Semi-synthesis of triterpene A-ring derivatives from oleanolic and maslinic acids. Part II. Theoretical and experimental C-13 chemical shifts

Maslinic acid was obtained from olive-pressing residues, and several deriva tives were formed. Rearrangements of 2-tosyloxy-derivatives of methyl masli nate made out by acetolysis. The main product of these rearrangements conta ined a cyclopentanic A-ring as a result of a concerted 2(3) --> 4-abeo rear rangement process. Experimental and theoretical (GIAO, B3LVP/G-31G*//MM+) C -13 NMR chemical shifts for 20 compounds are given.