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 pyrido1,2‐αindoles, 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.