3a,4,5,6-Tetrahydro-1H,3H-naphtho[1,8-cd]pyran-1-one is an intermediate in the synthesis of (S,S)-Palonosetron Acid which is an impurity in the synthesis of (S,S) Palonosetron (P165800), serotonin 5-HT3 receptor antagonist used in the prevention and treatment of chemotherapy-induced nausea and vomiting (CINV). Antiemetic.