Chiral vanadium-based catalysts for asymmetric epoxidation of allylic alcohols

Full text of DOI:10.1021/jo9821933

3
38
J . Org. Chem. 1999, 64, 338-339
Sch em e 1a
Ch ir a l Va n a d iu m -Ba sed Ca ta lysts for
Asym m etr ic Ep oxid a tion of Allylic Alcoh ols
Noriaki Murase, Yujiro Hoshino, Masataka Oishi, and
Hisashi Yamamoto*
Graduate School of Engineering, Nagoya University, CREST,
J apan Science and Technology Corporation (J ST),
Chikusa, Nagoya, 464-8603, J apan
Received November 3, 1998
The asymmetric oxidation of unfunctionalized as well as
functionalized olefins is a subject of current interest and
intensive research in organic synthesis.1 The sharpless
asymmetric epoxidation protocol of allylic alcohols has
proven to be an extremely useful means of synthesizing
a
Key: (a) (COCl) , cat.DMF, CH Cl ; (b) 3, NEt , CH Cl ; (c) t-BuLi,
2
2
2
3
2
2
THF, -78 to 0 °C.
2
enantiomerically enriched compounds. In comparison with
Ta ble 1. Ca ta lytic En a n tioselective Ep oxid a tion of
the titanium catalysts, only a few examples of chiral
vanadium catalysts for the epoxidation have been reported
so far,3 although VO(acac)2 is the catalyst of choice for
tr a n s-2,3-Dip h en yl-2-p r op en ola
4
stereoselective epoxidation of allylic alcohols. Since during
the course of oxidation both vanadium(IV) and -(V) are
5
thought to exist as an oxovanadium(V) complex that has
three alkoxy groups for substrates, hydroperoxides, and
ligands, ligand design of chiral vanadium catalysts has never
been successfully established to control such a complexation
c
entry
catalyst
ROOHb
conditions (°C, h)
ee (%)
6
mode as proposed by Sharpless (vide infra). We report here
1
2
3
VO(acac)2/1a
CHP
CHP
CHP
0, 6 days
0, 8 days
0, 19
25
54
65
new chiral hydroxamic acids derived from 2,2′-binaphthol
that serve as monovalent ligands with a vanadium complex
for the catalytic asymmetric epoxidation of allylic alcohols.
1b
1c
i
4
5
6
7
8
VO(OPr )3/1c
CHP
0, 3
68
40
86
83
73
TBHP
TrOOH
TrOOH
TrOOH
-40, 10
-20, 68
-20, 24
-20, 24
d
e
a
Unless otherwise noted, the reaction was carried out in toluene
in the presence of vanadium complex (5 mol %) and 1 (15 mol %).
b
The isolated yield in each entry was around 80%. CHP )
cumenehydroperoxide, TBHP ) tert-butyl hydroperoxide, TrOOH
)
triphenylmethyl hydroperoxide. c The absolute configuration of
Our first attempt to modify optically active known 2
derived from binaphthol in several steps involved conversion
of the carboxylic acid into a hydroxamic acid group that has
the major enantiomer in each run was 2S,3S, and the ee values
d
were determined by chiral HPLC (column, OD-H) analysis. 7.5
mol % of 1c. e 6.0 mol % of 1c.
high affinity to vanadium complexes as outlined in Scheme
7
1
. Transformation of 2 to 1 was carried out in the usual
manner via reaction of the corresponding acid chloride with
several hydroxylamines 3 in the presence of NEt3 to furnish
hydroxamic acid 1. Coupling reaction of the acid chloride
with 3c gave 1c together with a significant amount of the
undesired O-acylated byproduct 1c′, which underwent smooth
isomerization to 1c by treatment with t-BuLi under the mild
conditions.
(1) (a) Sharpless, K. B.; Finn, M. G. In Asymmetric Synthesis; Morrison,
J . D., Ed.; Academic Press: London, 1985; Vol. 5, pp 247-308. (b) H o¨ ft, E.
Top. Curr. Chem. 1993, 164, 63. (c) Pedragosa-Moreau, S.; Archelas, A.;
Furstoss, R. Bull. Soc. Chim. Fr. 1995, 132, 769.
(
2) (a) Katsuki, T.; Sharpless, K. B. J . Am. Chem. Soc. 1980, 102, 5974.
(
b) Rossiter, B. E. In Asymmetric Synthesis; Morrison, J . D., Ed.; Academic
Press: London, 1985; Vol. 5, pp 193-246. (c) Gao, Y.; Hanson, R. M.;
Klunder, J . M.; Ko, S. Y.; Masamune, H.; Sharpless, K. B. J . Am. Chem.
Soc. 1987, 109, 5765. (d) Finn, M. G.; Sharpless, K. B. J . Am. Chem. Soc.
Then, we set out to test epoxidation of trans-2,3-diphenyl-
2
%
-propenol in the presence of a vanadium catalyst (5 mol
) and a small excess of 1 under various reaction conditions
1
991, 113, 113
3) For chiral molybdenum and vanadium catalysts for asymmetric
(
epoxidation of allylic alcohols: (a) Yamada, S.; Mashiko, T.; Terashima, S.
J . Am. Chem. Soc. 1977, 99, 1988. (b) Michaelson, R. C.; Palermo, R. E.;
Sharpless, K. B. J . Am. Chem. Soc. 1977, 99, 1990. (c) Sharpless, K. B.;
Verhoeven, T. R. Aldrichim. Acta 1979, 12, 63 and a reference therein. (d)
Bolm, C.; Luong, T. K. K.; Harms, K. Chem. Ber./ Recueil 1997, 130, 887.
(Table 1). The epoxidation rate is highly dependent on the
structure of the hydroxylamine moiety and the oxidation
state of starting vanadium complexes. Sterical hindrance
and/or π-electronic properties of both the N-alkyl group of 1
and the alkyl group of peroxides led to a dramatic increase
in enantioselectivity (entries 1 and 6). The higher oxidation
state (V) might facilitate clean generation of the chiral active
species (entries 3 and 4). In place of toluene, CH2Cl2 can
also be used as solvent, but the enantioselectivity falls
significantly (from 86 to 62%). It should be noted that the
ee value of 73% was observed even when 1.2 equiv of 1c
based on vanadium were employed. These results support
our hypothesis that a 1:1 complex between vanadium(V) and
(4) For achiral metal-catalyzed regio- and stereoselective epoxidation of
allylic alcohols, see: (a) Sharpless, K. B.; Michaelson,, R. C. J . Am. Chem.
Soc. 1973, 95, 6136. (b) Tanaka, S.; Yamamoto, H.; Nozaki, H.; Sharpless,
K. B.; Michaelson, R. C.; Cutting, J . D. J . Am. Chem. Soc. 1974, 96, 5254.
(
5) (a) Gould, E. S.; Hiatt, R. R.; Irwin, K. C. J . Am. Chem. Soc. 1968,
0, 4573. (b) Cenci, S.; Furia, F. D.; Modena, G.; Curci, R.; Edwards, J . O.
J . Chem. Soc., Chem. Commun. 1978, 979.
6) Berrisford, D. J .; Bolm, C.; Sharpless, K. B. Angew. Chem., Int. Ed.
Engl. 1995, 34, 1059.
7) (a) Miyano, S.; Okada, S.; Suzuki, T.; Handa, S.; Hashimoto, H Bull.
9
(
(
Chem. Soc. J pn. 1986, 59, 2044. (b) Miyano, S.; Hotta, H.; Takeda, M.;
Kabuto, C.; Hashimoto, H. Bull. Chem. Soc. J pn. 1989, 52, 1528.
1
0.1021/jo9821933 CCC: $18.00 © 1999 American Chemical Society
Published on Web 01/05/1999

Communications
J . Org. Chem., Vol. 64, No. 2, 1999 339
Ta ble 2. Ca ta lytic Ep oxid a tion of Va r iou s Su bstitu ted
To explore further the potential of these new catalysts,
we examined epoxidation of various substituted allyl alcohols
under the optimized conditions in Table 1, and these results
are summarized in Table 2. Epoxidation of 3,3-disubstituted
i
a
Allyl Alcoh ols in th e P r esen ce of VO(OP r )3/1c
i
allyl alcohols using catalytic VO(OPr )3 with 1c proceeded
smoothly to yield the corresponding epoxides in moderate
to good yields with mediocre selectivities (entries 1-3). On
the other hand, in the case of 2,3-disubstituted allyl alcohols,
irrespective of bearing aromatic groups, a uniformly high
degree of enantioselectivities around 90% was obtained
(
1
entries 4-6). Notably, the productivity of our catalyst for
-cyclopentenylmethanol is superior to the stoichiometric
9
epoxidation with the titanium tartrate (entry 6). Monosub-
stituted allyl alcohols gave unsatisfactory results. A typical
procedure is as follows (entry 4 in Table 2): To a solution of
the chiral vanadium catalyst (9.8 mM, 12.7 µmol) readily
i
prepared from 1c and VO(OPr )3 in dry toluene (25 °C, 1 h)
were added trans-2-methylcinnamyl alcohol (0.254 mmol)
and trityl hydroperoxide (0.381 mmol) at -20 °C under argon
atmosphere. After the solution was stirred for 48 h at this
temperature, the reaction was quenched by addition of
saturated Na2SO3 (aq) (2 mL). Extraction of the product with
ether, evaporation of solvents, and chromatographic purifi-
cation on silica gel afforded the corresponding 2,3-epoxy
alcohol in a yield of 96%.
In conclusion, we have developed new chiral vanadium
catalysts for the asymmetric epoxidation of allylic alcohols,
and careful ligand modification was found to yield the
desired complexation mode of vanadium. To the best of our
i
knowledge, our catalysis, particularly the VO(OPr )3-1c
system, is the best among previously known examples of
chiral vanadium complexes with respect to selectivity.
Extension of the scope and elucidation of structure-selectiv-
ity correlations for the present catalysts will be reported in
due course.
Ack n ow led gm en t. We are grateful to Dr. S. Saito
(
Nagoya University) for helpful discussions on X-ray analy-
a
sis.
The epoxidation was conducted at -20 °C for 2-3 days in
i
toluene in the presence of VO(OPr )3 (5 mol %) and 1c (7.5 mol
b
%
), but the reaction time (entries 7-10) was 1 week. Isolated
Su p p or tin g In for m a tion Ava ila ble: Experimental proce-
c
yield. Determined by chiral HPLC (column, OD-H) analysis.
dures, characterization data for all new compounds, and X-ray data
for 1c (28 pages).
d
Determined by comparison of reported optical rotation. e Deter-
mined by chiral GLC (column, â-TA) analysis.
J O9821933
the sterically congested hydroxamic acid forms predomi-
nantly. Unlike the titanium tartrate system, molecular
sieves to sequester water, which has a deleterious effect on
both the rate and selectivity, are not required in our case.8
(
8) (a) Hanson, R. M.; Sharpless, K. B. J . Org. Chem. 1986, 51, 1922. (b)
Reference 2c.
(9) Sandararaman, P.; Barth, G.; Djerassi, C. J . Am. Chem. Soc. 1981,
103, 5004.