title: 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.
abstract: 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.
authors.affiliation: Bioorganische Chemie, Institut für Chemie, Universität Hohenheim , Garbenstraße 30, D-70599 Stuttgart, Germany.
authors.forename: Mohamed A
authors.initials: MA
authors.lastname: Omar
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Frey
authors.forename: Jürgen
authors.initials: J
authors.lastname: Conrad
authors.forename: Uwe
authors.initials: U
authors.lastname: Beifuss
mesh_terms: D001557:Benzenesulfonates / Q000737:chemistry*; D001562:Benzimidazoles / Q000737:chemistry*; D003500:Cyclization; D007536:Isomerism; D010293:Pargyline / Q000031:analogs & derivatives / Q000737:chemistry*; D013844:Thiazoles / Q000737:chemistry*; D028561:Transition Elements / Q000737:chemistry*
chemical_list: C573194:4-methylbenzenesulfonic acid; D001557:Benzenesulfonates; D001562:Benzimidazoles; D013844:Thiazoles; D028561:Transition Elements; D010293:Pargyline