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 [N 2 CHCONR 2 , NR 2 =NEt 2 ( 3a ), NBu 2 ( 3b ), N( i‐ Pr) 2 ( 3c ), N(CH 2 Ph) 2 ( 3d ), N( i‐ Pr)(CH 2 Ph) ( 3e )], was investigated using as catalysts dinuclear Ru(I,I) complexes of the type [Ru 2 (μ‐L 1 ) 2 (CO) 4 L 2 2 ], where L 1 is a bidentate bridging acetate, calix[4]arenedicarboxylate, saccharinate, pyridin‐2‐olate, or triazenide ligand, as well as [RuCl 2 ( 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 , [Ru 2 (μ‐sac) 2 (CO) 5 ] 2 (sa c =saccharinate) and [Ru 2 (μ‐6‐chloropyridin‐2‐olate) 2 (CH 3 CN) 2 (CO) 4 ] are as effective as Rh 2 (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.