A review of the syntheses of flavanones, thioflavanones, and azaflavanones from 2'‐substituted chalcones
Jae In Lee
Abstract
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 3 SO 3 H, KF‐celite, or SiO 2 . Treatment of 2'‐hydroxychalcones with bases, such as LiOH, KOH, NaOAc, K 2 CO 3 , pyridine, Et 3 N, or N ‐methylimidazole afforded flavanones. The conversion of 2'‐hydroxychalcones to flavanones has been conducted using Co(salpr), K 3 Fe(CN) 6 , CuO, or Ni(Tfacac) 2 . Thioflavanones have been prepared by deprotecting and cyclizing S ‐protected chalcones using AgNO 3 , HBr, CF 3 COOH, or NaOH and by adding NaSH or KCS 2 OEt to 2'‐halochalcones and subsequent substitution. Azaflavanones have been prepared by cyclizing 2'‐aminochalcones using acidic reagents, such as H 3 PO 4 , HCl, silica chloride, or K‐10 clay. Furthermore, treatment of 2'‐aminochalcones with Lewis acids, such as ZnCl 2 , SbCl 3 , Yb(OTf) 3 , InCl 3 , TaBr 5 , or CeCl 3 afforded azaflavanones, and chiral azaflavanones were prepared by cyclizing 2'‐aminochalcones in the presence of per‐6‐ABCD, chiral amine, BINOL‐phosphoric acid, or thiourea catalyst.