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DOI: 10.1055/s-2008-1077901
SimplePhos as Efficient Ligand for the Copper-Catalyzed Kinetic Resolution of Cyclic Vinyloxiranes with Grignard Reagents
Publikationsverlauf
Publikationsdatum:
02. Juli 2008 (online)
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Abstract
Cyclic vinyloxiranes react with Grignard reagents under copper catalysis. Highly efficient kinetic resolution is achieved with the new SimplePhos family of chiral phosphorus ligands. Stereodivergence could be exploited to get either the SN2 or SN2′ product with up to 96% ee.
Key words
epoxides - asymmetric synthesis - Grignard reagents - catalysis - copper
- 1
Modern
Organocopper Chemistry
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References and Notes
Typical Procedure
In
a dried Schlenk tube under N2 atmosphere were placed CuTC
(5.7 mg, 0.03 mmol) and (S,S)-L1 (13.5
mg, 0.03 mmol). Then, CH2Cl2 was added (6
mL) and the mixture was stirred at r.t. for 20 min. The tube was
cooled down to -78 ˚C and 1,3-cyclohexadiene
monoepoxide 1 (100 µL, 1 mmol) was added. c-HexMgCl
(250 µL, 2.0 M in Et2O, 0.5 mmol) was added
dropwise over a period of 3 min. The reaction was stirred for 3
h and quenched with MeOH and (NH4)2SO4 before
being allowed to reach r.t. The aqueous phase was extracted with
CH2Cl2 and the organic layer was dried over MgSO4 and
the solvent removed on rotary evaporator (55% conversion,
88% ee). The crude product was purified by flash chromatography
on SiO2 (pentane then pentane-Et2O, 75:25)
yielding 79 mg (44% yield) of a white solid. [α]D
²0
-128.2
(c 0.87, CHCl3, ee = 88%). ¹H
NMR (400 MHz, CDCl3): δ = 5.68 (m,
2 H), 4.20 (br, 1 H), 2.09 (m, 1 H), 1.97 (m, 1 H), 1.74-1.60
(m, 6 H), 1.45-1.35 (m, 3 H), 1.22-1.12 (m, 4
H), 1.07-0.97 (m, 2 H). ¹³C
NMR (100 MHz, CDCl3): δ = 133.3, 130.1,
67.5, 42.4, 41.1, 32.7, 30.2, 29.7, 26.7, 23.7.