Intramolecular Fischer Indole synthesis and its combination with an aromatic [3,3]-sigmatropic rearrangement for the preparation of tricyclic benzo[cd]indoles

Abstract

Aryl hydrazides that contain a latent carbonyl group that is tethered to the para position of the aromatic ring undergo the Fischer indolization reaction in an intramolecular fashion. Strategic insertion of a C-C double bond in the tether enabled the indole product to form tricyclic benzo-[cd]indoles in good overall yield by an aromatic [3,3] sigmatropic rearrangement reaction. This intramolecular Fischer indole synthesis may find further applications in the areas of related natural product syntheses, as well as pharmaceutical and materials sciences.|Aryl hydrazides containing a latent carbonyl group undergo the Fischer indolization reaction in an intramolecular fashion, when tethered to the para position of the aromatic ring. Strategic insertion of a C-C triple bond in the tether, enabled the indole products to go through an aromatic [3,3] sigmatropic rearrangement reaction, affording multicyclic chromeno-indoles. The tandem process can be interrupted at the indolophane stage for the separate thermal ortho-Claisen rearrangement, if the double bond migration needs to be prevented. This intramolecular Fischer indolization process may find further applications in the areas of related natural product synthesis and materials sciences.; Aryl hydrazides containing a latent carbonyl group undergo the Fischer indolization reaction in an intramolecular fashion, when tethered to the para position of the aromatic ring. Strategic insertion of a C-C triple bond in the tether, enabled the indole products to go through an aromatic [3,3] sigmatropic rearrangement reaction, affording multicyclic chromeno-indoles. The tandem process can be interrupted at the indolophane stage for the separate thermal ortho-Claisen rearrangement, if the double bond migration needs to be prevented. This intramolecular Fischer indolization process may find further applications in the areas of related natural product synthesis and materials sciences.