Organic syntheses via transition-metal complexes.: 119.: α-Methylenation and α-alkenylation of α,β-unsaturated amides by means of carbene tungsten complexes:: A novel Baylis-Hillman type reaction

Fischer carbene complexes were found to undergo Baylis-Hillman type additions to alpha,beta-unsaturated acid amides. Reactions of (non-CH-acidic) carbene tungsten complexes la-c with (CH-acidic) but-2-enoic acid amides 2 in the presence of POCl3/Et3N resulted in an alpha-addition of the carbene ligand to the amide backbone and formation of cross-conjugated aminocarbene complexes 3. Reaction of CH-acidic carbene tungsten complexes 1d-h gave the cross-conjugated aminocarbene complexes 9 (which are double-bond isomers of compounds 3) together with (cyclobutenyl)carbene complexes 10, by alpha- and beta-addition, respectively, to the but-2-enoic amides 2. Compounds 9 and 10 are valence isomers, but they do not interconvert thermally.