SolutionsFacial control by the enolate
Exercise 1
A chiral aldehyde gives a 4:1 diastereomer ratio with an achiral enolate, and a chiral enolate gives a 10:1 ratio with an achiral aldehyde. What selectivity can roughly be expected in the matched and mismatched pairs?
As a first approximation the preferences multiply: in the matched pair, about 4 × 10 = 40:1; in the mismatched pair, 10/4 ≈ 2.5:1 in favour of the product preferred by the enolate, the more selective component. In practice the values deviate from this estimate, but the trend holds.