Chiral functionalization pattern

II. CONFIGURATIONAL DESCRIPTION OF CHIRAL FULLERENES AND FULLERENE DERIVATIVES WITH A CHIRAL FUNCTIONALIZATION PATTERN... 

Derivatives of achiral parent fullerenes in which the functionalization creates a chiral addition pattern on the spheroid, regardless of the addends being identical or different, have an inherently chiral functionalization pattern. The derivatives of chiral parent fullerenes automatically have an inherently chiral functionalization pattern. 

Derivatives of achiral parent fullerenes in which the chirality of the functionalization pattern is due only to nonidentities among addends, have a noninherently chiral functionalization pattern. The analogy of this situation to that of a center of chirality should be noted. 

Derivatives of Achiral Parent Fullerenes with an Inherently Chiral Functionalization Pattern... 

As the parent fullerene is achiral, its C-atom numbering can in principle be achieved with either one of the two mirror-symmetric numbering schemes. For a particular enantiomer of its derivatives with an inherently chiral functionalization pattern, however, a single numbering scheme only leads to the lowest set of locants for the addends (cf. Sections IV.A.l and IV.A.2) (Figure 1.4). 

As to the chirality of the observed fluoro- and hydrofullerenes, it is evident that those derived from chiral parent fullerenes, such as C76, have an inherently chiral functionalization pattern. In the other cases no further information is currently available. 

Osmates with an inherently chiral functionalization pattern have been synthesized by Hawkins and co-workers as intermediates in the kinetic resolution of D2-C76,4 5 >3-C78, and D2-C84 (cf. Section III.C).5... 

Figure 135. C -symmetric 1,4-adducts of (V,o with a noninherently chiral functionalization pattern. The general structural formula is depicted in two different views of which the right one illustrates well that there is no mirror plane including the two added residues.

Figure 1.36. Dimeric 1,4-adducts of Cgo with a noninherently chiral functionalization pattern in each spheroid. Whereas the combination of homochiral moieties leads to a d, l pair of enantiomers, that of heterochiral cages gives rise to a meso form.

Figure 1.38. Multiply bridged dimeric derivatives of C60 with noninherently chiral functionalization patterns in spheroids of the 1,2,3,4-adduct type.

Figure 1.39. Two different noninherently chiral functionalization patterns realized in a 1,2,3,4-(( >-167) and a 1,2,3,6-adduct (( >-172) of C60.

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.

Scheme 1.12. A tandem sequence of Michael-type addition and [4 + 2] cycloaddition diastere-oselectively affords highly functionalized 1,2,3,4-derivatives of Cgo (type ( )-169) with two adjacent bridges and a noninherently chiral functionalization pattern. Deprotonation of ( )-169 and subsequent alkylation leads to an inherently chiral addition pattern in ( )-170.

Figure 1.41. The Jt3-ri2 r 2 r 2-ligation of Cco to the carbido-pentaruthenium cluster of ( )-180 results in a noninherently chiral functionalization pattern of the cts-l,ci.v-1, d.v-l type.

Figure 1.43. C(5)-C(6)-adducts (( )-184 and ( )-187), and a decakis-adduct (( )-191) of C70 with noninherently chiral functionalization patterns, together with other congeners formed in the respective syntheses.

The configuration of Cgo and C70 derivatives with a chiral functionalization pattern can easily be computed via the interactive Website www.diederich.chem.ethz.ch/chirafull. 

Since cis-3, trans-3, and trans-2 bis-adducts of 50 with identical addends are chiral as a result of inherently chiral functionalization patterns [10, 44-46], it was of interest to explore whether Bingel macrocyclizations with bismalonates bridged by non-racemic tethers would provide an enantioselective synthesis of these compounds. An overall enantioselective synthesis of optically active Cgg bis-adducts had been achieved previously by asymmetric Sharpless bis-osmylation [77] however, this sequential bis-func-tionalization lacks the regioselectivity of the Bingel macrocyclization, and therefore requires tedious regioisomer separations. 

Of substantial interest were the chiroptical properties of these enantiomeric 60 derivatives with chiral functionalization patterns the mirror-image CD spectra of ( C)-2 and ( A)-2 displayed large Cotton effects between 250 and 750 nm with Ae values approaching 150 cm mmoL [25, 59]. These intensities of the CD bands are of similar magnitude to those measured for inherently chiral fullerenes (such as D2-C76 [78] and their derivatives [79]) but are much larger than those measured for non-racemic fullerene derivatives in which the chirality only results from the addends [25]. 

The e bis-adducts 45 (Scheme 7-8) and ent-AS (not shown) provide examples for optically active fullerene derivatives in which the chirality originates only from the optically active tether, and the intensities of their CD bands (Ae values < 30 cm mmol" ) are smaller than those of ( C)-2 and i A)-2 (Scheme 7-11) with inherently chiral functionalization patterns [25]. 

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