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A series of 5‐aminothiazolium chlorides (1) bearing tethered benzene ring on N‐3, C‐4 or the exocyclic nitrogen atom are prepared by a three‐component methodology and subjected to basic treatment. The initially generated mesoionic thiazoles 2 undergo internal 1,3‐dipolar cycloaddition across the pendant olefin when the 2‐allylphenyl group is connected to the endocyclic N‐3. The reaction leads to the formation of original N‐bridged thiazoloquinolines as a mixture of two regioisomers 3,4 which are readily separated by chromatography. The structural assignments of the cycloadducts are deduced from their spectroscopic NMR properties and unequivocally established by an X‐ray diffraction analysis. Intramolecular sequence also occurs using the 2‐(allyloxy)phenyl substituent on the same position to give a single regioisomeric 1,4‐methanothiazolobenzoxazepine (7). On the contrary, hydrolysis and ring‐opening or oxidation and rearrangement of the mesoionic intermediates are the exclusive base‐promoted conversions of other thiazolium salts 1.

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A series of 5-aminothiazolium chlorides (1) bearing tethered cycloadducts are deduced from their spectroscopic NMR properties and unequivocally established by an X-ray benzene ring on N-3, C-4 or the exocyclic nitrogen atom are prepared by a three-component methodology and subjected diffraction analysis. Intramolecular sequence also occurs using the 2-(allyloxy)phenyl substituent on the same position to basic treatment. The initially generated mesoionic thiazoles 2 undergo internal 1,3-dipolar cycloaddition across to give a single regioisomeric 1,4-methanothiazolobenzoxazepine (7). On the contrary, hydrolysis and ring-opening the pendant olefin when the 2-allylphenyl group is connected to the endocyclic N-3. The reaction leads to the or oxidation and rearrangement of the mesoionic intermediates are the exclusive base-promoted conversions of formation of original N-bridged thiazoloquinolines as a mixture of two regioisomers 3 ,4 which are readily separated other thiazolium salts 1. by chromatography. The structural assignments of the The synthesis and chemical behaviour of mesoionic ring one of the most powerful methods for the generation of complex systems [2] [9] . Such reactions have been studied with systems have received much attention in the last twenty years [1] [2] . In 1993, we reported the efficient preparation of a range of mesoionic species i. e. dithiolones [10] , sydnones [11] , münchnones [12] [13] , isomünchnones [14] and numerous 5-aminothiazolium salts [3] in the course of a study on the three-component cyclocondensations using thioisomünchnones [15] . Internal cycloaddition of suitable münchnones [13] and isomünchnones [16] provided flexible isocyanides as cyclization reagents [4] [5] . In particular, we showed that the treatment of an aryl chlorodithio or chloro-synthetic approaches to several natural products. Another interesting example is the intramolecular cycloaddition of thionoformate with a mixture of N-benzylidenealkylamine and tert-butyl isocyanide smoothly afforded the 5-(tert-bu-a Reissert salt or open-chain analogue (5-aminooxazolium tetrafluoroborate) on a monosubstituted alkyne to produce tylamino)-4-phenylthiazolium chlorides 1 (R 2 ϭ PhS or pTolO, R 3 ϭ alkyl) which are potential precursors in basic a fused pyrrole by HNCO evolution from the primary dipolar adduct [17] . To date, however, the use of mesoionic media for cyclic azomethine ylides. Reactivities of the corresponding mesoionic thiazoles 2 were examined by the in thiazoles as cyclic azomethine ylides in similar internal reactions was unprecedented. We described here the prepsitu technique [6] with standard electrophilic alkynes and alkenes [7] and carbon disulfide [8] . The reactions involved an aration of eight 5-aminothiazolium chlorides 1 which possess tethered alkenyl moieties and our attempts for their 1,3-dipolar cycloaddition of the "masked" ylides across the carbonϪcarbon or carbonϪsulfur multiple bond, yielding application in heterocyclic chemistry. unstable N-bridged adducts as the first step, and resu...