Conjugate addition aldehydes with cyanide

The Stetter Reaction is a 1,4-addition (conjugate addition) of an aldehyde to an a,p-unsaturated compound, catalyzed by cyanide or a thiazolium salt. This reaction competes with the corresponding 1,2-addition, which is the Benzoin Condensation. However, the Benzoin-Condensation is reversible, and since the Stetter Reaction leads to more stable products, the main product will be derived from 1,4-addition. 

The Michael-type addition, a nucleophilic addition of an anion to the carbon-carbon double bond of an a,(3-unsaturated ketone, aldehyde, nitrile, nitro, sulphonyl, or carboxylic acid derivative, provides a powerful tool for carbon-carbon bond formation. The reaction is most successful with relatively nonbasic ( soft ) nucleophiles such as thiols, cyanide, primary and secondary amines, and P-dicarbonyl compounds. There is often a competition between direct attack on the carbonyl carbon (1,2-addition) and conjugate addition (1,4-addition) when the substrate is an a,(3-unsaturated carbonyl compound. 

Treatment of a conjugated aldehyde or ketone with cyanide in the presence of acid may result in attack by cyanide at the jS-carbon, in contrast with cyanohydrin formation (Section 17-11). This transformation proceeds through a 1,4-addition pathway. The reaction includes protonation of the oxygen, then nucleophilic j8-attack, and finally enol-keto tautomerization. 

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