9-Substituted 2-chloro-6-sulfonylpurines provide 6azido-2-sulfonylpurine derivatives with 61−83% yields when treated with sodium azide. Under optimized reaction conditions, the title compounds are obtained in a one-pot process, which involves a sequential treatment of 2,6-dichloropurines with a selected sodium sulfinate and sodium azide. Such a sulfonyl group dance (functional group swap) results from a cascade of S N Ar reactions, which are facilitated by azidoazomethine-tetrazole (azide-tetrazole) tautomeric equilibrium. The formation of Meisenheimer-type intermediates as tetrazolopurine tautomers was supported by various spectroscopic methods, including 15 N NMR.
Purines, which are regarded as relatively stable heterocyclic systems, can be opened at both pyrimidine and imidazole rings. Purine ring opening also serves as a tool for the preparation of ring-modified purines through rearrangement/recyclization mechanisms. The obtained imidazole, pyrimidine, and purine derivatives are privileged molecular scaffolds in medicinal and agricultural chemistry. Purine ring-opening approach is a useful alternative for their synthesis, which competes well with de novo approach or modification of a conserved heterocyclic core. The substitution patterns and groups that activate purines towards ring opening are reviewed. Moreover, mechanistic studies using labelled substrates, which are leading to rearranged purine derivatives are covered. Furthermore, an insight into imidazole ring opening upon exposure of purine system to DNA damaging agents is provided.
The Cover Feature shows the essence of purine ring opening pathways. Electrophilic activation of purine by pulling its electron density from N(1) or N(7) and subsequent nucleophile attack ensures the ring‐opening of the pyrimidine or imidazole part of the parent heterocycle. The obtained products can be used as such or submitted to further rearrangements and cyclizations. This methodology is a useful addition to the synthetic toolbox of heterocyclic chemistry. More information can be found in the Review by I. Novosjolova, M. Turks et al.
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