An Expedient Flow Chemistry Approach to Substituted 1,4-Dimethylcarbazoles

Abstract

A simple, expedient continuously scalable flow chemistry synthesis of a range of 1,4-dimethylcarbazoles from substituted indoles and 2,5-hexanedione in the presence of K-10 (montmorillonite clay) is reported. Optimization of the flow conditions led to the development of an in-house K-10/sand Omnifit^TM catalyst column that at 140 °C and 0.4 mL.min⁻¹ afforded >90% conversion of the selected indole to the desired 1,4-carbazole. This equates to a ca 80 mg.h⁻¹ production rate. The reaction was tolerant of electron donating indoles but not electron withdrawing indoles.