Synthesis of new heterocycles via ring transformation and 1,4-dipolar cycloaddition reactions of thiazolium-betaines

Abstract

Thiazolium-betaines, which are highly reactive organic compounds, can be used for the synthesis of the complicated hetero cyclic compounds via ring transformation and 1,4-dipolar cycloaddion reactions. On the reaction of 7-dithiocarboxy-3-phenyl-5,6-dihydroimidzo [2,1-b]thiazolium-betaine(10c) with para-substituted phenacyl bromides, in case that the substituent R was chloro, bromo, or nitro group, the ring transformation compound(19) was obtained. But when R was methoxy group, the quartemary ammonium salt(20) was formed. The reaction of 10c with unsubstituted phenacyl bromide(R=H) gave 19a and 20a to the similar ratio, respectively. When 10c was reacted with $\alpha$ -chloroacetone or ethyl 4-chloroacetoacetate, the new heterocycle(23) was obtained via ring transformation reaction. On the other hand, in case that 10c was reacted with methyl bromoacetate or ethyl bromoacetate, the quarternary ammonium salt(24) was formed. The reaction of 3-phenyl-9-[N-phenyl (thiocarbamoyl)]5,6,7,8-tetrahydrothiazolo [3,2-a][1,3] diazepinium-betaine(10f) with alkylating agents gave two major products via ring transformation reaction. These products (25a,25b) were considered as the structural isomers of syn-and anti. The 1,4-dipolar cycloaddition reaction of 3-phenyl-7-[N-phenyl-(carbamoyl)]-5,6-dihydroimidazo[2,1-b] thiazolium-betaine(10b) with phenacyl bromide provided the new diastereomeric heterocycles(37a,37b) via 1,4-dipolar cycloaddition in place of ring transformation reaction. Also the reaction mechanism and structure elucidation of cycloadducts(37a,37b) were described. Then, the thermal conversion between 1,4-dipolar cycloadducts, from a kinetically controlled product to a thermodynamically controlled product, was detected by1H nmr spectroscopic study according to temperature and time. And various 1,4-dipolar cycloadduct derivatives (41-46) were synthesized by the reaction of 10b with a series of para-substituted phenacyl bromides. In case that the substituent R was me...