Stereodivergence in the Ireland–Claisen Rearrangement of α‑Alkoxy Esters

A systematic investigation into the Ireland–Claisen rearrangement of α-alkoxy esters is reported. In all cases, the use of KN­(SiMe3)2 in toluene gave rearrangement products corresponding to a Z-enolate intermediate with excellent diastereoselectivity, presumably because of chelation control. On the other hand, chelation-controlled enolate formation could be overcome for most substrates through the use of lithium diisopropylamide (LDA) in tetrahydrofuran (THF).