The reaction is named after two chemists who devoted part of their careers to research into this synthetic method, the German chemist Kurt Lehmstedt and the Romanian chemist Ion Tănăsescu. Variations of the reaction name include Lehmsted–Tănăsescu reaction, Lehmsted–Tănăsescu acridone synthesis and Lehmsted–Tanasescu acridone synthesis.
Reaction mechanism
In the first step of the reaction mechanism the precursor molecule 2-nitrobenzaldehyde 4 is protonated, often by sulfuric acid, to intermediate 5, followed by an electrophilic attack to benzene (other arenes can be used as well). The resulting benzhydrol6 cyclisizes to 7 and finally to compound 8. Treatment of this intermediate with nitrous acid (sodium nitrite en sulfuric acid) leads to the N-nitroso acridone 11 via intermediates 9 en 10. The N-nitroso group is removed by an acid in the final step. The procedure is an example of a one-pot synthesis.
References
^S Yoshida. Design, Synthesis and Characterization of Novel Heterocyclic Polymers (Thesis, McGill University, Montreal (Canada))