Diruthenium(I,I) Catalysts for the Formation of β‐ and γ‐Lactams via Carbenoid C ? H Insertion of α‐Diazoacetamides

Intramolecular carbenoid CH insertion of five α-diazoacetamides [N2CHCONR2, NR2=NEt2 (3a), NBu2 (3b), N(i-Pr)2 (3c), N(CH2Ph)2 (3d), N(i-Pr)(CH2Ph) (3e)], was investigated using as catalysts 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, pyridin-2-olate, or triazenide ligand, as well as [RuCl2(p-cymene)]2. The Ru(I,I) complexes were found to be suitable catalysts for the carbenoid cyclization reactions, except in the case of 3a. With diazoamides 3b–e, [Ru2(μ-sac)2(CO)5]2 (sac=saccharinate) and [Ru2(μ-6-chloropyridin-2-olate)2(CH3CN)2(CO)4] are as effective as Rh2(OAc)4 under the same conditions, although some differences in the regioselectivity and chemoselectivity of the cyclization are observed. The carbenoid cyclization reactions yield γ-lactams from diazoamides 3a and 3b, both a β- and a γ-lactam from 3c, and a β-lactam as well as a 3-azabicyclo[5.3.0]deca-5,7,9-trien-2-one from 3d. With 3e, formation of γ-lactam 21 and of bicyclic lactam 23 prevails.