Allyl organometallic compounds 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... 

Amino aldehydes provide useful starting materials for the sequence of Scheme 11.3 because they can easily be prepared from a-amino acids in enantiomerically pure forms and are, therefore, useful chiral building blocks.18 The addition of organometallic allylic reagents (including Zn, used in the reaction described) to such compounds can produce homoallylic alcohols 13 with a high anh-diastereoselectivity. 

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