Cyclization of carbenes nitrenes and radicals

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

Mechanism:

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

Mechanism:

carbazole synthesis mechanism

C) Synthesis of indole from azide, via nitrene.

indole synthesis via nitrene

Mechanism:

indole synthesis via nitrene mechanism

D) Cyclization processes via carbenes

synthesis via carbenes

Mechanism:

synthesis via carbenes mechanism