P-aryl-substituted nitroalkenes

Michael additions are among the most important organocatalytic transformations.The ability of prolinol silyl ethers to form enamines, diena-mines, trienamines or iminium ions makes them appealing in a number of chemical transformations based on addition of a nucleophile to an a,p-unsaturated carbonyl compound or other Michael acceptor. The first example of Michael addition catalysed by a prolinol silyl ether was published by Hayashi and coworkers. Aliphatic aldehydes added to a range of aryl-substituted nitroalkenes. Prolinol silyl ether Cla presumably formed chiral enamines with aldehydes. The F-anh-enamine was formed and it reacted with nitroalkene via an acyclic synclinal transition state, originally proposed... 

The addition of Grignard reagents or organolithiums (alkenyl, alkyl, alkynyl, allyl or aryl) to nitroenamines (281)213 was reported by Severin to afford P-substituted-a-nitroalkenes.214 b Similarly, ketone enolates (sodium or potassium), ester enolates (lithium) and lactone enolates (lithium) react to afford acr-nitroethylidene salts (294) which, on hydrolysis with either silica gel or dilute acid, afford 7-keto-a,(3-unsaturated esters or ketones (295)2l4c-d or acylidene lactones (296).214 Alternatively, the salts (294, X s CH2) can be converted to -y-ketoketones (297) with ascorbic acid and copper catalyst. 

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