A new preparation of substituted 4<i>H</i>‐1‐benzothiopyran‐4‐ones from c(α)<i>N</i>‐benzoylhydrazones or c(α)<i>N</i>‐carboalkoxyhydrazones and methyl thiosalicylate

Abstract

Abstract C(α) N ‐Benzoylhydrazones or C(α), N ‐carboalkoxyhydrazones were dilithiated with excess lithium diisopropylamide, and the dianion‐type intermediates were condensed with lithiated methyl thiosalicylate, followed by cyclization/hydrolysis to substituted 4 H ‐1‐benzothiopyran‐4‐ones (thioflavones/thiochromones).