A review of the syntheses of flavanones, thioflavanones, and azaflavanones from 2'‐substituted chalcones

Abstract

AbstractFlavanones have been prepared by the cyclization of 2'‐hydroxychalcones using acidic reagents, such as H2SO4, HX, CF3COOH, CH3SO3H, KF‐celite, or SiO2. Treatment of 2'‐hydroxychalcones with bases, such as LiOH, KOH, NaOAc, K2CO3, pyridine, Et3N, or N‐methylimidazole afforded flavanones. The conversion of 2'‐hydroxychalcones to flavanones has been conducted using Co(salpr), K3Fe(CN)6, CuO, or Ni(Tfacac)2. Thioflavanones have been prepared by deprotecting and cyclizing S‐protected chalcones using AgNO3, HBr, CF3COOH, or NaOH and by adding NaSH or KCS2OEt to 2'‐halochalcones and subsequent substitution. Azaflavanones have been prepared by cyclizing 2'‐aminochalcones using acidic reagents, such as H3PO4, HCl, silica chloride, or K‐10 clay. Furthermore, treatment of 2'‐aminochalcones with Lewis acids, such as ZnCl2, SbCl3, Yb(OTf)3, InCl3, TaBr5, or CeCl3 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.