Z-selective synthesis of alpha,beta-unsaturated amides with triphenylsilylacetamides

With the purpose of developing a method of preparing Z-alpha,beta-unsaturated amides, the Peterson reaction of the (triphenylsilyl)acetamide Ph(3)SiCH(2)COX (1, X = NBn(2); 3, X = NMe(2)) with various aldehydes was examined. The reaction of aromatic aldehydes gave selectivities up to >97:3. It was found that the selectivity was a function of the electronic nature of the aromatic ring and higher Z selectivity was attained with electron-rich aldehydes. With aliphatic aldehydes selectivities up to 92:8 were achieved, and unlike with analogous phosphorus reagents, less sterically hindered aldehydes gave higher Z selectivity. Also, 3, which has a smaller amide group than 1, tended to give rise to higher selectivity. A comparison with the reaction of trimethylsilyl analogues revealed the significance of the phenyl substituents on the silyl group.