Synthesis of the thiazolo[3,2-a]quinolinium system

Abstract

Keywords: 1-bromomethylthiazolo[3,2-a]quinolinium bromide, propargyl bromide, 1-iodomethylthiazolo[3,2-a]quinolinium iodide, 2-mercaptoquinoline, 2-propargylthioquinoline.The synthesis of the thiazolo[3,2-a]quinolinium system is carried out by dehydration of -(2-quinolylthio) ketones [1] or -(quinolylthio)acetic acids [2], and the halocyclization of 2-vinylthioquinoline [3].We have shown that the reaction of 2-propargylthioquinoline (1) with bromine or iodine does not stop at the stage of formation of 1-halomethylidene-1,2-dihydrothiazolo[3,2-a]quinolinium halides 2a,b but further isomerizes to give the 1-halomethylthiazolo[3,2-a]quinolinium halides 3a,b. Compound 1 was prepared by the reaction of 2-mercaptoquinoline with propargyl bromide in the presence of sodium 2-propoxide in 2-propanol. N SH Br N S N H S N S X X X 2 N S X X 1 2n+1 3a,b 2n+1 2a,b 2-PrONa, 2-PrOH + + 2, 3 a X = I, n = 0; b X = Br, n = 1The 1 H NMR spectra for compounds 3a,b show signals for the protons of the CH 2 I (4.71) or CH 2 Br group (4.74 ppm) and for the H-2 proton at 8.09 and 8.04 ppm respectively.In contrast to compound 1 the 3-formyl-2-propargylthioquinoline reacts with the halogens to form 1-halomethylidene-2H-thiazolo[3,2-a]quinolinium halides [4].1 H NMR spectra were recorded on a Bruker DRX-400 spectrometer (400 MHz) using DMSO-d 6 and with TMS as internal standard. Mass spectra (EI, 70 eV) were taken on a Hewlett-Packard GC/MS instrument with an HP-5890 gas chromatograph.