Abstract
[2.2]Paracyclophane (PCP) is a prevalent scaffold that is widely utilized in asymmetric synthesis, π‐stacked polymers, energy materials, and functional parylene coatings that finds broad applications in bio‐ and materials science. In the last few years, [2.2]paracyclophane chemistry has progressed tremendously, enabling the fine‐tuning of its structural and functional properties. This Minireview highlights the most important recent synthetic developments in the selective functionalization of PCP that govern distinct features of planar chirality as well as chiroptical and optoelectronic properties. Special focus is given to the function‐inspired design of [2.2]paracyclophane‐based π‐stacked conjugated materials by transition‐metal‐catalyzed cross‐coupling reactions. Current synthetic challenges, limitations, as well as future research directions and new avenues for advancing cyclophane chemistry are also summarized.
Highlights
Introduction andHistory parylene coatings.[14]
New methods of CÀH functionalization at the PCP backbone with excellent selectivity and improved reactivity to install a broad range of functionalities are very much desired goals, but are yet to be discovered
Investigation of the PCP derivatives as chiral ligands in asymmetric catalysis has been one of the most active areas so far; this scaffold with its key features of a rigid, chiral, and stable building block is emerging in other fields of research as it possesses manifold applications that are to be explored
Summary
Disubstituted PCPs are accessible starting from monosubstituted PCP. The mechanisms of the regioselective electrophilic aromatic substitution reactions of PCPs and their interconversions were investigated by Cram and Reich.[3]. [2.2]Paracyclophanes containing halides and pseudohalides represent versatile modular molecular building blocks in the design and development of hole-transporting materials[77] and helically structured chiral macrocycles.[78] These building blocks can be incorporated into numerous p-stacked conjugated polymers to introduce the innate physical/chemical properties of PCP such as their planar chirality and layered structure.[79] As Figure 6 illustrates, the Suzuki–Miyaura, Sonogashira–Hagihara, and Mizoroki–Heck reactions are the most common Pd-catalyzed coupling routes for the assembly of p-stacked conjugated polymers containing iodo-, bromo-, vinyl-, ethynyl-, and formyl-substituted [2.2]paracyclophanes as key components in their skeleton.[80] Structurally different PCP derivatives such as pseudo-geminal- (44), pseudo-para- (45), and pseudo-ortho-dibromo[2.2]paracyclophane (46) allow the construction of various p-stacked conformations such as linear, zig-zag, and fully stacked structures.
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