Claisen Condensation

Name:
Claisen Condensation
Detailed information:
A condensation reaction discovered in 1890 in which aldehydes react with esters of the type RCH₂COOR′ in the presence of metallic sodium or sodium ethylate to form unsaturated esters R″CH═C(R)COOR′. The mechanism of the reaction parallels that of acetoacetic ester condensation. An addition compound of the ester and sodium ethylate is first formed and then transformed into an unsaturated sodio ether; an addition compound between this ether and the aldehyde forms next; this changes to the unsaturated ester through a molecular rearrangement and cleavage of sodium hydroxide. Amides of alkali metals are excellent catalysts for the reaction, but they tend to form some amide by-products. Union with the carbonyl carbon takes place at the α-carbon in the acid.