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 ...