Application of the Octacarbonyldicobalt‐Catalyzed Carbonylation of Ethyl Diazoacetate for the One‐Pot Synthesis of N ‐ tert ‐Butyl‐ trans ‐α‐ethoxycarbonyl‐β‐phenyl‐β‐lactam

N ‐ tert ‐Butyl‐ trans ‐α‐ethoxycarbonyl‐β‐phenyl‐β‐lactam has been prepared in 95 % yield (GC) by the octacarbonyldicobalt‐catalyzed carbonylation of ethyl diazoacetate in dichloromethane in the presence of N ‐ tert ‐butylbenzaldimine at 10 °C and 75 bar pressure of carbon monoxide. The key step of the reaction is the catalytic formation of the highly reactive (ethoxycarbonyl)ketene from both of the intermediary complexes [Co 2 (CO) 7 (CHCO 2 Et)] and [Co 2 (CO) 6 (CHCO 2 Et) 2 ], which is in situ scavenged by the imine in a [2+2] cycloaddition reaction. DFT (PBEPBE/6‐31G**) calculations revealed that the reaction follows a two‐step mechanism via a noncyclic intermediate with a reaction free energy of –15.9 kcal/mol and a free‐energy barrier of 24.7 kcal/mol for the second rate‐limiting step. The computation also shows that the formation of the trans isomer is preferred both kinetically and thermodynamically. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)