Synthetic Approaches to 2‐Alkylthiochroman‐4‐ones and Thioflavanones

Abstract

2‐Alkylthiochroman‐4‐ones have been synthesized by acid‐catalyzed cyclodehydration of 3‐alkyl‐3‐(phenylthio)propanoic acids, Friedel–Crafts acylation of 3‐alkyl‐3‐(phenylthio)propanoyl chlorides with Lewis acids, direct reaction of thiophenols and acrylic acids using CF3SO3H, and 1,4‐addition of organometallic reagents to thiochromones. Furthermore, thioflavanones have been synthesized by cyclization of 3‐phenyl‐3‐(phenylthio)propanoyl chlorides with Lewis acids, incorporation of sulfur atoms into 2'‐halochalcones and subsequent cycloelimination, 1,4‐addition of S‐protected chalcones, direct condensation of 2'‐mercaptoacetophenone with arylaldehydes using lithium diisopropylamide, conjugate addition of organometallic reagents to thiochromones, and hydrogenation of thioflavones.

Progress on the Cu-Catalyzed 1,4-Conjugate Addition to Thiochromones

“…Although the conjugate addition of stoichiometric amount of organocuprates to thiochromones were also reported [ 9 , 10 ], this review will focus on recent progress on the conjugate additions of organocopper reagents to thiochromones especially those using catalytic amount of copper (I) salts in the synthesis of an important class of sulfur-heterocycles-2-alkylthiochroman-4-ones and thioflavanones. Other synthetic approaches to 2-alkylthichroman-4-ones and thioflavanones were well summarized in a recent review article [ 11 ] and this review aims to provide more details on the progress on synthesis of 2-substituted thichroman-4-ones via conjugate addition of Grignard reagents catalyzed by copper salts. This review also aims to give an introduction to the history, development of the organocuprates and especially their applications in the synthesis 2-substituted thiochroman-4-ones.…”