Didymeline is an alkaloid with an azaspiro tricyclic skeleton with various functionalities. Despite the fact that its unique architecture is synthetically attractive, its total synthesis has never been achieved before. Herein, we present synthetic studies on the core structure of didymeline. Accordingly, a spiro ring system was constructed through dearomatization of a phenol derivative with α-diazoamide unit. Based on the resulting 2-azaspiro[4,5]decane variant, a tricyclic molecule was synthesized via base-promoted intramolecular ring closure. For an asymmetric synthesis, an enantioselective dearomatization was also examined under silver catalysis, which led to the formation of an all-carbon substituted quaternary stereogenic center. © 2021 Japan Institute of Heterocyclic Chemistry. All rights reserved.