Synthesis, Mechanism and Catalytic Applications of Pillar[n]arenes

Pillar[n]arenes (P[n] n = 5-15) are a new class of macrocyclic arenes discovered for the first time by Ogoshi in 2008, which attracted a lot of attention due to their unique binding properties towards neutral electron poor compounds. Our research was focused on the enhancement of the yield of the larger macrocycle P[6], starting from three different alkoxy substituted benzene derivatives. Our synthetic approach involved the study of a series of small organic and organometallic cations in the role of a template, such as a cobaltocenium salt, ferrocenium salt, tetramethylammonium chloride and butyl methyl imidazolium salt. Through mass spectroscopy we further investigated the reaction templated by the quaternary ammonium salt and promoted by the presence of FeCl3. We finally tuned the experimental conditions for the conversion of both P[5] and its oligomeric by-products into P[6]. Finally our group studied the catalytic effect of the presence of P[5] in nucleophilic substitution reactions, observing a rate acceleration between 10 and 20 times when the substrates were allyl halides and primary linear amines. This was the first example of the use of pillararenes as real organocatalysts.