In this section we will see examples of cyclizations that take place through intermediates of radical type, carbene or nitrene.

A) We begin with a radical cyclization, which uses tributyltin hydride as a reagent and is initiated by AIBN

aibn cycling


1. initiation

cyclization aibn initiation

2. Propagation

cyclization aibn propagation

B) In this second example we will take advantage of the reactivity of the nitrenes through the carbon-nitrogen insertion to obtain the carbazole.

carbazole synthesis


carbazole synthesis mechanism

C) Synthesis of indole from azide, via nitrene.

indole synthesis via nitrene


indole synthesis via nitrene mechanism

D) Cyclization processes via carbenes

synthesis via carbenes


synthesis via carbenes mechanism