Synthesis of α-Halo-γ-hydroxyenamides by Titanium Tetrahalide Mediated Addition of Aldehydes or Ketones to Ynamides

Abstract

α-Chloro- or α-bromo-γ-hydroxyenamides were synthesized by the reaction of an ynamide, titanium tetrahalide, and an aldehyde or a ketone. A γ-hydroxy trisubstituted enamide was prepared stereoselectively by Suzuki coupling of an obtained α-chloro-γ-hydroxyenamide with phenyl boronic acid. Intramolecular cyclization of α-chloro-γ-hydroxyenamide took place to provide a 2,3-dihydrobenzoisothiazole 1,1-dioxide derivative by palladium-catalyzed C-H activation of the tosyl group. Hydrochlorination of ynamides proceeded to give α-chloroenamides by treatment with titanium tetrachloride followed by addition of water.