Powerful Ti-Crossed Claisen Condensation between Ketene Silyl Acetals or Thioacetals and Acid Chlorides or Acids

A powerful Ti-crossed Claisen condensation between ketene silyl acetals (KSAs) and acid chlorides was successfully performed to give α-monoalkylated esters and thermodynamically unfavorable (less accessible) α,α-dialkylated β-keto esters in good yield (46 examples; 41−98% yield). A closely related reaction between ketene silyl thioacetals (KSTAs) and acid chlorides also proceeded smoothly to give α-monoalkylated and α,α-dialkylated β-keto thioesters (21 examples; 61−97% yield). The present protocol was extended to the direct condensation of KSAs with carboxylic acids (14 examples; 71−97% yield).