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 ZV-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(CHCO2Et)] and [Co2(CO) 6(CITCO2Et)2], which is in situ scavenged by the imine in a [2+2] cycloaddition reaction. DPT (PBEPBE/6-31G **) calculations revealed that the reaction follows a two-step mechanism via a noncydic 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 thermodynamicaily.
- C-C coupling
- Carbene ligands
- Carbonyl ligands
- Density functional calculations
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Organic Chemistry