Step-Growth Cyclo-Oligomerization for the Preparation of Functionalized Pillar[6]arenes with Alternating Methylene Bridge Substitutions

Abstract

Methylene-bridge-substituted pillar­[6]­arenes (PA[6]) are synthesized by step-growth cyclo-oligomerization. Dimers, trimers, tetramers, and hexamers with substituted methylene bridges are synthesized. Hexamers are converted to PA[6] derivatives with alternating methylene bridge substitutions by ring-closing reactions. PA[6] derivatives are further modified with pyrene groups or carboxylate groups by Suzuki–Miyaura coupling reactions. The modifications render PA[6] fluorescent or water-soluble. A host–guest chemistry study confirms that the water-soluble PA[6] derivative is a high-affinity host toward suitable guests in water.

Pillar[5]arene-based Neutral Radicals with Doublet Red Emissions and Stable Chiroptical Properties

“…Macrocyclic pillararenes have been widely explored for the chemistry in host–guest recognition and supramolecular self-assembly owing to their unique structures and accessible synthetic approaches. − Meanwhile, pillararenes are also planar chiral motifs as a result of the orientational alkoxy groups attached to macrocyclic rings (Scheme ). Although two of the stereoisomers ( p S and p R) can usually racemize under ambient conditions, many efforts have been made to sterically stabilize enantiomers by several research groups. , Although parent pillararenes with nonconjugated skeletons exhibit negligible emissions, π-conjugated luminophores and highly emissive functionalities can be employed to efficiently address these issues, and thus their CPL properties have been reported very recently by our group and others .…”

Friedel–Crafts Acylation for Accessing Multi‐Bridge‐Functionalized Large Pillar[n]arenes

“…The two hydroxymethylene groups can orient to opposite or the same directions to yield trans‐ or cis‐ isomers, respectively. Previous research of pillar[ n ]arenes with multi‐functionalized bridges all resulted in inseparable steric isomers, leading to unclear structures [19,20a] . In this work, the two generated isomers can be separated by chiral column (Figure S1) and characterized in detail.…”

Stereoselective Single Step Cyclization to Give Belt-Functionalized Pillar[6]arenes

“…Subsequent coupling of these dimers using paraformaldehyde gave the 1,3,5-trifunctionalized P6 deriva- tives Ar 3 −P6 Me nonstereoselectively, and these could then be further functionalized at the aryl groups (Figure 1). 39 While belt-functionalized pillar[n]arenes have shown interesting properties, they have received relatively little attention. Perhaps most surprisingly, we are unaware of any reports of the synthesis of belt-functionalized pillar[n]arenes by a direct cyclization approach, i.e., by the reaction of a 1,4-dialkoxybenzene with an aldehyde other than paraformaldehyde or by the direct reaction of an appropriate monomer, such as a 1,4dialkoxybenene, featuring a secondary benzylic alcohol.…”