Pyrrolation of Melem: A Facile Gateway into the Field of Monomeric s-Heptazine Chemistry.

Abstract

Monomeric s-heptazines are an intriguing class of compounds with many attractive properties for various areas of application such as photocatalysis or organic light-emitting diodes. However, research into these properties has so far been challenging, as only a few synthetic routes for the preparation of monomeric s-heptazines are known in the literature. Furthermore, these few reported synthetic pathways generally require the use of specialized equipment that may not be available to all laboratories interested in studying monomeric s-heptazines. For this reason, a more accessible synthetic route for the preparation of monomeric s-heptazines has been developed in the course of this work. The central compound of this new approach is 2,5,8-tri(1H-pyrrol-1-yl)-s-heptazine, which could be conveniently synthesized via an acid catalyzed pyrrolation of melem with bench-stable 2,5-dimethoxytetrahydrofuran in a simple one-pot synthesis in air. This compound was shown to be a potent starting material for the synthesis of numerous other monomeric s-heptazines by reaction with both nucleophiles and electrophiles. The monomeric s-heptazines thus accessible were analyzed for their crystal structures by single crystal X-ray diffraction and for their optical properties by ultraviolet/visible and photoluminescence spectroscopy.