Figure 1.

Scope II: Various diazene/aldehyde combinations.^[a] [a] Unless noted otherwise, the reactions were performed on a 0.40 mmol scale with 10 mol % Me₃SiONa in THF at room temperature. [b] Me₃SiOK instead of Me₃SiONa. [c] Formed along with the corresponding silyl enol ether in 30 % yield. [d] Yield determined by NMR spectroscopy using CH₂Br₂ as an internal standard. [e] The reaction was performed on a 1.8 mmol scale with 5.0 mol % Me₃SiONa in THF at room temperature.