Mild and Efficient Synthesis of Functionalized Carbazoles via a DBU‐Assisted Sequence Involving Cu‐ and Pd‐Catalyzed Coupling Reactions

Abstract Practical access to diversely functionalized carbazoles has been developed by consecutive Cu‐catalyzed Chan‐Lam N −arylation of various o ‐iodoanilines and boronic acids, and Pd‐catalyzed intramolecular aryl C−H activation of 2‐iodo‐ N ‐arylanilines. Use of 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) as base was found beneficial for both steps. In the Pd‐catalyzed C−H activation step, DBU acts as ligand as well as base, resulting in improved functional tolerance and higher yields than those observed with inorganic or other nitrogen bases. This DBU‐assisted sequence offers access to a variety of carbazoles with various electron‐donating and electron‐withdrawing substituents, including halogens or other reactive functional groups. Twenty‐seven cabazoles with various substitution paterns, including two naturally‐occurring carbazoles ‐ clausine L and clausine H ‐ have been successfully synthesized using these DBU‐promoted metal‐catalyzed coupling reactions.