Synthesis and self-aggregation of enantiopure and racemic molecular tweezers based on the bicyclo[3.3.1]nonane framework.

A pair of molecular tweezers (syn-4) that consists of quinoline and pyrazine units fused to a bicyclic framework is presented. The tweezers were synthesised both as a racemic mixture (rac-4) and an enantiomerically pure form ((R,R,R,R)-4) starting from either racemic or enantiomerically pure bicyclo[3.3.1]nonane-2,6-dione (3). Homochiral dimers were observed in the solid state for rac-4. The self-association of both rac-4 and (R,R,R,R)-4 was studied in solution. A weak self-association constant in CDCl(3) was estimated by (1)H NMR spectroscopic dilution titration experiments in both cases, following several proton resonances. For this purpose, a general normalisation model for the accurate determination of association constants from multiple datasets was developed. In contrast to the solid state, no diastereomeric discrimination was observed for rac-4 in solution.