Still-Gennari olefination diastereoselectivity

Fig. 11.15. Analysis of the overall stereoselectivity of a Still—Gennari olefination such as the one in Figure 11.13 simple diastereoselectivity of the formation of the alkoxide intermediate from the achiral phosphonate A and the achiral aldehyde B. For both reagents the terms "back face" and "front face" refer to the selected projection.

Fig. 11.16. Analysis of the simple diastereoselectivity of a Still-Gennari olefination that starts from the enantiomeri-cally pure phosphonate A and the achiral aldehyde B.

We now analyze the Still-Gennari olefination of Figure 9.18. The reagents there are the enantiomerically pure chiral phosphonate A, with which you are familiar from Figure 9.17, and an enantiomerically pure a-chiral aldehyde B. The diastereoselectivity of the formation of the crucial alkoxide intermediate(s) is in this case determined by the interplay of three factors ... 

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