Oleanolic and maslinic acids were isolated from solid waste from olive oil and several derivatives were semi-synthesised using typical reaction procedures. Rearrangements of methyl oleanate by mesylation or treatment with phosphorus pentachloride were accomplished. Six rearranged products were obtained from these reactions, three of which were 3(4)-> 5-abeo compounds formed by A-ring contraction of the oleanene skeleton. Experimental ¹³C NMR chemical shifts for 21 compounds are given and a discussion of the substituent effects on their ¹³C shieldings are also included. Moreover, theoretical ¹³C NMR chemical shifts, with the GIAO method calculated at the MM+ geometries using the B3LYP/6-31G* level, showed good agreement with the experiment, allowing a correct assignment for the experimental shifts.