SYNTHETIC AND COMPUTATIONAL STUDIES ON SYMMETRY-DEFINED DOUBLE CYCLOADDITION OF A NEW TRIS-ANNULATING REAGENT TO C-60

For the purpose of doubly functionalizing fullerenes, new tris-annulat ing reagents 2(n) have been developed. The reagents carry, in one mole cule, two cyclopropenone acetals which are connected with an n-carbon methylene tether. Upon thermolysis of 2(n) in the presence of C-60, th e reagent undergoes [3 + 2] cycloaddition reaction twice in a regio- a nd stereoselective manner to give C-s and C-2 organofullerenes bearing two cyclopentenone acetals. The selectivity varies as the function of the tether structure. The experiments have shown that, in each series of different tether lengths, one can obtain one or two diastereomeric double adducts out of several structural possibilities. The selectivi ty of the reaction did not conform to the prediction made on the basis of previous knowledge on intermolecular double additions but was foun d to be correlated to the conformational strain of the tether moiety, which can be estimated by a newly developed ''double differential prot ocol''. Systematic studies on the reliability of various computational methods for organofullerenes indicated that certain molecular orbital and molecular mechanics calculations give very reliable structural da ta while certain others do not.