Pentaleno[1,2-c]pyrroles: Tricyclic 5/5/5 Fused Rings

A novel method for the preparation of tetrahydropentaleno[1,2-c]pyrroles (8) is described via the reaction of anilines with 1-en-4-yn-3-ols in the presence of Lewis acid. Oxidation of 8 with Br2 gave pentaleno[1,2-c]pyrroles (10), which is the first reported tricyclic 5/5/5 ring with a fully conjugated system. Structures of these obtained compounds were characterized by spectroscopic methods, and compounds 8a,b and 10c were further confirmed by X-ray crystallographic determination.

Automated summary

This study describes a novel method for preparing tetrahydropentaleno[1,2-c]pyrroles (8) through the reaction of anilines with 1-en-4-yn-3-ols in the presence of Lewis acid. The oxidation of 8 using Br2 resulted in the formation of pentaleno[1,2-c]pyrroles (10), representing the first tricyclic 5/5/5 ring with a fully conjugated system. The structures of the obtained compounds were characterized using spectroscopic methods, with compounds 8a,b and 10c further confirmed by X-ray crystallography.