Enones reaction with cyanide

The very first conjugate addition reaction in this chapter depended on the conditions of the reaction. Treating an enone with cyanide and an acid catalyst at low temperature gives a cyanohydrin by direct attack at C-O, while heating the reaction mixture leads to conjugate addition. What is going on ... 

The C-1 phosphate has been drawn in a position hydrogen-bonded with an arginine residue. The iminium ion is sufficiently exposed to solvent so that borohydride, cyanide or tetranitromethane [58] reactions with the bound substrate are possible. A thiol group has been drawn in a position where the enone phosphate inhibitor could react with it. 

The synthesis started with the known hydrindenone derivative, 154 (Scheme 15) (177). Surprisingly, the group transformation of the secondary alcohol to the cyanide 155 via the tosylate occurred under retention of configuration in 64% yield. The authors were able to exclude a retroaldol-aldol reaction sequence as the reason for the unusual stereochemistry but did not further elaborate. To form the annelated pyrrolidinone, the enone was chemo- and stereoselectively reduced by... 

The (chloromethyl)furan (45) gives mainly the butenolide (46) on treatment with aqueous potassium cyanide.A detailed study of the reaction of furfural with primary aromatic amines has shown that 2,4-di(arylamino)cyclopent-2-enones (47) are usually formed intermediate 4,5-di(arylamino)cyclopent-2-en-ones (48) are occasionally isolated.The zinc-chloride-induced rearrangement of the 2-furyl alcohols (49 R = Bu, allyl, or Ph) to the cyclopentenolones (51) is thought to involve the cations (50) as key intermediates. The enolate that is formed by the action of butyl-lithium on 2-benzylfuran has been isolated... 

We ll consider the low-temperature reaction first. As you know from Chapter 6, it is quite normal for cyanide to react with a ketone under these conditions to form a cyanohydrin. You also know from Chapter 6 that cyanohydrin formation is reversible. Even if the equilibrium for cyanohydrin formation lies well over to the side of the products, there will always be a small amount of starting enone remaining. Most of the time, this enone will react to form more cyanohydrin and, as it does, some cyanohydrin will decompose back to enone plus cyanide—such is the nature of a dynamic equilibrium. But every now and then—at a much slower rate—the starting enone will undergo a conjugate addition with the cyanide. 

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