Synthesis, separation and characterisation of the first pure multiple adducts of C2v- and D3-C78

Abstract

Multiple cyclopropanation of an isomeric mixture of C_2v- and D₃-C₇₈ (ca. 3∶1) with diethyl 2-bromomalonate yielded two C₁-symmetrical bis-adducts, one of which was isolated without HPLC, and at least eight isomeric tris-adducts. Most of the adducts were isolated in pure state by HPLC and characterised by UV–VIS, ¹H and ¹³C NMR spectroscopy, as well as by mass spectrometry. In the case of the tris-adducts, three isomers displayed a higher symmetry than C₁ and could therefore be unambiguously assigned to the C₇₈ isomer from which they arise. Three possible structures were finally proposed for a C₂-symmetrical tris-adduct of C_2v-C₇₈, and two structures for a C₃-symmetrical tris-adduct of D₃-C₇₈. Based on the comparison of the spectra obtained for the C₂-symmetrical tris-adduct with those of the bis-adducts, three possible structures were proposed for one of the C₁-symmetrical bis-adducts, being the direct precursor of the corresponding tris-adduct. The compounds described in this work represent the first adducts of C_2v- and D₃-C₇₈ isolated and characterised in a pure state.