One-pot synthesis, quantum chemical calculations and X-ray diffraction studies of thiazolyl-coumarin hybrid compounds.

ABSTRACT

Two closely related hybrid species containing both, thiazolyl and coumarin groups, were synthesized by using two different one-pot procedures from a common precursor. The reaction of α-bromoacetylcoumarin with thioacetamide in methanol furnished 3­(2­methylthiazol­4­yl)­2H­chromen­2­one (2), whereas refluxing α­bromoacetylcoumarin with potassium thiocyanate in ethanol afforded 3­(2­ethoxythiazol­4­yl)­2H­chromen­2­one (3). Both derivatives were fully characterized by spectroscopic methods, elemental analysis and X-ray diffraction studies. Intramolecular C4H⋯N and C5'H⋯OC hydrogen bonds between the heterocycles determine the conformational behavior. The co-planarity of the coumarin and thiazolyl rings favors the occurrence of two remote orbital interactions involving the oxygen and nitrogen lone pairs and the corresponding σ*CH electron acceptor, as demonstrated by Natural Bond Orbital population analysis. The 2-substitution of the thiazol­4­yl group has little effect on the molecular structures but causes significant differences in the crystal packing of the two compounds.