Evelyne Marchand

5-Aminothiazolium Salts as Potential Cyclic Azomethine Ylides – Base-Induced Intramolecular Cycloaddition Reactions ofN-(o-Allylphenyl)- andN-(o-(Allyloxy)phenyl)-Substituted Derivatives

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.

Addition of isocyanides to ?-(methylthio)-benzylidenamidinium iodides: A surprising access to 2-(dialkylamino)imidazoles and 3,5-diamino-2H-pyrrolium salts

A number of 2-(dialkylamino)-5-(methylthio)imidazoles 2 are obtained by treating the formamidinium iodides 1a,b with isocyanides R3 NC under mild conditions. Reduction of these species can occur in the reaction medium to furnish the corresponding imidazoles 3. In some cases, double cycloaddition across the imine bond of starting salts 1 also provides the (azetidin-1-yl-methylene)ammonium iodides 4. Reactions with tert-butyl and isopropyl isocyanides in refluxing acetonitrile convert the acetamidinium iodide 1c into the 3,5-diamino-2H-pyrrolium salts 7. Mechanisms are suggested to account for these ring-closure processes.