Preparation of dendrobine intermediate ethyl cyclopentenyl ester using RCM strategy

Ethyl 2-methylcyclopent-2-ene-1-carboxylate ( 3 ) is an important building block in the synthesis of some natural products. In this paper, 2 GGC was used for the RCM reaction to prepare this scaffold instead of reported 1 GGC. This scaffold ( 3 ) was obtained in a moderate yield and its structure was determined by 1 H NMR and 13 C NMR. A contra-ring closing metathesis mechanism was also put forward to explain the formation of the product. Graphical abstract