Acyclic Stereoselection. 22. Diastereofacial Selectivity in the Lewis Acid Mediated Reactions of Allylsilanes with Chiral Aldehydes and Enones

Article abstract of DOI:10.1021/jo00196a022

The Lewis acid mediated reactions of chiral aldehydes 1-4 and enones 5-8 with allylsilanes 9 and 10 have been investigated.With aldehyde 1 and enones 5-7, modest diastereofacial preferences are seen, in the sense predicted by application of Felkin's model for asymmetric induction.Aldehydes 2-4 and enone 8 appear to react by way of chelated intermediates.With these four compounds, the diastereofacial preferences are rather large and are in the sense that is consistend with attack of the allylsilane on the least hindered face of the chelated intermediate.In the reaction of the trans and cis enones 6 and 8 with allyltrimethylsilane, a dramatic reversal of diastereofacial preference is observed; enone 6 gives a 84:14 ratio of products, while enone 8 provides a 10:90 mixture of the same products.