DMAP-promoted cascade C–S/C–N bonds formation approach to 1,3-thiazolidin-4-ones via annulation of β-ketothioamides with α-halocarboxylic acids at room temperature

Chemistry of Ketene N,S-Acetals: An Overview

“…In the case of biselectrophiles being utilized, cyclic ketene N , S -acetals can be constructed. Catalyzed by 4-dimethylaminopyridine (DMAP), [3 + 2] annulation of 67 with diethyl but-2-ynedioate as the 1,2-dielectrophile via a sequential thia-Michael addition/intramolecular amidation afforded cyclic ketene N , S -acetals − having the structural features of enamides − in high yields (Scheme , 16 examples, 75–92% yields). The merit of this reaction is highlighted by its operational simplicity, short reaction time (3–10 min), very mild reaction conditions, and tolerance of a large variety of functional groups for β-ketothioamides .…”

“…The merit of this reaction is highlighted by its operational simplicity, short reaction time (3–10 min), very mild reaction conditions, and tolerance of a large variety of functional groups for β-ketothioamides . Similarly, 68p – r were obtained by use of α-halocarboxylic acid anhydrides [in situ generated from α-halocarboxylic acids in the presence of dicyclohexylcarbodiimide (DCC) at room temperature] as the 1,2-dielectrophiles . For the formation of 68p – r , a plausible mechanism involving intermolecular S N 2 displacement was proposed by the authors, although an intramolecular S N 2 displacement (for ring closure) seems more appropriate, especially for the formation of 68p , on account of the great steric hindrance of an intermolecular S N 2 at a tertiary center. , Alternatively, another possibility for formation of 68p – r may occur via a sequence of acylation of the amino nitrogen of 67 by 2-chloro-2-methylpropanoic acid anhydride, where the amide N atom participates in intramolecular displacement of the Cl atom to give an aziridinonium cation that is then displaced by the sulfur atom.…”

β-Ketothioamides: efficient reagents in the synthesis of heterocycles

“…As shown in Scheme 6, Singh and coworkers reported a one-pot synthesis of 1,3-thiazolidin-4-ones starting from β-ketothioamides with in situ generated acid anhydride from α-halocarboxylic acid in the presence of DCC at room temperature. 12 The features of this method involve forming C-S and C-N bonds and one ring in a single synthetic operation, mild reaction conditions and is metal-free. A possible mechanism including the nucleophilic attack by thiocarbonyl sulfur of KTAs followed by intramolecular N-cyclization processes is proposed.…”