Abstract Flavanones have been prepared by the cyclization of 2'‐hydroxychalcones using acidic reagents, such as H 2 SO 4 , HX, CF 3 COOH, CH H, KF‐celite, or SiO . Treatment with bases, LiOH, KOH, NaOAc, K CO pyridine, Et N, N ‐methylimidazole afforded flavanones. The conversion to flavanones has conducted Co(salpr), Fe(CN) 6 CuO, Ni(Tfacac) Thioflavanones deprotecting and cyclizing S ‐protecte...