Regioselectivity in Tether-Directed Remote Functionalization - The Addition of a Cyclotriveratrylene-Based Trimalonate to C60 Revisited

The Bingel addn. of a trimalonate derived from a chiral, cyclotriveratrylene (CTV)-based tripodal tether to C60 was reinvestigated. The present use of enantiomerically pure (P)- and (M)-configured CTV units in the tether allowed the isolation of a total of four enantiomerically pure C3-sym. tris-adducts of [60]fullerene (two from each CTV enantiomer). With the support of NMR and UV/Vis spectroscopy, electronic (ECD) and vibrational (VCD) CD spectroscopic anal. (comparison to ECD data of known compds. and to ECD and VCD data calcd. by TD-DFT or ZINDO methods as part of this work) allowed a definitive detn. of the following structural features for all four CTV-C60 conjugates: (i) The constitution of the fullerene addn. pattern, (ii) its abs. configuration, and (iii) the abs. configuration of the CTV moiety. It is concluded that the triple Bingel addn. proceeded with complete regioselectivity and negligible diastereoselectivity, affording only the trans-3,trans-3,trans-3 fullerene addn. pattern in both enantiomeric forms, whereas the previously reported e,e,e motif was not formed.