Modular Synthesis of Bicyclic and Tricyclic (Aza‐) Arenes from Nucleophilic (Aza‐)Arenes with Electrophilic Side Arms via [4+2] Annulation Reactions

An efficient strategy for the synthesis of bicyclic and tricyclic (aza‐)arenes from a nucleophilic (aza‐)arene with an electrophilic side arm was developed. The (aza‐)arene precursor has both nucleophilic and electrophilic sites, which were fixed at a 1,4‐distance. The bicyclic and tricyclic (aza‐)arene products were constructed via [4+2] annulation by using scandium(III) triflate as a catalyst and enolizable ketones or aldehydes as the counterpart reagents. A variety of six‐membered carbocycles and heterocycles, such as indolizines, indoles, naphthalenes, carbazoles, and pyrido[1,2‐α]indoles, were successfully synthesized. Some one‐pot sequential reactions were also developed, in which the 1,4‐donor‐acceptor precursors can be synthesized via oxidation of alcohols or a proper condensation reaction.