Regio‐ and Stereoselective Multiple Functionalization of Fullerenes

Abstract

The synthesis of multiple adducts of CW has attracted much attention in recent years [ 11.Investigations of covalent derivatives with varying degrees and patterns of addition make it possible to explore how characteristic fullerene properties are affected by functionalization-induced changes in the conjugated n-chromophore [2]. Furthermore, higher adducts of c 6 0 represent an unprecedented family of three-dimensional building blocks for molecular scaffolding targeting advanced fullerene materials and technologies [3]. The direct sequential multiple functionalization of the carbon sphere, however, is problematic in most cases, and isolation of a pure higher adduct usually requires tedious chromatographic isomer separation [4-61. Moreover, a great diversity of interesting addition patterns is not accessible by sequential derivatization. Therefore, we proposed in 1994 a more general approach to the regioselective formation of multiple adducts of c 6 0 by taking advantage of tether-directed remote functionalization techniques [7]. Such strategies had been initially developed by Breslow and co-workers for the selective functionalization of steroids and long-chain alkanes (see Chapter 6 ) [8]. Here, we illustrate how the application of non-covalent and covalent templates provides access to a great diversity of three-dimensionally functionalized fullerene building blocks. Templated synthesis now serves as a powerful tool for chemists interested in exploiting the outstanding technological potential of fullerenes and their covalent derivatives. Anthracenes as Reversible Covalent TemplatesAmong the most versatile reactions in fullerene chemistry is the Bingel cyclopropanation with 2-bromomalonate in the presence of base [9]. The problematics of regioisomeric product formation in nucleophilic additions to C,, is illustrated in the following, using this reaction as an example. By sequential double Bingel addition, Hirsch and co-workers obtained seven (1-7) out of eight possible bis-adducts named as cis-1-3, eface and edge (these two bis-adducts are identical if the two addends are identical), and truns-I -4 (Scheme 7-1) [lo, 111, which could be separated by high-performance liquid chromatography (HPLC). Only the cis-1 bis-adduct was not formed in detectable quantities due to steric interactions between the addends which are forced into close proximity. The e (3) and trans-3 (5) bis-adducts are the major products in the sequential double addition,

Synthesis and Characterization of Mono- and Bis-methano[60]fullerenyl Amino Acid Derivatives and Their Reductive Ring-Opening Retro-Bingel Reactions

“…In principle, the bis-cyclopropanation of [60]fullerene using tethered bis- N -(diphenylmethylene)glycinate esters followed by our reductive ring-opening methodology would allow protected bis-amino acid functionalities to be incorporated into precise locations on the surface of the fullerene sphere. To produce regioselective multifunctionalized fullerenyl amino acids, a tether-directed methodology was adopted. , The tethers chosen for bisfunctionalization of [60]fullerene were the benzenedimethanols 23 − 25 that have been used extensively by the Diederich group for the malonate-derived biscyclopropanation of [60]fullerene . The tethered bis- N -(diphenylmethylene)glycinate diesters 32 − 34 were synthesized as shown in Scheme .…”

“…The pioneering investigations into the chemical reactivity of [60]fullerene − have provided a precedent toward the design and synthesis of novel and sophisticated architectures that may have applications in medicinal chemistry and the material sciences. − The incorporation of biomolecular principles (such as water solubility and precise secondary/tertiary structure) with the unique physicochemical properties of fullerenes (sensitization of singlet oxygen; electron acceptor characteristics) have produced molecular structures with a variety of biological activities . For example, in 1993, Friedman and co-workers recognized the fullerene sphere can be accommodated inside the cylindrical hydrophobic cavity of HIV protease .…”

Interaction of C60 Derivatives and ssDNA from Simulations

“…The third is to introduce hydrophilic function groups such as amino or hydroxyl groups . C 60 has been known to have a relatively high reactivity that allows various structural modifications. , Therefore, the last approach serves as a versatile methodology that leads to a wide variety of C 60 derivatives with different physical and chemical properties. , …”

Unexpected Change in Charge Transfer Behavior in a Cobalt(II) Porphyrin−Fullerene Conjugate That Stabilizes Radical Ion Pair States

“…The coupling of porphyrins and fullerenes is a theme of considerable current interest, given the potential applications of the photochemistry peculiar to the resulting systems in photovoltaic devices and optical limiting and molecular electronics . Methods exist for synthesizing porphyrins with an almost unlimited range of functionality and regiochemistry (albeit sometimes in complex mixtures and low yield); together with the emerging diversity of reliable and regioselective methods for functionalizing fullerenes, the possibilities for tuning photochemical properties in such conjugates are numerous, to say the least.…”