Synthesis of Purines and Related Molecules by Cyclization -Reactions of Heterocyclic Enamines

A great variety of pharmacologically relevant fluorinated purine analogues are available by cyclization reactions of heterocyclic enamines with 1,3-dielectrophiles. The reactions usually proceed with excellent regioselectivities. As electrophiles, 1,3-diketones, enaminones or 3-chloro-2-en-1-ones were used. Other synthetic strategies are based on inverse-electron-demand Diels-Alder reactions of heterocyclic enamines with triazines. Purine analogues were further functionalized by transition-metal-catalyzed CH-coupling reactions or oxidative cyclizations, giving rise to more complex polycyclic products. Amidino- C -glycosides in their reactions with 1,3-dielectrophiles afforded pyrimidine- C -glycosides. Multicomponent reactions of heterocyclic enamines afforded complex products, including spirocyclic derivatives.