Sequential Tether‐Directed Synthesis of Pentakis‐Adducts of C₆₀ with a Mixed [3:2] Octahedral Addition Pattern

Abstract

The design of a novel concept for the synthesis of [3:2] pentakis‐adducts of fullerene C60 is presented. A sequential tether‐directed, remote functionalization approach is introduced for the construction of the pentakis‐adducts. This fullerene derivative embellished with two different addends in two different directions can be considered as a valuable tecton for further functionalization. The stepwise cyclopropanation of C60 with a macrocyclic tris‐malonate and a bis(β‐keto ester) yielded the corresponding pentakis‐adduct with an incomplete octahedral addition pattern. This reaction sequence gave access to two pairs of enantiomers that were easily separated by column chromatography on an achiral stationary phase and subsequently characterized.

Supramolecular Fullerene Sponges as Catalytic Masks for Regioselective Functionalization of C60

“…18 To address this shortcoming, different strategies for the selective production of multiple substituted fullerenes have been pursued, generally involving the initial stoichiometric modification of the fullerene with directing groups. Highlighted is the ''tether-directed remote functionalization'' strategy for the synthesis of bis-, tris-, pentakis-, and hexakis-adducts under regiocontrol, firstly developed by Diederich in 1994 (Figure 1A), [19][20][21][22][23] and the ''orthogonal transposition'' synthetic strategy developed by Krä utler in 1997 (Figure 1B) 24 for the production of the equatorial-cyclopropanated tetrakis-diethylmalonate-C 60 adduct (Bingel-Hirsch reaction), which is used for further functionalization on the available axial positions. 25 On the other hand, the modulation of the C 60 regiochemical reactivity by confinement in supramolecular receptors remains scarce.…”

Sequential Tether‐Directed Synthesis of New [3 : 2 : 1] Hexakis‐Adducts of C60 with a Mixed Octahedral Addition Pattern

“…Cyclopropanation reactions with flexible cyclo ‐[n]‐ alkyl malonate macrocycles as tether‐directing agents resulted in a variety of oligo‐adducts with rotational symmetry, such as C 3v ‐symmetrical e , e , e ‐tris‐adduct 1 (Figure 1) with a semioctahedral addition pattern [5] . Recently, the sequential addition of a trifunctional and a bifunctional tether to C 60 provided access to four stereoisomers of [3 : 2] pentakis‐adduct 2 in excellent regioselectivity [6] . However, isolation of the stereoisomers was reported to be difficult and only the two diastereomers of 2 , which differ in the orientation of the bis(β‐keto ester) addend (Figure 1), could be separated [6] …”

“…To date the exohedral functionalization of fullerene C 60 is the most commonly applied method for chemical modifications of this fullerene core. The thirty [6,6] double bonds on the spherical surface of C 60 facilitate a variety of functionalizations via single or multiple addition and cycloaddition reactions. [1] However, the first attempts of synthesizing fullerene bisadducts without further control of regioselectivity resulted in seven of eight theoretical regioisomers.…”

Supramolecular Fullerene Sponges As Catalytic Masks for Regioselective Functionalization of C ₆₀

“…Highlighted are the "tether-directed remote functionalization" strategy for the synthesis of bis-, tris-, pentakis-and hexakis-adducts under regiocontrol, firstly developed by Diederich in 1994 (Fig. 1a), [8,11,[13][14]26] and the "orthogonal transposition" synthetic strategy developed by Kräutler in 1997 (Fig. 1b), [12] for the production of equatorial cyclopropanated tetrakis-diethylmalonate-C60 adduct (Bingel-Hirsch reaction), which is used for further functionalization on the available axial positions.…”

“…single isomer poly-functionalized fullerenes are only accessible via stoichiometric, multistep paths entailing protecting-unprotecting sequences. [8][9][10][11][12][13][14] Herein, a nanocapsule is used as a supramolecular mask to exert full control on the reactivity and the equatorial regioselectivity of Bingel-Hirsch cyclopropanation reactions of confined fullerene guests. Thus, equatorial bis-, trisand tetrakis-C60 homo-adducts are exclusively obtained in a stepwise manner, completely avoiding over functionalization (always observed in bulk solution) and holding precise control on the number of additions.…”