The Trouble with Five: New Synthetic Strategies toward C5 -Symmetric Pillar[5]arenes and Beyond

Abstract

Rim-differentiated pillar[5]arenes (P[5]s) are intriguing macrocyclic molecular platforms with C 5-symmetry, but their conventional statistical syntheses suffer from low yields and laborious separation. Our group recently reported a ‘pre-oriented’ protocol that results in highly selective production of C 5-symmetric P[5]s among four constitutional isomers. Subsequently, we devised a more general divergent synthetic route starting with a common P[5] precursor with rim differentiation, followed by a series of high-yielding reactions that permit successive transformations of both rims freely. As a result, a variety of rim-differentiated P[5]s can be made to order in gram-scale quantities. This total solution not only populates the list of C 5-symmetric P[5]s, but also enables further design and synthesis of assorted five-fold organic building blocks towards complex supramolecular architectures.

Stereochemical Inversion of Rim-Differentiated Pillar[5]arene Molecular Swings

“…First, a series of rim-differentiated P[5]­s 1a – 1e were synthesized (Scheme ) using the methodology we recently developed . Per-functionalized P[5]­s 2a – 2c were prepared by following the procedures reported in the literature. , We briefly describe this procedure for one of the compounds under study, a rim-differentiated P[5] with 4-cyanobenzyl moieties on one rim and methyl groups on the other, (4-cyanobenzyl) 5 (Me) 5 -P­[5] 1d (see also the Experimental Section).…”

“…However, progress on DNMR studies of such rim-differentiated P[5]s was hampered by their inefficient syntheses and difficult purification steps. In recent years, our research group has developed 17 efficient methods for the synthesis and derivatization of C 5 -symmetric rim-differentiated P[5]s that largely overcome these limitations.…”

Iteroselectivity, the missing sibling of chemo-, regio- and stereoselectivities

“…In 2014, we proposed to name this selectivity "iteroselectivity" 5 and, since then, this term was used in various articles. 6,7,8,9,10,11,12,13,14 To the best of our knowledge, the concepts arising from this type of selectivity have not been yet properly named and defined in the literature.…”

Discrete Macrocycles with Fixed Chirality and Two Distinct Sides: Dipole‐Dependent Chiroptical Response

“…Different from other π‐conjugated macrocycles, C 5 ‐symmetric rim‐differentiated pillar[5]arenes have been actively investigated with established synthetic methods using pre‐oriented monomers [19, 20, 21a,b] . Such compounds have attracted much attention as two‐sided macrocycles in forms of racemates, while chiroptical properties were not actively examined [19, 21–24] . In the present work, we designed a series of rim‐differentiated pillar[5]arenes bearing bulky cyclohexylmethoxy and aryl groups to fix planar chirality ( 3R in Scheme 1).…”