References and Notes
<A NAME="RG25908ST-1A">1a</A>
Katsuki T. In Comprehensive
Asymmetric Catalysis
Vol. 2:
Jacobsen EN.
Pfaltz A.
Yamamoto H.
Springer;
Heidelberg:
1999.
p.621-648
<A NAME="RG25908ST-1B">1b</A>
Jacobsen EN.
Wu MH. In Comprehensive Asymmetric Catalysis
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2:
Jacobsen EN.
Pfaltz A.
Yamamoto H.
Springer;
Heidelberg:
1999.
p.649-677
<A NAME="RG25908ST-1C">1c</A>
Johnson RA.
Sharpless KB. In Catalytic Asymmetric Synthesis
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ed.:
Ojima I.
Wiley-VCH;
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2000.
p.231-285
<A NAME="RG25908ST-1D">1d</A>
Katsuki T. In Catalytic Asymmetric Synthesis
2nd
ed.:
Ojima I.
Wiley-VCH;
New
York:
2000.
p.287-325
<A NAME="RG25908ST-2">2</A>
Aziridines
and Epoxides in Organic Synthesis
Yudin AK.
Wiley-VCH;
Weinheim:
2006.
See, for example:
<A NAME="RG25908ST-3A">3a</A>
Pericàs MA.
Puigjaner C.
Riera A.
Vidal-Ferran A.
Gómez M.
Jimenez F.
Muller G.
Rocamora M.
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<A NAME="RG25908ST-3B">3b</A>
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Puigjaner C.
Gómez M.
Benet-Buchholz J.
Vidal-Ferran A.
Pericàs MA.
Adv. Synth.
Catal.
2007,
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2265 ;
and references cited therein
For leading references on this transformation,
see:
<A NAME="RG25908ST-4A">4a</A>
Frohn M.
Shi Y.
Synthesis
2000,
1979
<A NAME="RG25908ST-4B">4b</A>
Shi Y.
Acc.
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<A NAME="RG25908ST-4C">4c</A>
Hickey M.
Goeddel D.
Crane Z.
Shi Y.
Proc. Natl. Acad. Sci. U.S.A.
2004,
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<A NAME="RG25908ST-4D">4d</A>
Yang D.
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<A NAME="RG25908ST-4E">4e</A>
Xia QH.
Ge HQ.
Ye CP.
Liu ZM.
Su KX.
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1603
<A NAME="RG25908ST-5">5</A>
Wang Z.-X.
Tu Y.
Frohn M.
Zhang J.-R.
Shi Y.
J. Am. Chem.
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and references cited therein
<A NAME="RG25908ST-6">6</A>
Wu XY.
She X.
Shi Y.
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2002,
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8792
<A NAME="RG25908ST-7">7</A>
Nieto N.
Molas P.
Benet-Buchholz J.
Vidal-Ferran A.
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<A NAME="RG25908ST-8">8</A>
Diacetate 2 is
a very effective as epoxidation catalyst using 10 mol% of
catalyst loading. Loading for Shi’s catalysts usually ranges
from 20 mol% to 30 mol%. See refs. 4a-c.
<A NAME="RG25908ST-9">9</A>
Singleton DA.
Wang Z.
J. Am. Chem. Soc.
2005,
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Nieto N.
Munslow IJ.
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<A NAME="RG25908ST-11">11</A>
Compound 4e (0.37
g, 46% yield) was obtained as a colourless oil. ¹H
NMR (400 MHz, CDCl3): δ = 7.27-7.40 (m,
15 H), 6.48 (dt, 1 H, J = 16.0,
1.3 Hz), 6.28 (dt, 1 H, J = 16.0,
6.9 Hz), 5.42 (s, 1 H), 3.62 (t, 2 H, J = 6.9
Hz), 2.60 (qd, 2 H, J = 6.9,
1.3 Hz). ¹³C NMR: δ = 142.4,
137.7, 131.6, 128.5, 128.4, 127.4, 127.3, 127.2, 127.0, 126.0, 83.7,
68.7, 33.6.
The asymmetric epoxidation of alkene 4e to give (+)-5e was carried
out by the general procedure (see ref. 12).
Compound
5e (0.15 g, 52% yield); white solid; mp 56 ˚C; [α]D
²5 +28.53
(c 0.12, CH2Cl2).
IR: 2871-3066, 1599, 1491, 1097, 1037, 855 cm-¹. ¹H
NMR (400 MHz, CDCl3): δ = 7.12-7.36
(m, 15 H), 5.36 (s, 1 H), 3.69 (d, 1 H, J = 1.9
Hz), 3.65 (t, 2 H, J = 6.0 Hz),
3.13 (td, J = 5.6, 1.9 Hz),
2.02 (td, 2 H, J = 5.6, 6.0
Hz). ¹³C NMR: δ = 142.3,
142.3, 137.8, 128.6, 128.5, 128.2, 127.6, 127.6, 127.3, 127.1, 127.0, 125.7,
84.0, 65.7, 61.1, 58.8, 33.1. HRMS: m/z calcd for C23H22O2Na:
353.1517; found: 353.1520. Enantiomeric excess was determined by
HPLC using a chiral stationary phase (Chiracel OD-H column), eluent:
hexane-i-PrOH (95:5); flow:
0.8 mL/min; l = 216 nm; t
R (major) = 10.8
min; t
R (minor) = 11.7
min.
<A NAME="RG25908ST-12">12</A>
General Procedure
for the Epoxidation of Alkenes: The corresponding alkene (2.22
mmol) and the required amount of catalyst 3 (10-30
mol%) were dissolved in MeCN-dimethoxymethane
(44 mL, 1:2). A pH 6 buffer solution (8 mL), tetrabutylammonium
hydrogen sulfate (35 mg, 0.10 mmol) was slowly added with stirring
and the mixture was cooled to the desired temperature. The flask
was equipped with two syringe pumps; one of them was filled with
a solution of Oxone (3.62-6.82 mmol) in pH 6 buffer (14
mL) and the other one with a solution of K2CO3 (5.33-16.06 mmol)
in H2O (14 mL). The two solutions were added dropwise
over a 2 h period (syringe pump). The solution was stirred at 0 ˚C
for the corresponding reaction time. The mixture was diluted with
H2O (40 mL) and extracted with the appropriate organic
solvent [5a and 5h:
hexane (4 × 40 mL); 5b-g,i-l: CH2Cl2 (4 × 40
mL)]. The combined organic fractions were collected and
washed with brine (50 mL), dried over Na2SO4,
filtered and the solvents were removed under reduced pressure. The
crude material was purified by flash chromatography on SiO2˙Et3N
(2.5%). Enantioselec-tivity was
determined by chiral chromatography and the configuration of epoxides
was established by comparison with either reported elution order
or optical rotation if reported data was available. For 5a, HPLC; Chiralpak AD.¹4 For 5b,¹5 5j,¹6 and 5k,¹7 GC: gamma dex.
For 5c
¹8 and 5h,¹9 HPLC; Chiralcel
OD. For 5d, HPLC; Chiralcel OD-H.²0 For 5f,²¹ HPLC:
Chiralcel AD-H. For 5l GC: gamma dex.
<A NAME="RG25908ST-13">13</A> Higher pH values were not considered
since the background reaction could be significant. See:
Kurihara M.
Ito S.
Tsutsumi N.
Miyata N.
Tetrahedron Lett.
1994,
35:
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Poignant G.
Catalysis
for Fine Chemical Synthesis: Hydrolysis, Oxidation and Reduction
1st
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John Wiley & Sons;
Chichester:
2002.
p.94-98
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Wang Z.-X.
Tu Y.
Frohn M.
Zhang J.-R.
Shi Y.
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