Interaction of β-Lactam Carbenes with 3,6-Diphenyltetrazines: A Five-Step Cascade Reaction for the Direct Construction of Indeno[2,1-<i>b</i>]pyrrol-2-ones

A study of the nucleophilic addition of β-lactam carbenes to 3,6-diphenyltetrazines is reported. Instead of the formation of pyrazole derivatives like most reactions between nucleophilic or ambiphilic carbenes and 3,6-disubstituted tetrazines, β-lactam carbenes reacted with 3,6-diphenyltetrazines to produce indeno[2,1-<i>b</i>]pyrrol-2-ones in good yields. The reaction proceeds most probably through a five-step cascade process. This work has not only provided a one-pot operation for the efficient construction of mutisubstituted indeno[2,1-<i>b</i>]pyrrol-2-ones but also revealed the nucleophilicity of β-lactam carbenes.