Addition patterns, chiral cycloaddition reactions

Systematic investigations of twofold additions of malonates to C70 revealed that the second addition takes place at one of the five a-bonds of the unfunctionalized pole [17, 26], With achiral, C2v-symmerical malonate addends, three constitutionally isomeric bisadducts are formed An achiral one (C2v-symmetrical 1), and two chiral ones (C2-symmetrical 2 and 3), which are obtained as pairs of enantiomers with an inherently chiral addition pattern (Figure 13.5). Twofold addition of chiral malonates leads to the formation of five optically active isomers, two constitutionally isomeric pairs of C2-symmetrical diastereomers and a third constitutional C2-symmetrical isomer (Figure 13.5). Twofold additions of azides to C70 lead to diazabis[70]homo-fullerenes, which served as starting material for the synthesis of bis-(aza[70]-fullerenyl) (Cg9N)2 (Chapter 12) [27]. As further bisadditions, addition reaction to C70 [2+2]cycloaddition of electron-rich bis(diethylamino)ethyne and 1-alkylthio-2-(diethylamino)ethynes [28] and the addition of transition metal fragments have been reported [29-32],... 

A complex, multiply bridged 1,2,3,4-adduct of C60 (168) (Scheme 1.11) including a noninherently chiral addition pattern as well as a multitude of stereogenic centers in the addend moiety was obtained in a tandem reaction between the alkaloid scandine and Ceo-324 The sequence included a photoin-duced addition of the tertiary amine subunit of the alkaloid and a [2 + 2] cycloaddition of its vinyl group to the adjacent intrahexagonal formal double bond of the fullerene. The structural elucidation included 1H-1 H COSY-, HMQC- (heteronuclear multiple quantum coherence), HMBC-, and ROESY-(rotating frame Overhauser enhancement spectroscopy) NMR experiments and... 

The isoquinuclidine ring system is readily accessible through various synthetic routes. The most widely used approach to the construction of the ISQ ring system is through Diels-Alder or 4+2 cycloaddition reactions. Dihydropyridines (DHPs) or 1,3-cyclohexadienes are most commonly employed as diene components and various dienophiles have been employed based on the substitution pattern of the final desired product. Intramolecular cyclizations, tandem-Michael addition/aldolizations or cyclization via tricyclic aziridines or perhydro / -aminobenzoic acid derivatives have also been reported. Several synthetic routes employing asymmetric or chiral synthetic approaches have also been reported. Most recently, solution-phase parallel synthesis of ISQ derivatives using several of these approaches has been reported [49,50,51]. 

Scheme 1.11. Diastereoselective synthesis of a Cgo-scandine conjugate by tandem reaction sequence involving a photoinduced addition of a tertiary amine and a [2 + 2] cycloaddition. The structure of the product includes a noninherently chiral functionalization pattern in addition to stereogenic centers in the alkaloid moiety.

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