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

Intramolecular carbenoid CH insertion of five α‐diazoacetamides [N2CHCONR2, 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.