Allyl organometallic compounds relative diastereoselectivity

We have seen in Section 1.1.3 that reactions of many allyl organometallics and chiral C=X electrophiles proceed with only modest levels of relative diastereoselection. Significant improvement in dia-stereoselectivity is possible, however, by using double asymmetric synthesis, that is, by using the highly enantioselective allyl metal reagents described in Section 1.1.4 rather than the less diastereoface-selec-tive achiral allyl metal compounds discussed in Section 1.1.3. Double asymmetric synthesis is also... 

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