Fullerene fragments

It is reported that the palladium-catalysed intramolecular aromatization of 1,1 -dichloro-9/T-fluoren-9-yIidene (15) may lead to the formation of fullerene fragments.89 The amiulation reaction, under palladium catalysis, between iodoanflines and ketones may yield indole derivatives.90 There have also been studies of the palladium-catalysed carbonylation of o-iodophenols with allenes which may lead to l-benzopyran-4-one derivatives,91 of the intramolecular coupling of phenols with aryl halides,92 and of the intramolecular Heck aiylation of cyclic enamides.93... 

CONTENTS Preface, Brian Hatton. Applications of Ring Strain in Natural Product Synthesis, James D. White and Nadine Chauyi Lee. Uses of the Vacuum Gas-Solid Reaction Procedure in Synthesis, W. E. Billups and Benny E. Amey, Jr. Polysubstituted Cubanes Towards Complete Systematic Substitution of the Cubane Nucleus, John Tsanaktsidis. A Personal Perspective on Norbomenes, Cyclobutenes, and Other Ring-Strained Dienophiles in Organic Synthesis, Ron N. Warrener. Synthetic Studies Related to Fullerenes and Fullerene Fragments, Goverdhan Mehta and H. Surya Prakash Rao. Index. 

Expanding our search to fullerene fragments we investigated the potential host-guest chemistry of the nanotubes with polyaromatic hydrocarbons shown in Fig. 34 [30],... 

This method has been applied to the synthesis of various polycyclic aromatic compounds [91]. Among the interesting applications are lactone formation in the preparation of natural products having biaryl skeletons (Eq. 42) [87] and double cyclization leading to spirocyclic compounds (Eq. 43) [92] and a fullerene fragment (Eq.44) [93]. 

The [2-1-1] fragmentation of the precursors shown in Figure 6.2 also provides a potential route to monocyclic carbon clusters. Thus cyclic dehydro oligomers of diethynyl[4.4.1]propellatetraenes 6a,b incorporated in a fullerene structure have been prepared and their fragmentation was investigated by mass spectrometry [7]. MALDI TOF mass spectra of 6a,b exhibited peaks due to the stepwise loss of the fullerene fragments, leading to the formation of mono-fullerene adducts of C15 and C20. However, the... 

If the [ 6] electrocyclization is impeded for steric or electronic reasons, the yields of thermal cyclodehydrogenation reactions normally decrease to a few or even less than one percent [38-41]. Nevertheless, the interesting bowl-shaped fullerene fragments diindeno[l,2,3,4-de/g l, 2, 3, 4 -mz70p]chrysene (6, [38d,e]) and triacenaphtho[3,2,l,8-cdejg 3, 2, l, 8 -zjk/m 3",2",r, 8"-opqra]triphenylene (7, [39]) could be obtained from 4 and decacyclene (8), respectively, for the first time (see Scheme 3). 

Scheme 3. Syntheses of bowl-shaped fullerene fragments by thermal cyclodehydrogenation using the flash vacuum pyrolysis methodology [38,39]...

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... 

As a dibenzo analogue of 19 and a pen-benzoannelated diindane (cf. 4), flu-oradene (26) is considerably strained [56], as is pyracyclene (27) [57]. Truxene (29), the parent polyindane of truxenequinone and related well known condensates of 1,3-indanedione, is essentially planar, but has been used as a basis for approaching fullerene fragments by synthetic means [13,14,58,59]. Coran-... 

This is indeed close to reality as actually hemispheric caps are observed rather seldom. In most cases conical structures are found. These bear defects at the tip itself as well as at the transition to the nanotube. They aU have in common that the required curvature is brought about by pentagonal defects. The bevel angle of such conical caps depends on the number of five-membered rings present at their tips, as demonstrated by the values in Table 3.1. A cap with six pentagonal defects, for instance a hemispheric fullerene fragment, enables a direct transition to the tubular part, while a smaller number of five-membered rings causes a more or less conical shape. 

Dibenzo[a, ]corannulene (116), a fullerene fragment, was obtained by cycliza-tion of 7,10-di(2-bromophenyl)fluoranthene (115). A Herrmann palladacycle (XVIII-1) as a catalyst and excess DBU as a base were used under rather severe conditions (150" C, 72 h) [32], Also the as -indaceneo[3.2.1.8.7.6-pqrstuv]picene derivative 118 was prepared from the dichloride 117 in 91% yield. PCyg and DBU were used for activation of the less reactive dichloride 117 [33]. 

Complexation of metals to curved carbon n surfaces has attracted continuous interest since the discovery of fullerenes. So far, fullerenes have been found to act as an -coordination ligand to various transition metals from its eYO- r-surface [1, 2], Other coordination modes in exo complexes were reported in the modified fullerene it systems [3], such as buckyferrocene [4] Fe(CgoMe5)Cp (Cp = cyclopentadienyl). Fullerenes are also known to form the endohedral metal complexes to provide potential materials in carbon chemistry [5, 6], On the other hand, fullerene fragments, termed as n bowls (we use this term in the present chapter, whereas they have been also called open geodesic polyarenes [7] or buckybowls [8]), also possess curved carbon n surfaces, n Bowls have attracted interest in the science of nonplanar -conjugated carbon systems [9-14], From the viewpoint of coordination chemistry, such molecules are quite unique because they can provide not only a convex surface but also an open concave surface for binding (a schematic illustration is shown in Fig. 35.1), which was first addressed by the computational study of hemifullerene (C30H12) in 1993 [15],... 

With this assumption at hand, it is possible to obtain the evolution of the translational, rotational and vibrational contributions to the energy of the fullerene fragments, as well as the emitted dimers. In particular, from the respective distributions the corresponding temperatures can be inferred by appropriate fltting onto Boltzmann forms. Figure 4.8 shows the variations of the three temperatures of carbon dimers emitted successively from after a... 

Recent examples featuring acenaphthylene moieties are included in this section. In general, Pd-catalyzed methods of constructing the CPPAs have overtaken traditional annulations and the harsh conditions of flash vacuum pyrolysis. Readily available haloarenes and reliable synthetic procedures have allowed the preparation of these planar fullerene fragments. Study of the compounds has brought to light some of the defining properties of CPPAs and how the desirable traits of fullerenes can be expressed in small molecules. 

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