Synthesis and Orthogonal Functionalization of [60]Fullerene e,e,e‐Trisadducts with Two Spherically Defined Addend Zones

Abstract

e,e,e-Trisadducts 13 and 15 have been prepared by a highly regioselective threefold cyclopropanation of tripodal malonates 10 and 12 with C60. The yield and regioselectivity depend on the length and structure of the tethers that connect the malonate units to the focal benzene core of 13-15. As a consequence of the template-directed synthesis, all e,e,e-trisadducts were formed as in/out isomers exclusively and contain two spherically well-defined addend zones with equatorial and polar orientation, respectively. By variation of the outer malonate termini of the tethers, selective functionalization of the equatorial addend zone could be achieved, thus leading to fine-tuning of intermolecular interactions, such as solubility or aggregation phenomena. After removal of the focal benzene moiety in 14 and 15, selective functionalization of the polar addend zone could be achieved. Strong intramolecular hydrogen-bonding networks of the polar substituents in the polar addend zone could be observed by 1H NMR spectroscopic analysis. By orthogonal functionalization of both addend zones, fullerene derivatives 44-48 could be synthesized as one single in/out isomer, thus greatly enhancing the potential of e,e,e-trisadducts as building blocks in supramolecular architectures.

Facile Access to Functional Building Blocks of C60 Involving C3‐Symmetrical Addition Patterns

“…After purification by column chromatography, the product was determined to be trisbromo derivative 12 by mass spectrometric and NMR spectroscopic analysis. The same compound had been generated previously from the corresponding benzene templated trisadduct, demonstrated by spectroscopic data 10b. Additional experiments showed that neither TMSBr, nor DBU alone caused deprotection.…”

Regioselectivity in Tether‐Directed Remote Functionalization – The Addition of a Cyclotriveratrylene‐Based Trimalonate to C60 Revisited

“…[19] Racemic, C 3 -symmetrical adducts of C 60 with the inherently chiral e,e,e addition pattern were obtained by Hirsch and co-workers through addition of achiral tripodal conjugates having trimalonates linked to a benzene-1,3,5-trimethylene or a benzene-1,3,5-trioxy core. [28,29] Addition of the macromonocycle tris(octamethylene) cyclotrimalonate to C 60 provided the C 3 -symmetrical e,e,e tris-adduct in high yields, and the achiral C 3v -symmetrical trans-4,trans-4,trans-4 derivative as a minor product. [30] A chiral cyclotrimalonate with enantiomerically pure spacer units derived from -mannitol afforded C 3 -symmetrical adducts in a 4:1 ratio as separable diastereoisomers with enantiomeric e,e,e fullerene addition patterns.…”

A study towards the regioselective synthesis of the e,e,e trisadduct of C60 via the [4+2] Diels-Alder reaction with tethers bearing ortho-quinodimethane precursors

“…The tether-directed remote functionalization method has been successfully applied for the synthesis of C 3 -symmetrical trisadducts of C 60 by the groups of Diederich, 6 Hirsch, [7][8][9][10][11][12] Nierengarten 13-15 and ours. [16][17][18] Opened-and closed-structure tethers equipped with three malonate groups were utilized for this purpose and all possible C 3 -symmetrical addition patterns have been accessed except the cis-1,cis-1,cis-1 (all-cis-1) which is not energetically favored owing to the steric hindrance of the addends.…”

“…The reports of Hirsch [9][10][11][12] and Nierengarten 13,14 on the synthesis of e,e,e trisadducts of C 60 with tripodal tethers equipped with malonate moieties, prompted us to design opened-structure tether 10 bearing ortho-quinodimethane precursors covalently connected to the phloroglucinol focal point via two-carbon alkyl chains (Scheme 3). Bromoethanol was firstly protected as a THP ether 33 followed by a three-fold Williamson etherification with phloroglucinol to afford tripodal protected alcohol 7.…”