The total synthesis of (+/-)-TAN1251A possessing an antimuscarinic activity was achieved. Carboxylic acid (1) was converted into carbamate (3) through a sequence of alkylation and Curtius rearrangement. After a few functional group interconversions of 3, the corresponding amine (9) was converted into an azaspiro molecule (18) through cyclization and installation of a C 2 unit. Hydrolysis of 18 followed by lactam formation afforded tricyclic compound (20). Coupling of 20 with aldehyde (22) gave two epimeric adducts, (23A) and (23B), which were converted into TAN1251A by four steps.