One-Pot Three-Component Synthesis of N-Arylmethyl-4-(7-cyclohepta-1,3,5-trienyl)anilines

We report a one-pot three-component synthesis of N-arylmethyl-4-(7-cyclohepta-1,3,5-trienyl)anilines by using various aromatic imines, tropylium tetrafluoroborate, and sodium tetrahydroborate in the presence of imidazole as activator.


Introduction
Nitrogen-containing compounds with the 1,3,5-cycloheptatriene fragment have a marked biological action [1,2].The use of tropylium salts (tetrafluoroborate or perchlorate) is a method to introduce the 1,3,5-cycloheptatriene cycle into aniline molecules and into its substituted molecules.Anion in a tropylium salt influences the N- [3] or C- [1] tropylation process of aniline, of arylamines or of N-substituted anilines, and a yield of final products.
Earlier [5], we had reported the reducing reaction of imine hydrotropylation in the "tropylium perchloratesodium tetrahydroborate" system resulting in unstable tertiary amines, namely N-phenyl-N-arylmethyl-N-(7cyclohepta-1,3,5-trienyl)anilines.However, direction of this reaction changes after addition of imidazole to the reaction mass.Imidazole promotes a shift of the tropylium moiety from the nitrogen atom to para-position of the aniline ring and, thus, leads to formation of such stable products as N-arylmethyl-4-(7-cyclohepta-1,3,5trienyl)anilines.The educed products contain two important biogenic moieties, namely tropilidene cycle and NH-group.The NH-group-in accordance with investigations in modeling and in predicting properties of active heterocyclic compounds based on the "structure-actiontoxicity" link [6]-promotes an increase in pharmacological action and a decrease in toxicity of compounds, so important for investigations in growth control of crops.
Thus, the use of tropylium perchlorate enabled educing para-tropylated aniline [1] which had been inaccessible earlier [7], as well as secondary tropylated amines by using the ionic imine-hydrotropylation reaction [5].A disadvantage of these methods is the use of explosive tropylium perchlorate.
A role of the activator is, probably, to form the B complex promoting a shift of the cycloheptatriene cycle to the para-position of the aniline fragment of the A intermediate (Scheme 2).

Experimental Part
The FTIR spectra were registered by using the IR Fourier spectrometer (Bruker, Germany), registration condition: suspension in vaseline oil.The 1 H NMR spectra were registered by using the Mercury 300 device (300 MHz), with hexamethyldisiloxane (HMDSO) as internal standard.Chromatograph mass spectrum was recorded by using the Agilent Technologies 689ON/597B device, the HP-5ms column (30 × 0.25 mm, helium as carrier gas, ionization by 70 eV electron shock, 100˚C temperature of the column's thermostat, 250˚C, 270˚C temperature of evaporator); CHNS-932 (Carbon, Hydrogen, Nitrogen and Sulfur Determinator), LECO Corporation (USA).

General Preparation Procedure for the 3a-e Compounds
Imine (1 mmol) is dissolved in 5 ml of tetrahydrofuran, whereupon tropylium tetrafluoroborate (1 mmol), sodium tetrahydroborate (1 mmol), and imidazole (0.5 mmol) are added at one go.The reaction mass is then stirred for 2.5 h at room temperature, diluted with water, and neutralized to pH 7.
The advantage of this method is the use of safe-tohandle tropylium tetrafluoroborate (instead of tropylium perchlorate), and the increased yield of the 3b-d com-pounds.
The advantage of the use of tropylium tetrafluoroborate is that higher yields for the 3b-d compounds are achieved as compared with tropylium perchlorate [5].
The educed compounds contain two biogenic moieties, namely NH group and tropilidene cycle.