Ruthenium catalysts for carbenoid intramolecular C-H insertion of 2-diazoacetoacetamides and diazomalonic ester amides

The intramolecular carbenoid C-H insertion of 2-diazoacetoacetamides, leading to γ- and/or β-lactams, is catalyzed effectively by dinuclear Ru(I,I) complexes of the type Ru₂(μ-L¹)₂(CO)₄L²₂], where L¹ is a bidentate bridging acetate, calix4]arenedicarboxylate, saccharinate or 6-chloropyridin-2-olate ligand. By comparison with rhodium catalysts, namely dirhodium tetraacetate and dirhodium calix4]arenedicarboxylate complexes, product yields are similarly high and the regioselectivity of the insertion reaction is the same. Surprisingly, even the ruthenium(0) cluster Ru₃(CO)₁₂ was found to be an effective catalyst for carbenoid C-H insertion of 2-diazoacetoacetamides and also of some diazoacetamides. In terms of diastereoselectivity, trans-isomers of β- and γ-lactams are obtained. However, the β-lactam obtained from diazomalonic ester amide 2 yields the cis-isomer stereoselectively, which slowly rearranges to the trans-isomer.