Step-Growth Cyclo-Oligomerization for the Preparation of Di- and Tetrafunctionalized Pillar[5]arenes.

The preparation of complex functionalized pillar[ n]arenes (PA[ n]s) is challenging by one-pot cocyclization or selective deprotection method. We developed a step-growth cyclo-oligomerization method to synthesize functionalized PA[5]s. Dimers, trimers, and tetramers were synthesized and characterized. With this new method, we were able to prepare three di- and tetrafunctionalized PA[5]s. By using a multistep synthetic strategy, the chance to form constitutional isomers and other by-products was reduced. Therefore, complex tetrafunctionalized PA[5]s were prepared with improved yield.