Herein is reported the nine-step commercial synthesis of delgocitinib, a Janus kinase inhibitor approved for the treatment of atopic dermatitis in 2020. Its chiral spirodiamine core was selectively constructed by an intramolecular SN2 reaction of the suitably designed γ-lactone substrate and a few subsequent steps including a selective γ-lactone ring-opening reaction with potassium phthalimide, hydrazine-free mild dephthaloylation, and one-pot reduction of β- and γ-lactams. The route affords chemically and stereochemically pure delgocitinib in 39% yield.