Iminium Salts in Solid-State Syntheses Giving 100% Yield

Abstract

Numerous reaction types in the field of iminium salts are performed in the gas-solid and solid-solid techniques in order to reach 100% yield. The stoichiometric runs are waste-free and do not require costly workup. Frequently, iminium salts were avoided, as acid catalysis was dispensable. Thioureas and α-halogenated ketones give a variety of 2-aminothiazoles via thiuronium salts in quantitative yield. A new intramolecular solid-state thermal condensation is reported. Enaminoketones are synthesized quantitatively from anilines and 1,3-diketones without catalysis and those can be used for quantitative solid-state 4-cascade reactions. Solid paraformaldehyde is used to produce methylene imines and internally trapped methylene iminium salts. Benzoylhydrazones are produced again without catalysis in the solid state. Vacuum and ball-mill techniques are particularly useful in the production of highly sensitive iminium salts. Hexahydro-1,3,5-triazines cyclorevert upon exposure to HCl gas to give solid arylmethylene iminium chlorides as new versatile reagents. These are used in arylaminomethylations of β-naphthol and of themselves to give Troeger's bases in 3-cascades. More direct are 4-cascade Troeger's base syntheses by dissolving hexahydro-1,3,5-triaryltriazines in trifluoroacetic acid. Alkylations of imines with trimethyloxonium tetrafluoroborate and triphenylmethyl cation give highly sensitive quaternary iminium salts in the ball-mill. The products are characterized by spectroscopic techniques and density functional theory (DFT) calculations at the B3LYP 6-31G* level. Molecular movements in the crystal and surface passivation are investigated with atomic force microscopy (AFM) techniques.