A photochemical approach to aromatic extension of the corannulene nucleus

Abstract

A high yielding, general, and mild synthetic strategy is established for aromatic annulation of the corannulene scaffold. In this approach, a corannulene-based aldehyde, ylide, or ketone compound is conjugated with an aromatic unit of choice through a Wittig reaction. The resulting stilbene-like precursor can be subjected to a photochemically induced oxidative-cyclization process to yield a corannulene structure with an extended π-framework. The generality of synthesis allows for preparation of a wide range of polycyclic aromatic arene as well as heteroarene structures. Meanwhile, the mild nature of the developed protocol permits for incorporation of reactive and functional substituents onto the fused aromatic scaffold. Furthermore, efficient and simple synthesis ensures access to significant amounts of the material in a facile manner. In essence, this work demonstrates, for the first time, that photochemical synthesis is a highly practical alternative to the known flash vacuum pyrolysis and metal catalyzed processes for the aromatic extension of the bucky-bowl structure.

Synthesis and Properties of Large Polycyclic Aromatic Hydrocarbons with Planar and Non‐Planar Structural Motifs

“…To accomplish the synthesis of the aforementioned structures, corannulene‐based phosphonium ylide 1 and commercially available pyrene aldehyde 2 were subjected to a Wittig reaction (Scheme ) . This afforded the stilbene‐like molecule 3 in which the C=C bond is flanked by both aromatic units.…”

“…This afforded the stilbene‐like molecule 3 in which the C=C bond is flanked by both aromatic units. A subsequent photochemically induced oxidative cyclization process then enabled fusion of the aromatic systems to create the large π‐extended structure 4 , . The stilbene formation and the annulation process proceeded with isolated yields of 75 and 78 %, respectively.…”

“…High resolution MALDI-TOF mass analysis reveals the parent ion peaks at m/z = 476.1513 (calculated for C 38 H 20 The UV/Vis absorption spectra of the individual components corannulene, pyrene, and the hybrid structures 3 and 4, are starkly different ( Figure 3). In general, a bathochromic shift of more than 100 nm was observed upon combination of both structural motifs into one structure.…”

“…Synthesis of 3: To a vacuum‐dried round‐bottom flask containing a suspension of corannulenylmethyl triphenylphosphonium bromide 1 (400 mg, 0.66 mmol, 1 equiv.) in 20 mL of dry THF was added n BuLi (2.5 m solution in hexane, 0.396 mL, 1.5 equiv.)…”

“…Weinheim 6013 ide[20] 1 (400 mg, 0.66 mmol, 1 equiv.) in 20 mL of dry THF was added nBuLi (2.5 M solution in hexane, 0.396 mL, 1.5 equiv.)…”