The Synthesis and Characterization of all Diastereomers of a Linear Symmetrically Fused Tris‐Tröger's Base Analogue: New Chiral Cleft Compounds

The synthesis and characterization of all diastereomers of a linear symmetrically fused tris‐Tröger's base analogue are described. The diastereomers are unambiguously assigned as syn – anti 1 a , anti – anti 1 b , and syn – syn 1 c 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‐Tröger's base analogue have been synthesized. Molecules 1 a and 1 c are new cleft compounds and analysis of compound 1 a in the solid state shows inclusion of one molecule of CH 2 Cl 2 in the larger aromatic cleft, whereas in isomer 1 c disordered solvent molecules are trapped in the extended aromatic cleft. Furthermore, in the solid state, isomer 1 c 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 1 a – 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 °C. This observed configurational stability at the stereogenic nitrogens of 1 a – c is unique for analogues of Tröger's base in general to date. Finally, the ratio of cleft compounds 1 a and 1 c significantly increased relative to cavity compound 1 b when ammonium chloride was used as an additive in the Tröger's base condensation to 1 a – c suggesting a templating effect of the ammonium ion.