Corannulene synthesis

Other deliberate steps out of the plane, into three-dimensional space were also undertaken in the 1960s (see the corannulene synthesis by Lawton and Barth 1966). The real death blow to planar thinking, which is just another word for rigid thinking, came with the fullerene work of Kroto, Smalley, Kratschmer, and many others. I am sure that even Kekule would have called these results new. ... 

The preceding section indicated the importance of corannulene as the smallest member of the family of bowl-shaped, polynuclear aromatic hydrocarbons modeling the surface of buckminsterfullerene. Surprisingly, despite its obvious significance in relationship to the theory of aromaticity, 8 had not attracted the attention of chemists prior to the first report of its synthesis in 1966." As Barth and Lawton noted ... to the time of our first report, it appears this structure had neither adoriied the jacket or end cover of any book nor served as a symbol of an international symposium. More than that, corannulene does not appear to have been suggested in the chemical literature prior to 1966. 

Two years later, Craig and Robinson attempted an alternative synthesis of 8 with a more symmetrical pathway starting from derivatives of fluoranthene. Cycliza-tion of fluoranthene-7,10-diacetic acid 14 was attempted to produce diketone 15, expected to enolize to the dihydroxycorannulene 16. Unfortunately, several attempts at cyclization failed, including anhydrous hydrofluoric acid, concentrated sulfuric acid, and polyphosphoric acid. Friedel-Crafts cyclization of the corresponding acid chloride of 14 with aluminum or stannic chloride was similarly unsuccessful. However, although Craig and Robinson were not successful, they developed a convenient synthesis of 7,10-disubstituted fluoranthenes which turned out later to be of premium importance in a new, successful synthesis of corannulene. 

An alternative synthesis of corannulene, also involving a pyrolysis, was reported by Siegel and co-workers (Scheme 4), The tetrabromide may be directly pyro-lyzed to corannulene, or it may be converted to a bis-sulfone where extrusion of SO2 produces a mixture of 8 along with its di- and tetrahydro derivatives, and 5,6-dimethy 1-benzo [g/ir] fluoranthene. 

Dihydtocorannulene (21) and tetrahydiocorannulene (22) were first produced as side products in the synthesis of corannulene (see Scheme 4). These structures retain the general bowl shape, and NMR inversion barriers were estimated to be 8.5 and 7 kcal/mol, respectively. Dihydrocorannulenes can also be produced by the addition of alkyllithiums to corannulene to afford 1-alky 1-1,2-dihydrocoran-nulenes (21 ). ... 

The first synthesis of a semibuckminsterfullerene was accomplished by a procedure analogous to the preparation of corannulene except that 1,2,5,6-tetrake-topyracene served as the starting material (Scheme 5). Flash vacuum pyrolysis of the tetrachloro compound led to a remarkable quadruple ring closure to produce the semi-buckminsterfullerene 27. The NMR shows three methine carbons and five quaternary carbons at 125.5, 126.8, 127.3, 128.6, 136.7, 137.3, 142.0, and 145.4 ppm. The latter signals compare favorably to the single resonance observed at 143 ppm for buckminsterfullerene. 

There have been several developments in this area since this manuscript was prepared. The heat of combustion of corannulene was determined by microbomb combustion calorimetry and its gas-phase enthalpy of formation was estimated at 110.8 kcal/mol. All anionic oxidation states of corannulene were observed by optical absorption, EPR, and NMR spectroscopies. More support for the an-nulene-within-annulene model of the corannulene tetraanion was presented. An alternative pyrolysis route to corannulene was reported, as well as some attempts toward the synthesis of bowl-shaped subunits of fullerenes. And in contrast with previous semiempirical studies," ab initio calculations predicted a general concave preference for the metal cation binding to semibuckminsterfullerene 2%. ... 

The iron-mediated [2 + 2 + 1]-cycloaddition to cyclopentadienones has been successfully applied to the synthesis of corannulene [24] and the yohimbane alkaloid ( )-demethoxycarbonyldihydrogambirtannine [25]. A [2 + 2 + l]-cydoaddition of an alkene, an alkyne and carbon monoxide mediated by pentacarbonyliron, related to the well-known Pauson-Khand reaction [26], has also been described to afford cyclopentenones [27]. 

Our goal in those days was to find a new Jt-system more aromatic than king benzene. Then came the news of the corannulene (6) synthesis by Barth Lawton (1966) and its bowl-shaped structure quickly aroused strong interest among us. As is mentioned below, analysis of its structure logically led us to conceive the extrapolation of its structure to a sphere so that we could envisage three-dimensional delocalization of the 7t-electrons. Fortuitously about that time my small son started... 

Corannulene, C2oH10, dibenzo y/ /, mno] fluoranthene, shown in Fig. 1(a), is a bowl-shaped PAH with 5-fold symmetry [6], and has a one-third skeleton of C60 (see Figs 1(c) and (d)). Recently, convenient synthesis for corannulene [7,8] has been developed. On the other hand, coronene, C24H12, hexabenzobenzene, shown in Fig. 1(b), has a flat structure with a 6-fold symmetry axis. 

Synthesis of the p-phenylene-bridged dibenzo-fused corannulene C60Me5Ph3H2 (10) To a solution of 4 (40 mg, 38 pmol) in PhCN (10 mL) in a Schlenk tube was added a solution of lithium naphthalenide (1.5 mL, 0.76 M in THF, 1.1 mmol) under an argon atmosphere. The color of the solution changed immediately from yellow to... 

In Chapter 2, Matsuo and Nakamura describe the synthetic developments of a subgroup of bowl-shaped it-conjugated corannulenes and expand the topic to the discussion of the synthesis of a novel class of organic fluorophores derived from C60, hoop-shaped condensed aromatic compounds. They are made by selective removal of ten sp2 carbon centers out of conjugation from the north and south pole regions of C60. The resulting 40-jr-electron [lOjcyclophenacenes excised... 

Siegel s group is the synthesis of the first coran-nulene cyclophane 80 [56]. A striking feature of its H NMR spectrum is that the endo aromatic protons (Hj.) of the benzene ring, which are positioned almost directly over the center of the corannulene system, appear at remarkably high field ( =1,89). Furthermore, with no peak broadening up to 148 °C, it was established that dynamic conformational processes in the thioether bridges and bowl-to-bowl inversion of the corannulene moiety both have lower limits of 18 1 kcal mol . ... 

Numerous aromatic compounds including several bowl-shaped fullerene fragments have been prepared by this method, e.g. cyclopenta[z/]fluoranthene (22, Scheme8, [54d,56a]), cyclopenta[bc]corannulene (23, [55a]) and diace-naphtho[3,2,l,8-cdejg 3, 2, l, 8 -Zmnop]chrysene (24, see Scheme 9, [55b,c]). Of special importance is this approach for the synthesis of cyclopenta-annelated PAHs, e.g. and the three isomeric dicyclopentapyrenes (25-27, Scheme 9, [54e, 56b]). Using these reference samples, several cyclopenta-annelated PAHs could be identified as byproducts formed in the incomplete oxidation of hydrocarbons in fuel rich flames [57]. 

Low valent titanium reagents have been used in the first low temperature synthesis of the fullerene fragment dimethyl corannulene (53) from the 1,6-bis(bromomethyl)-7,10-bis(l-bromoethyl)fluoranthene (54, see Scheme 24 [107]). Obviously, the high thermodynamic driving forces for the reductive elimination of bromine as well as for the aromatization with 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) in the course of the reaction via the relatively unstrained a s/frans-dimethyltetrahydrocorannulenes enabled the formation of... 

Liu P, Hisamune Y, Peeks MD, et al. Synthesis of five-porphyrin nanorings by using ferrocene and corannulene templates. Angew Chem Int Ed. 2016 55 8358-8362. 

One of the most intriguing applications of this reaction occurs in Scott s pyrolytic synthesis of corannulene, which is one-third of C q, from 7,10-diethynylfluor-anthene (Scheme 7.25). ... 

Bowl-shaped carbocations (33) were obtained by alkylation of the parent corannulene. ° The cations were obtained as stable salts and characterized by X-ray analysis. Phenalenyl cations (e.g. (34)) were obtained as air-stable BPh4 salts. Observations made in a selective synthesis of l,2-di(organo)fullerenes led to a mechanism whereby a cationic fullerene intermediate is generated by Cu(ll) oxidation of a fullerene radical (or anion). ... 

The chemistry of corannulene-based [4—12] and sumanene-based buckybowls [4, 12-15] has been described in several review articles. In 2006 we published a review article focusing on the solution-phase synthesis of buckybowls, and the structures and physical properties of compounds thus prepared [7]. Since then, this research field has expanded dramatically and many important results have appeared we update the contents herein, and introduce some important compotmds, which are not famished by solution-phase synthesis. Due to page limitations, some... 

Corannulene (1) was synthesized by Lawton and Barth in 1966 [17, 18]. As mentioned by them Within its structural framework is an unusual strain resulting from the geometrical requirement that the bond angles deviate appreciably from the normal values found for benzenoid compounds. Thus, introduction of strain as late as possible is key to their synthetic strategy for the preparation of 1 [19]. Their synthesis started with acenaphthene, and after numerous synthetic steps the key intermediate 4 was obtained (Scheme 1). The diol acid 4 was converted to 5 upon... 

Scheme 1 Synthesis of corannulene (1) based on Lawton and Barth s procedure [17, 18]...

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