Sequential Homer-Emmons

Electrolysis of diethyl phosphite in MeCN containing tetraethylammonium salts in the presence of chloroacetonitrile and aldehyde gives the corresponding a,P-unsaturated nitriles in satisfactory yields as a mixture of (E)- and (Z)-isomers, indicating that the cyanomethylphosphonate carbanion is generated then reacted during sequential Michaelis-Becker and Homer-Wadsworth-Emmons reactions. ... 

This sequential Michael and Homer-Wadsworth-Emmons reactions has been developed with a large variety of charged nucleophiles such as Uthium carbanions of phenylethynyl, methyl[(meth-ylsulfoxyl)methyl]sullide and ethyl a-(methylthio)acetate5 ° or lithium diethyl phosphite to prepare functionalized dienes, trienes, and their analogues. 

Complex molecules have also been synthesized by sequential use of the orga-nocatalytic a-amination of aldehydes by azodicarboxylates catalyzed by some of the systems shown above and by other reaction processes, such as the Passerini reaction [40], Homer-Wadsworth-Emmons olefination [41], Wittig olefination [42], and allylation reaction followed by a ring-closing metathesis [43], In addition, the combination of catalysts in cycle-specific organocascade processes [44] has allowed the synthesis of chiral complex molecules with good results. 

The sequential use of the organocatalytic a-amination of aldehydes by azodicar-boxylates with another process has provided a useful tool for the synthesis of complex molecules. Thus, the combination of the amination of linear aldehydes catalyzed by (5)-proline (20) and the Passerini reaction allowed the rapid access to norstatine based peptidomimetics albeit with low diastereoselectivities (36-98% yield, up to 4 1 dr) [27]. Moreover, the enantioselective synthesis of y-amino-a,P-unsaturated esters can be performed via the sequential a-amination-Homer-Wadsworth-Emmons olefination of aldehydes catalyzed by (5)-proline (20,10mol%) affording the expected products in high yields and enantioselectivities (85-90% yield, ee 92-99%) [28]. 

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