Reactions of 4,5-dichloroisothiazol-3-ylcarbonitrile with methylmagnesium iodide and ethylmagnesium bromide afforded the corresponding alkyl (4,5-dichloroisothiazol-3-yl) ketones. The reaction of (4,5-dichloroisothiazol-3-yl) methyl ketone with morpholine and piperidine provided 5-morpholino-(piperidino)-substituted derivatives, by the action of sodium borohydride in 2-propanol the keto group was reduced to alcoholic hydroxy group. The bromination of (4,5-dichloroisothiazol-3-yl) methyl ketone with elemental bromine gave bromomethyl (4,5-dichloroisothiazol-3-yl) ketone, whose reaction with thiourea resulted in 2-amino-4-(4,5-dichloroisothiazol-3-yl)thiazole.