Diastereoface differentiation in addition of lithium enolates to chiral α,β-epoxyaldehydes

The aldolisation reaction of lithium ester enolates with chiral α,β-epoxyaldehydes 2a–2f has been investigated. The reaction proceeds with diastereofacial preference in favour of the anti isomer (anti:syn ≈ 4:1) and can be greatly enhanced in the case of cis α,β-epoxy-aldehydes 2a–2c by a synergic effect of temperature and enolate excess (anti:syn 13:1). The Felkin-Ahn model can explain the results obtained on asymmetric induction.