Ab initio study on the mechanism of cycloaddition reaction of ketene with methylenimine: A new reaction scheme

The cycloaddition reaction of ketene and methylenimine, leading to 2‐azetidinone, has been studied theoretically by RHF /3‐21 G and IRC. This reaction is believed to be nonsynchronous and concerted, taking place through a twisted transition state. Four π orbitals are involved in this reaction, which is a “2 × [1 + 1]”‐type cycloaddition. In the course of the reaction, rotation of the methylene group instead of oxygen in ketene was ascertained. The activated barrier is calculated to be 33.9 kcal/mol.