Synthesis and determination of pKa values of new enantiopure pyridino- and piperidino-18-crown-6 ethers

Abstract

This paper reports the preparation of eight new enantiopure amide type crown ethers and their optically active precursors. Chiral diamines were transformed to amide type pyridino-crown ethers reacting them with pyridine dicarbonyl dichlorides by high dilution technique. Two of the new pyridino-crown ethers were reduced to their piperidino analogues. A preliminary study for the potential application of nanofiltration in the purification and recovery of crown ethers is presented. According to the pKa measurements these eight new macrocycles are potential organocatalysts (for instance in Michael addition reactions) thanks to their acidic and basic moieties and chiral skeletons, respectively.