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, calix[4]arenedicarboxylate, saccharinate or 6-chloropyridin-2-olate ligand. By comparison with rhodium catalysts, namely dirhodium tetraacetate and dirhodium calix[4]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.