Synthesis of Tricyclic Methyl Cyclopentapyridopyrimidin‐6‐carboxylates and Cyclopentaimidazopyridin‐6‐carboxylates from Genipin

An effective one-pot reaction was successfully developed for the synthesis of tricyclic methyl cyclopentapyridopyrimidin-6-carboxylates and cyclopentaimidazopyridin-6-carboxylates from genipin with a variety of diamines, including aliphatic, sterically hindered substituted and N-substituted diamines, and cyclohexane-1,2-diamine under nitrogen atmosphere. The tricyclic and tetracyclic methyl cyclopentapyridopyrimidin-6-carboxylate or cyclopentaimidazopyridin-6-carboxylate were successfully afforded in good to excellent yields. This facile and efficient one-pot reaction involved N-substitution reaction, cyclization, sequential dehydration, and final N-substitution reaction in four-step reactions. The reactivity tendency of diamines was also determined from the isolated yields of products in this work. On the other hands, we also evaluated genipin with amines and diamines under air atmosphere to determine the potential colour variation range areas. Fortunately, we firstly isolated the unstable methyl dihydro-2H-cyclopenta[c]pyridine-4-carboxylate intermediates 3 a-b and assigned by simple spectrum analysis technique.