The reaction of 2-allyl(propargyl)thioquinolin-3-carbaldehyde with halogens (Br or I) results in formation of 1-halogenomethyl(halogenomethylidene)-4-formyl-1,2-dihydrothiazolo[3,2- a]-quinolinium trihalogenide. In the case of the propargylic derivative the process is stereoselective.