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3. Experimental section
2b (R=Cl)1a and 2c (R=Br)1b were prepared according to literature procedures.
3.1. 3,30,5,50Tetraterbutyl-2,20-biphenol,8 2d
Under an inert atmosphere, BIPOL (3 g) was dissolved in 100 ml of tert-butyl-methylether. SnCl4 (20
ml) was added, and the solution was stirred at 20°C for 50 h. Water (50 ml) was added to quench the
reaction, and the product was extracted with dichloromethane (2×100 ml). The product 4d was obtained
in pure form after recrystallization first from ethanol–water, then from toluene (1.5g, 25% yield).
3.2. Ene-reaction, general procedure
Under an atmosphere of argon, (R)-BINOL 1 (0.05 mmol) and Ti(OiPrO)4 (0.05 mmol) were stirred
in dry toluene (2 ml) at 20°C for 30 min. At 0°C, 2 (0.05 mmol) was added, immediately followed by a
mixture of α-methyl-styrene (0.5 mmol) and the alkyl glyoxylate (0.5 mmol, distilled immediately before
use), in 2 ml of toluene. After stirring at 0°C for the indicated time, and standard aqueous work-up (brine,
extraction in ethyl acetate, acidic washing), the adduct was isolated by chromatography on silica (ethyl
acetate:pentane=15:85).
Enantiomeric excesses were determined by HPLC analysis (Daicel Chiralpak AD,
cyclohexane:iPrOH=99:1). The absolute configuration of the homoallylic alcohol is (R), based on
literature data.1e We checked the optical rotation for run 6, [α]20=−22.2 (c=1.9, chloroform).
D
Acknowledgements
We gratefully thank Dr. V. Delogu (University of Sassari, Italy) for fruitful discussions.
References
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5. We could not improve the yields, either by use of 10 equivalents of α-methyl-styrene or by slow introduction of the
n-butyl-glyoxylate.
6. Catalyst BINOL–TiCl2, Ref. 3d.
7. Program Insight II® 97.0, force field esff, ε=1 (vacuum).
8. Models of the complexes of butyl glyoxylates and the other isomers A–G were also minimized. The structure F seems
to favor the formation of the (R)-homoallylic alcohol. All 3D models are available on the Web: http//www-ledss.ujf-
grenoble.fr/WebSrv/poster.html