Synthesis and Derivatization of Expanded [n]Radialenes (n=3, 4)

Abstract

Versatile, iterative synthetic protocols to form expanded [n]radialenes have been developed (n=3 and 4), which allow for a variety of groups to be placed around the periphery of the macrocyclic framework. The successful use of the Sonogashira cross-coupling reaction to complete the final ring closure demonstrates the ability of this reaction to tolerate significant ring strain while producing moderate to excellent product yields. The resulting radialenes show good stability under normal laboratory conditions in spite of their strained, cyclic structures. The physical and electronic characteristics of the macrocycles have been documented by UV-visible spectroscopy, electrochemical methods, and X-ray crystallography (four derivatives), and these studies provide insight into the properties of these compounds as a function of pendent substitution in terms of conjugation and donor/acceptor functionalization.

Donor- and/or Acceptor-Substituted Expanded Radialenes: Theory, Synthesis, and Properties

“…28,29 This cross-coupling reaction gave the orthogonally protected expanded [4]radialene 5 in 30% yield, and while this macrocyclization reaction was less efficient than hoped, it gave sufficient material for subsequent derivatization.…”

“…9,10,43−46 To date, however, only a few examples of donor-or acceptor-expanded radialenes have been reported. 18,28 Finally, donor−acceptor-expanded radialenes remain unknown, and there have been no attempts to document cross-conjugated interactions in these derivatives using theory.…”

“…9,10,43−46 To date, however, only a few examples of donor-or acceptor-expanded radialenes have been reported. 18,28 Finally, donor−acceptor-expanded radialenes remain unknown, and there have been no attempts to document cross-conjugated interactions in these derivatives using theory.Our group has recently reported a modular approach for the synthesis of perphenylated expanded [n]radialenes 29 and radiaannulenes. 22,29 This approach has been especially useful in …”

π‐Conjugated Macrocycles Bearing Angle‐Strained Alkynes

“…The strained planar structure of 233 b was determined by using X‐ray crystallographic analysis (CCDC: 652685) . The introduction of a larger substituent on an exo ‐methylene moiety caused the puckering of π‐expanded [4]radialene 235 (38.5°) like cyclobutane rings, which was observed by X‐ray crystallographic analysis (CCDC: 952887; Figure c) . Although a PM3 calculation suggests that the bond angle at the sp carbon of 233 a is smaller than 160°, 233 a was isolated in 32 % yield through the Sonogashira–Hagihara coupling.…”

“…Although a PM3 calculation suggests that the bond angle at the sp carbon of 233 a is smaller than 160°, 233 a was isolated in 32 % yield through the Sonogashira–Hagihara coupling. By introducing phenylethynyl groups, the crystal structure of π‐expanded [3]radialene derivative 234 could be analyzed (CCDC: 942887; Figure b) . This synthetic method could be applied to the preparation of cyclopentamer (45 % yield), but is not applicable to cyclohexamer (<5 %) owing to the competitive polymerization.…”