The Kowalski ester homologation is a chemical reaction for the homologation of esters.
This reaction was designed as a safer alternative to the Arndt–Eistert synthesis, avoiding the need for diazomethane. The Kowalski reaction is named after its inventor, Conrad J. Kowalski.
Reaction mechanism
The mechanism is disputed. One proposal:
Enolate formation: Ester is deprotonated at the α-position, to give enolate anion. CH₂ insertion: Enolate reacts with dihalomethane, to introduce a –CH2– group. Rearrangement and stabilization Under basic conditions, a homologated ester forms.
Variations
By changing the reagent in the second step of the reaction, the Kowalski ester homologation can also be used for the preparation of silyl ynol ethers.
See also Curtius rearrangement
References