The synthesis and characterization of all diastereomers of a linear symmetrically fused tris-Troger's base analogue:: New chiral cleft compounds

The synthesis and characterization of all diastereomers of a linear symmetrically fused tris-Troger's base analogue are described. The diastereomers are unambiguously assigned as syn-anti 1a, anti-anti 1b, and syn-syn 1c isomers, by using X-ray diffraction analysis and NMR spectroscopy. For the first time, the anti-anti and the syn-syn diastereomers of a linear symmetrically fused tris-Troger's base analogue have been synthesized. Molecules 1a and 1c are new cleft compounds and analysis of compound 1a in the solid state shows inclusion of one molecule of CH2Cl2 in the larger aromatic cleft, whereas in isomer 1c disordered solvent molecules are trapped in the extended aromatic cleft. Furthermore, in the solid state, isomer 1c forms infinite open channels along one of the crystallographic axes and perpendicular to this axis there are infinitely extending "wedged-ravines". Importantly, each of the diastereomers 1a-c is resistant to inversion at the stereogenic nitrogen atoms under strongly and weakly acidic conditions in the range from room temperature (RT) to 95 degrees C. This observed configurational stability at the stereogenic nitrogens of 1a-c is unique for analogues of Troger's base in general to date. Finally, the ratio of cleft compounds 1a and 1c significantly increased relative to cavity compound 1b when ammonium chloride was used as an additive in the Troger's base condensation to 1a-c suggesting a templating effect of the ammonium ion.