Transition-Metal-Free Synthesis of Imidazo[2,1-b]thiazoles and Thiazolo[3,2-a]benzimidazoles via an S-Propargylation/5-exo-dig Cyclization/Isomerization Sequence Using Propargyl Tosylates as Substrates

Publikations-Art

Zeitschriftenbeitrag (peer-reviewed)

Autoren

Omar, M. A.; Frey, W.; Conrad, J.; Beifuss, U.

Erscheinungsjahr

2014

Veröffentlicht in

J. Org. Chem

Band/Volume

79/

DOI

10.1021/jo501980w

Seite (von - bis)

10367-10377

A transition-metal-free route for the synthesis of several N-fused heterocycles, including thiazolo[3,2-a]benzimidazoles and imidazo[2,1-b]thiazoles, is reported. The reaction between propargyl tosylates and 2-mercaptobenzimidazoles under basic conditions results in 3-substituted thiazolo[3,2-a]benzimidazoles, in yields up to 92% in a single synthesis step. With 2-mercaptoimidazoles as the substrate, the corresponding imidazo[2,1-b]thiazoles were exclusively obtained. The transformation is considered to proceed as an intermolecular S-propargylation that is followed by 5-exo-dig ring closure and double-bond isomerization.