stereochemistry

CARLO THILGEN, ISABELLE GOSSE, AND FRANÇOIS DIEDERICH 21
of the CD spectra of C60-bis-adducts with an inherently chiral addition pattern
(Figure 1.13; the obtained compounds with unassigned absolute configurations
are represented as racemates (±)-5 and (±)-6) or, in other words, of inherently
chiral C60-derived π-chromophores. 106
b. Methanofullerene Derivatives Resulting from Functionalization
with Independent (Nontethered) Addends. Bingel type adducts, namely
bis(alkoxycarbonyl)methanofullerene derivatives resulting from addition of
2-halomalonate anions across a 6–6 bond of a fullerene, 94,107 are probably
the most extensively studied class of fullerene derivatives. They have thus
provided the largest body of knowledge on the regio- and stereochemistry of
multiple additions to C60 and the higher fullerenes. 14–17,22,28,42,108 In a twofold,
stepwise addition of diethyl-2-bromomalonate, Hirsch and co-workers were
able to isolate seven of the eight possible bis-adducts (cf. Figure 1.12b), and
they assigned their structures based on a combination of NMR spectroscopy
and the HPLC elution order which is related to their polarity. 51 Among the
isolated tetraesters, three ((±)-7 (cis-3), (±)-8 (trans-3), and (±)-9 (trans-2))
had an inherently chiral addition pattern (Figure 1.13).
X =
O
OsO2(Py) 2
O
C(CO 2Et) 2
NCO 2Et
Ph
O
N
N
Ph
O
X
cis-3
(C 2)
(±)-7
X
X
trans-3
(C 2)
(±)-5
X
X
trans-2
(C 2)
(±)-6
(±)-8 (±)-9
(±)-56 (±)-57 (±)-58
(R,R,R,R, f C)-13/
(R,R,R,R, f A)-14
X
(R,R,R,R, f C)-15/
(R,R,R,R, f A)-16
Figure 1.13. Bis-adducts of C60 with an inherently chiral addition pattern. Each regioisomer is
represented by a single, f C-configured structure. The configuration of actually obtained products
is indicated in each case by a descriptor preceding the compound number.