The physical factors governing the regioselectivity of the double functionalization of fullerenes have been explored by means of Density Functional Theory calculations. To this end, the second Diels-Alder cycloaddition reactions involving 1,3-butadiene and the parent C60-fullerene as well as the ion-encapsulated system Li+@C60 have been selected. In agreement with previous experimental findings on related processes, it is found that the cycloaddition reaction, involving either C60 or Li+@C60, occurs selectively at specific [6,6]-bonds. The combination of the Activation Strain Model of reactivity and the Energy Decomposition Analysis methods has been applied to gain a quantitative understanding into the markedly different reactivity of the available [6,6]-bonds leading to the observed regioselectivity in the transformation

Financial support was provided by the Spanish Ministerio de Economía y Competitividad (MINECO) and FEDER (Grants CTQ2016-78205-P and CTQ2016 81797-REDC to I. F. and CTQ2017-85341-P to M. S.), and Catalan DIUE (projects 2017SGR39, ICREA Academia 2014 prize, and XRQTC to M. S.). The FEDER grant UNGI10-4E-801 has also funded this research. Y. G.-R. acknowledges the MINECO for a FPI grant