Regiochemistry of Multiple Additions

Hirsch, A., Lamparth, I., and Grdsscr, T. (1994) Regiochemistry of multiple additions to the fullerene core Synthesis of a T -symmetric hexakisadduct of Ca with bis(ethoxycarbonyl)methylene. J. Am. Chem. Soc. 116, 9385-9386. 

Regiochemistry of Multiple Additions 10.3.3.4 Double Diels-Alder Tethers... 

The search for alternatives to the stepwise addition of new addends to a mono-, bis-, or tris-adduct of Cr,o for the preparation of highly functionalized fullerenes has been a challenge since the beginning of fullerene chemistry. Here we present the principal approaches introduced to control the regiochemistry of multiple additions to fullerenes by the use of tethered addend systems. The tethered macro-cyclization method proved to be a major breakthrough and has provided relatively facile access to otherwise strongly disfavored addition patterns. 

For the regiochemistry of multiple additions to C o a complex picture is found. Starting from an initial 1,2-adduct, there are nine discernible sites for a second addition to another (6,6)-bond as depicted in Figure 2.35. The resulting regio-isomers are termed e, e", trans-1, trans-2, trans-3, trans-4, ds-1, cis-2, and cis-3. 

The regiochemistry of multiple additions is governed not only by steric factors but also by a tendency to avoid double bonds in five-membered rings. Thus a c/s-1-arrangement is observed with small addends, while larger addends prefer e- or frons-S-positioning. 

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