Isopropyl cation chiral

A number of other types of chiral auxiliaries have been employed in enolate alkylation. Excellent results are obtained using amides of pseudoephedrine. Alkylation occurs anti to the a-oxybenzyl group.93 The reactions involve the Z-enolate and there is likely bridging between the two lithium cations, perhaps by di-(isopropyl)amine.94... 

The stereochemistry of these steps is of course controlled by the original chiral centre derived from malic acid. The acetate prefers to adopt a pseudo-equatorial position in the cation 105 and the conformational drawings 105a-107a show that a chair conformation for the [3,3] step with equatorial substituents gives the first two new chiral centres and a pseudo-equatorial position for the isopropyl substituent in the ionic cyclisation gives the third. 

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