Visible light-mediated photocatalytic oxidative cleavage of activated alkynes via hydroamination: a direct approach to oxamates.

The direct oxidative cleavage of activated alkynes via hydroamination has been described using organic photocatalyst under visible-light irradiation at room temperature. In this reaction, the single electron oxidation of an in situ formed enamine followed by radical coupling with an oxidant finally delivers the oxamate. The key features of this photocatalytic reaction are the mild reaction conditions, metal-free organic dye as a photocatalyst, and TBHP playing a dual role as "O" source and for the regeneration of the photocatalyst.

Exocyclic N-Acyliminium Ion (NAI) Cyclization: Access to Fully Substituted Oxazoles and Furocoumarins.

A concise, one-pot route to oxazoles and furocoumarins has been reported. The key step in this transformation involves in situ generation of N-acyliminium ion (NAI) precursor under catalyst and solvent-free conditions and their further transformations promoted by superacid in the same pot. We have also presented the experimental evidence for the involvement of proto-solvated novel exocyclic N-acyliminium ion. Further, the UV-visible and fluorescence studies revealed that few of the compounds reported here exhibited emission of blue light upon irradiation in EtOH in the region of 404-422 nm.

Regioselective C3-H Trifluoromethylation of 2 H-Indazole under Transition-Metal-Free Photoredox Catalysis.

Trifluoromethyl-substituted heteroarenes are biologically active compounds and useful building blocks. In this sequence, we have developed a visible-light-promoted regioselective C3-H trifluoromethylation of 2 H-indazole under metal-free conditions, which proceeds via a radical mechanism. The combination of photocatalysis and hypervalent iodine reagent provides a practical approach to a library of trifluoromethylated indazoles in 35-83% yields.

Iron promoted C3-H nitration of 2H-indazole: direct access to 3-nitro-2H-indazoles.

An efficient C3-H functionalization of indazole has been demonstrated. Notably, this method involves chelation-free radical C-H nitration on 2H-indazole. The radical mechanism was confirmed by control experiments and quantum chemical calculations. The synthetic utility has been proven by the synthesis of bio-relevant benzimidazoindazoles via reductive cyclization.

C(sp(2))-H Functionalization of 2H-Indazoles at C3-Position via Palladium(II)-Catalyzed Isocyanide Insertion Strategy Leading to Diverse Heterocycles.

Herein, we have reported an efficient Pd-catalyzed C-H functionalization of 2H-indazole at C3-position via an isocyanide insertion strategy for the synthesis of unprecedented benzoxazinoindazoles, indazoloquinaoxalines and benzoxazinoindazolones for the first time. Our new method provides an operationally simple and versatile route for a selective synthesis of 2-(2H-indazol-2-yl)phenols. Furthermore, we developed a sequential one-pot strategy for the synthesis of benzoxazinoindazolone under metal-oxidant-free conditions. We also achieved the isocyanide insertion between C(sp(2))-H and oxygen heteroatom for the first time. The key features of the present protocol are construction of 4 bonds in one-pot, synthesis of new skeletally diverse scaffolds, broad substrate scope, high yields and environmentally benign conditions.