y. Duh, Y. D. Wu and S. R. Moses, J. Am. Chem.
Soc., 1986, 108, 2754.
20 F. Johnson, Chem. Rev., 1968, 68, 375; R. W. Hoffmann, Chem. Rev.,
1989, 89, 1841.
21 J. K. Cha, W. J. Christ and Y. Kishi, Tetrahedron Lett., 1983, 24, 3943;
J. K. Cha, W. J. Christ and Y. Kishi, Tetrahedron Lett., 1983, 24, 3947.
We thank the BK 21 Project for financial support.
This journal is ß The Royal Society of Chemistry 2005
Chem. Commun., 2005, 770–771 | 771