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L. Bohꢀe, M. Kammoun / Tetrahedron Letters 45 (2004) 747–751
Table 2. Epoxidation of olefins using iminium salt 2d as catalysta
Entry
Olefin
Catalyst loading (mol %)
Time (h)b
Conversion (%)c
1
12
13
14
15
16
17
18
19
20
21
22
10
10
10
10
5
6
6
6
6
2
4
4
4
2
6
2
92
85
2
3
89
85
4
5
100
100d
100
100e
100
100
100f
6
5
7
5
8
5
9
5
10
11
5
5
a Reaction conditions: molar ratio olefin/KHSO5/NaCO3H ¼ 1:2:4, CH3CN–H2O (3%), rt.
b Reactions monitored by TLC and/or 1H NMR spectroscopy.
c Conversion to the epoxide determined by 1H NMR analysis of the crude product integrating the epoxide versus unchanged olefin.
d Exclusively exocyclic epoxide, 1:1 mixture of diastereoisomers (ratio determined by 1H NMR spectroscopy).
e Molar ratio syn:anti ¼ 1:3.8 determined by 1H NMR spectroscopy.
f Using CH3CN/dioxane (1:1)-H2O (3%) as solvent, molar ratio a=b ¼ 1:3.3 determined by 1H NMR spectroscopy.
Rassias, G. A.; Barros, D.; Bethell, D.; Schilling, M. B. J.
a-preference in the peracid epoxidation of this
Chem. Soc., Perkin Trans. 1 2000, 3325–3334; (c) Page, P.
substrate,28 thus suggesting that factors stronger than
C. B.; Rassias, G. A.; Barros, D.; Ardakani, A.; Buckley,
B.; Bethell, D.; Smith, T. A. D.; Slawin, M. A. Z. J. Org.
govern the stereochemistry of the oxaziridinium 1d-
the steric interactions during the reagentÕs approach
Chem. 2001, 66, 6926–6931; (d) Page, P. C. B.; Rassias, G.
mediated epoxidation of this more substituted double
A.; Barros, D.; Ardakani, A.; Bethell, D.; Merifield, E.
bond.
Synlett 2002, 580–582.
9. (a) Armstrong, A.; Ahmed, G.; Garnett, I.; Goacolou, K.
In conclusion, we have developed a highly efficient
dihydroisoquinolinium-derived catalyst for the oxaz-
iridinium-mediated epoxidation of olefins by Oxoneꢀ.
This iminium salt 2d, an easily prepared and handled
crystalline solid, not only improves the epoxidation of
di- and more substituted olefins but also seems well
suited for the efficient catalytic epoxidation of
Synlett 1997, 1075–1076; (b) Armstrong, A.; Ahmed, G.;
Garnett, I.; Goacolou, K.; Wailes, J. S. Tetrahedron 1999,
55, 2341–2352.
10. Minakata, S.; Takemiya, A.; Nakamura, K.; Ryu, I.;
Komatsu, M. Synlett 2000, 1810–1812.
11. Wong, M.-K.; Ho, L.-M.; Zheng, Y.-S.; Ho, C.-Y.; Yang,
D. Org. Lett. 2001, 3, 2587–2590.
12. Lacour, J.; Monchaud, D.; Marsol, C. Tetrahedron Lett.
2002, 43, 8257–8260.
monosubstituted olefins thus enlarging, from
a
practical standpoint, the scope of this methodology.
Experimental work to confirm this point is underway.
ꢀ
13. Poisson, D.; Cure, G.; Solladie, G.; Hanquet, G. Tetra-
hedron Lett. 2001, 42, 3745–3748.
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ꢀ
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