stereochemistry

CARLO THILGEN, ISABELLE GOSSE, AND FRANÇOIS DIEDERICH 29
O
O
O
O
O
O
O
O
OEt
O
O
O
O
OEt
OEt
O
O
O
O
OEt
i
O
O
EtO
O
O O
O
O
O
OEt
(R,R, f (R,R)-33 A)-32
[CD(–)488]-(
(out-out,cis-3, C2 )
fA)-34 (cis-3, C2 )
(S,S, f (S,S )-33 C)-32
[CD(+)488]-(
(out-out,cis-3, C2) fC )-34
(cis-3, C2) i = C 60 , DBU, I 2 , PhMe, r. t.
ii = K 2 CO 3 , EtOH/THF
O
O O O O
i
O
EtO
O
OEt
ii
O
ii
O
O
EtO
O
EtO
O
EtO
OEt
OEt
EtO
O
O
OEt
O
O
OEt
Scheme 1.4. Selective synthesis of ( f A)- and ( f C)-bis[di(ethoxycarbonyl)methano][60]fullerene
by diastereoselective tether-directed bis-cyclopropanation of C60 and subsequent transesterification
under removal of the chiral tether auxiliary.
bis-adducts having chiral elements only in the tether moiety) by Bingel
addition to C60 of optically pure bis-malonates (R,R)-33 and (S,S)-33,
respectively. 117,125 Separate transesterification of (R,R, f A)-32 and (S,S, f C)-
32 yielded the tetraethyl esters ( f A)-34 and ( f C)-34 as pure enantiomers
exhibiting strong CD bands between 250 and 750 nm with �ε values
approaching 150 M −1 cm −1 . 117,125 Comparison with spectra calculated by
the π-electron SCF-CI-DV MO method 99,100,128 allowed an assignment of
their absolute configurations as [CD(−)488]-( f A)-34 and [CD(+)488]-( f C)-
34 (Scheme 1.4). 7 Bis-adducts derived from (S,S, f C)-32, having the diol