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Herrmann, Andreas; Rüttimann, Markus; Gibtner, Thomas; Thilgen, Carlo; Diederich, François; Mordasini, Tiziana; Thiel, Walter

doi:10.1002/(sici)1522-2675(19990210)82:2<261::aid-hlca261>3.3.co;2-o

Cited by 16 publications

(91 citation statements)

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“…Double Bingel cyclopropanations of C 70 with diethyl malonate occur on opposite hemispheres at the most curved a-type bonds, yielding the three constitutional isomers 2, (AE)-3, and (AE)-4, two of which are pairs of enantiomers due to the chirality of the addition pattern [5] [6] [14]. The isomeric ratio 2/(AE)-3/(AE)-4 is 2.8 : 6.8 : 1.0.…”

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confidence: 99%

Supramolecular Fullerene Chemistry: A Comprehensive Study of Cyclophane-Type Mono- and Bis-Crown Ether Conjugates of C70

Eis

Seiler

Muslinkina

et al. 2002

HCA

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A Corun ƒ a Dedicated to Professor Friedrich Bickelhaupt on the occasion of his 70th birthday.The covalently templated bis-functionalization of C 70 , employing bis-malonate 5 tethered by an antidisubstituted dibenzo [18]crown-6 (DB18C6) ether, proceeds with complete regiospecificity and provides two diastereoisomeric pairs of enantiomeric C 70 crown ether conjugates, (AE)-7a and (AE)-7b, featuring a five o×clock bis-addition pattern that is disfavored in sequential transformations (Scheme 1). The identity of (AE)-7a was revealed by X-ray crystal-structure analysis (Fig. 6). With bis-malonate 6 containing a syn-disubstituted DB18C6 tether, the regioselectivity of the macrocylization via double Bingel cyclopropanation changed completely, affording two constitutionally isomeric C 70 crown ether conjugates in a ca. 1 : 1 ratio featuring the twelve (16) and two o×clock ((AE)-15) addition patterns, respectively (Scheme 3). The X-ray crystal-structure analysis of the twelve o×clock bis-adduct 16 revealed that a H 2 O molecule was included in the crown ether cavity (Figs. 7 and 8). Two sequential Bingel macrocyclizations, first with anti-DB18C6-tethered (5) and subsequently with syn-DB18C6-tethered (6) bis-malonates, provided access to the first fullerene bis-crown ether conjugates. The two diastereoisomeric pairs of enantiomers (AE)-28a and (AE)-28b were formed in high yield and with complete regioselectivity (Scheme 9). The cation-binding properties of all C 70 crown-ether conjugates were determined with the help of ion-selective electrodes (ISEs). Mono-crown ether conjugates form stable 1 : 1 complexes with alkali-metal ions, whereas the tetrakis-adducts of C 70 , featuring two covalently attached crown ethers, form stable 1 : 1 and 1 : 2 host-guest complexes ( Table 2). Comparative studies showed that the conformation of the DB18C6 ionophore imposed by the macrocyclic bridging to the fullerene is not particularly favorable for strong association. Reference compound (AE)-22 (Scheme 4), in which the DB18C6 moiety is attached to the C 70 sphere by a single bridge only and, therefore, possesses higher conformational flexibility, binds K and Na ions better by factors of 2 and 20, respectively. Electrochemical studies demonstrate that cation complexation at the crown ether site causes significant anodic shifts of the first reduction potential of the appended fullerene (Table 3). In case of the C 70 mono-crown ether conjugates featuring a five o×clock functionalization pattern, addition of 1 equiv. of KPF 6 caused an anodic shift of the first reduction wave in the cyclic voltammogram (CV) by 70 to 80 mV, which is the result of the electrostatic effect of the K ion bound closely to the fullerene core (Fig. 14). Addition of 2 equiv. of K ions to C 70 bis-crown ether conjugates resulted in the observation of only one redox couple, whose potential is anodically shifted by 170 mV with respect to the corresponding wave in the absence of the salt (Fig. 16). The synthesis and characterization of novel tris-and tetrakis-adducts of ...

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confidence: 99%

Supramolecular Fullerene Chemistry: A Comprehensive Study of Cyclophane-Type Mono- and Bis-Crown Ether Conjugates of C70

Eis

Seiler

Muslinkina

et al. 2002

HCA

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“…The chirality of the [70]fullerene-crown ether conjugates is associated with an inherently chiral fullerene addition pattern in combination with the planar chiral unit of the anti-disubstituted crown ether. Interestingly, the addition pattern of (±)-16a and (±)-16b differs from that of the major product of two independent additions of untethered diethyl malonate units to C 70 [39]. A sizeable template effect was noted when the synthesis of (±)-16a and (±)-16b was carried out in the presence of KPF 6 : whereas the regioselectivity remained unaffected, the diastereoselectivity increased and the total yield went up from 41% to 68%.…”

Section: Crown Ether Tethersmentioning

confidence: 99%

Tether-directed remote functionalization of fullerenes C60 and C70

Thilgen

Diederich

2006

Comptes Rendus. Chimie

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“…In some cases, for example, upon nucleophilic cyclopropanations they even represent the exclusively formed monoadducts [1- 3,17]. Typical examples of addition reactions that afford monoadducts are epoxidations [18,19], osmylation [9], transition metal complex formations [20,21], hydrogenation [13,22], many cycloadditions [1, 2] and additions of nucleophiles [23].…”

Section: Monoadductsmentioning

confidence: 99%

“…Systematic investigations of twofold additions of malonates to C 70 revealed that the second addition takes place at one of the five α-bonds of the unfunctionalized pole [17,26]. With achiral, C 2v -symmerical malonate addends, three constitutionally isomeric bisadducts are formed: An achiral one (C 2v -symmetrical 1), and two chiral ones (C 2 -symmetrical 2 and 3), which are obtained as pairs of enantiomers with an inherently chiral addition pattern (Figure 13.5).…”

Section: Multiple Adductsmentioning

confidence: 99%