Cyanohydrins Michael addition

Michael addition of aromatic or heterocyclic aldehydes (via cyanohydrins) to o. unsaturated systems. Also addilion of aliphatic aldehydes catalyzed by thiazoFium yKds... 

Conversion of aldehydes to ketones via cyanohydrin derivatives (ethers) by alkylation or Michael addition also used with sdyl ethers, dialtylamlnonitnies (see also Stetter reaction). 

The potassium cyanide complex of 18-crown-6 in benzene or acetonitrile undergoes Michael addition to unsaturated carbonyl compounds (Liotta et al., 1977). In the presence of acetone cyanohydrin, the catalytic (i.e. catalytic in potassium cyanide and crown ether) cycle for hydrocyanation shown in (21)... 

Michael addition to a complexed styrene. A key step in a synthesis of 11-deoxy-anthracyclinone (3) involves the regioselective reaction of 1 with the carbanion of a protected acetaldehyde cyanohydrin to give 2 by stereospecific earo-addition. 

The classical Strecker-type synthesis involving the addition of cyanide to aldehydes, ammonolysis of the cyanohydrin, and hydrolysis of the nitrile, yields racemates. More reactive than the cyanide anion are the azolactones for aromatic aldehydes or acetamido-malonate anions for Michael additions or alkylations (Scheme 9.3.1). 

Michael addition reactions (Hetero) Diels-Alder Aldol reactions Addition of ZnR2 to RCHO Formation of cyanohydrin Cross coupling... 

Various versions of the acyl anion equivalent (32) are described by Stork etal. (use of Et2NCH2CN), Krief and co-workers (1,3-dithianes in regioselective Michael addition), Gokel et al. (use of sulphur heterocycles with thermal deblocking), Cohen and Weisenfeld" (conversion of acids into vinyl sulphides), Meyers and Campbell " (acetals derived from aryl aldehydes), and Hunig and co-workers (cyanohydrin derivatives of aryl aldehydes). 

In addition to the examples described in the previous section, various azaallyl Michael donors, successfully used in diastereoselective 1,4-additions, may be obtained by lithiation of arene acetonitriles117l llS, protected cyanohydrins 1 19 - 12 1,385, and a-amino-122 123 and a-phosphi-... 

The mechanism of the cyanide- and thioazolium ion-catalyzed conjugate addition reactions is considered to be analogous to the Lapworth mechanism for the cyanide-catalyzed benzoin condensation. Thus the cyano-stabilized carbanion resulting from deprotonation of the cyanohydrin of the aldehyde is presumed to be the actual Michael donor. After conjugate addition to the activated olefin, cyanide is eliminated to form the product and regenerate the catalyst. 

Addition of the a,3-unsaturated anion (21) to the Michael acceptor (22), in which either alkylation or 1,4-addition is possible, affords only the Michael product. Internal alkylation of the interme ate ester enolates leads to cyclopropyl derivatives (equation 7). Terpenoid polyenes are prepared through conjugate addition of the lithiat protected cyanohydrins (23) to dienyl sulfoxide (24 equation 8). ... 

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