Iodine-catalyzed oxidative functionalization of purines with (thio)ethers or methylarenes for the synthesis of purin-8-one analogues

Iodine-Catalyzed Cascade Annulation of 4-Hydroxycoumarins with Aurones: Access to Spirocyclic Benzofuran-Furocoumarins

An attractive approach for the preparation of spirocyclic benzofuran-furocoumarins has been developed through iodine-catalyzed cascade annulation of 4-hydroxycoumarins with aurones. The reaction involves Michael addition, iodination, and intramolecular nucleophilic substitution in a one-step process, and offers an efficient method for easy access to a series of valuable spirocyclic benzofuran-furocoumarins in good yields (up to 99%) with excellent stereoselectivity. Moreover, this unprecedented protocol provides several advantages, including readily available materials, an environmentally benign catalyst, a broad substrate scope, and a simple procedure.

Iodine-Catalyzed Radical C-H Amination of Nonaromatic Imidazole Oxides: Access to Cyclic α-Aminonitrones

A straightforward cross-dehydrogenative coupling approach to incorporate alicyclic amino residues into the structure of model cyclic aldonitrones, 2H-imidazole oxides, is reported. The elaborated C(sp2)-H functionalization is achieved by employing cyclic amines in the presence of the I2-tert-butyl hydroperoxide (TBHP) reagent system. As a result, a series of 19 novel heterocyclic derivatives were obtained in yields of up to 97%. A mechanistic study involving electron paramagnetic resonance spectroscopic experiments allowed the radical nature of the reaction to be confirmed. In particular, the envisioned mechanistic rationale comprises N-iodination of a cyclic amine, followed by N-I bond homolysis of the resulting intermediate and subsequent amination of the nitrone moiety via the newly generated nitrogen-centered radical.

Selectfluor-Induced Oxidative Amination of N-Heteroaromatics with Purine

An oxidative coupling reaction between purines and aromatic N-heterocycles was developed to synthesize a series of N-heteroaryl purine derivatives using Selectfluor as an oxidant at room temperature. This process uses a commercial oxidant, uses no base, metal, or other additives, is simple to carry out, and has a broad range of substrates.

Visible light-induced direct alkylation of the purine C8-H bond with ethers

The one-step visible light-induced direct alkylation of the C₈-H bond for purine derivatives by ethers was developed using Eosin Y as the photocatalyst and t-BuOOH as the oxidant at room temperature. This method describes the coupling of the α-C of the ether to the C₈ of purine. Of particular interest is that substrates include purines with various functional groups and even unprotected 9H-purines. The protocol provides an effective method for the synthesis of 8-alkylpurine derivatives with high atom economy and high regioselectivity.