The Scholl Reaction as a Powerful Tool for Synthesis of Curved Polycyclic Aromatics

Abstract

The past decade has witnessed remarkable success in the synthesis of curved polycyclic aromatics through Scholl reactions which enable oxidative aryl–aryl coupling even in company with the introduction of significant steric strain. These curved polycyclic aromatics are not only unique objects of structural organic chemistry in relation to the nature of aromaticity but also play an important role in bottom-up approaches to precise synthesis of nanocarbons of unique topology. Moreover, they have received considerable attention in the fields of supramolecular chemistry and organic functional materials because of their interesting properties and promising applications. Despite the great success of Scholl reactions in synthesis of curved polycyclic aromatics, the outcome of a newly designed substrate in the Scholl reaction still cannot be predicted in a generic and precise manner largely due to limited understanding on the reaction mechanism and possible rearrangement processes. This review provides an overview of Scholl reactions with a focus on their applications in synthesis of curved polycyclic aromatics with interesting structures and properties and aims to shed light on the key factors that affect Scholl reactions in synthesizing sterically strained polycyclic aromatics.

Aggregation-Induced Emission of Contorted Polycondensed Aromatic Hydrocarbons Made by Edge Extension Using a Palladium-Catalyzed Cyclopentannulation Reaction

“…Desired compounds CPA1 30 CPA2, CPB1−2 were isolated in excellent yields (86−90%) and have excellent solubility in common organic solvents. It is noteworthy that the formation of CPA2 and CPB1−2 was confirmed by 1 Figure 1 portrays the comparative 1 H-NMR spectra of both synthons TPE and DBBA in addition to target PAH CPB1, which clearly confirms the presence of all the desired peaks for the latter and the absence of those of the starting material. Thus, the aromatic protons of CPB1 were detected in the range of 7.8−7.0 ppm (see Figure 1 and Figure S3 in the Supporting Information).…”

“…The combined organic layer was washed with deionized water (50 mL × 3) and concentrated, and the product was purified by silica gel column chromatography using DCM/hexane (50:50 v/v) as the eluent affording a green solid (45 mg, 90%). 1 Synthesis of 1,1′-Bis(4-(tert-butyl)phenyl)-2,2′-di-(naphthalen-1-yl)-6,6′-biaceanthrylene CPB2. CPB2 was prepared following procedure A with 10,10′-dibromo-9,9′-bianthracene DBBA (36 mg, 0.07 mmol, 1 equiv), TPEN (44 mg, 0.15 mmol, 2.2 equiv), Pd 2 (dba) 3 (6.4 mg, 7.0 μmol, 0.1 equiv), P(o-tol) 3 (2.1 mg, 7.0 μmol), KOAc (34 mg, 0.35 mmol), and LiCl (5.9 mg, 0.14 mmol).…”

“…Contorted polycyclic aromatic hydrocarbons (PAHs) are conjugated compounds whose out-of-plane geometry is mostly caused by an intramolecular steric congestion. , PAHs bearing cyclopentadienide units, which can be considered as cross-sectional units of fullerenes, disclose prominent optoelectronic − properties and, consequently, are employed in organic field-effect transistors (OFETs), organic light emitting diodes (OLEDs), and organic photovoltaics (OPVs). , Thus, there is a growing interest in exploring versatile and efficient synthetic strategies to make new contorted PAH structures and explore their chemical and physical properties . Among others, palladium- and nickel-catalyzed cross-coupling reactions, notably, Heck, Negishi, Suzuki–Miyaura, and Sonogashira, , are widely utilized in the synthesis of PAHs. − In addition, cycloaddition reactions have traditionally been used in the synthesis of large PAHs, namely, Diels–Alder reaction, which proved to be a versatile synthetic approach to make large aromatic compounds .…”

Iron-Catalyzed C–H Activation for Heterocoupling and Copolymerization of Thiophenes with Enamines

“…We first note that the enamines reactive in the present reaction are not very basic, being conjugated with the neighboring aromatic groups. We noted that only the acetaldehyde enamines produce the desired product in 39− 90% yield (Figure 3c, 5−9), whereas enamides (10−12), substituted enamines (13−16), and enol ethers (17,18) gave little or no desired product (Figure 3d). The steric hindrance imposed by the carbazole moiety in 2 may be important in that it allows only the vinyl part of the enamine to interact with the sterically congested Fe(III)/TP1 center.…”

“…16 Compound 34 showed intense fluorescence in the blue-green region with a quantum yield of Φ FL = 0.84. The tetraphenylbenzene moiety found in 36 is a prototypical substrate for the oxidative Scholl cyclization, 17 yet it survived well under our mild conditions. The reaction of 2,7-and 3,6-diarylated N-vinylcarbazoles afforded highly conjugated vinylene products (37,38).…”