Te(II)-Catalyzed Cross-Dehydrogenative Phenothiazination of Anilines

Abstract

Oxidative clicklike reactions are useful for the late-stage functionalization of pharmaceuticals and organic materials. Hence, novel methodologies that enable such transformations are in high demand. Herein we describe a tellurium(II)-catalyzed cross-dehydrogenative phenothiazination (CDP) of aromatic amines. A key feature of this method is a cooperative effect between the phenotellurazine catalyst and the silver salt, which serves as a chemical oxidant for the reaction. This novel catalysis concept therefore enables a considerably broader scope compared with previous chemical oxidation methods.

Effects of the Chalcogenide Identity in N‐Aryl Phenochalcogenazine Photoredox Catalysts

“…1 H NMR (400 MHz, CDCl 3 ): δ = 7.78 (t, 2H), 7.65-7.53 (m, 5H), 7.31 (td, 2H), 7.21 (td, 2H), 6.96 ppm (dd, 2H); 13 Synthesis of 4: 10-Phenyl phenotellurazine was prepared according to a literature procedure. [37] General Procedure for O-ATRP: Photocatalyst (0.00935 mmol, 1 eq) was weighed into a 20 mL scintillation vial and brought into a nitrogen filled glovebox. DMAc (1 mL), methyl methacrylate (1 mL, 9.35 mmol, 1000 eq), and diethyl-2-bromo-2-methyl malonate (17.9 μL, 0.0935, 10 eq) were added to the vial with minimal light exposure.…”

O2-Mediated Te(II)-Redox Catalysis for the Cross-Dehydrogenative Coupling of Indoles

“…We thus commenced our study by associating our recently discovered Te(II)-phenotellurazine catalyst ( Te-cat4 , 10 mol %) with some indoles and phenols under an O 2 atmosphere, initially under basic reaction conditions ( Table 1 ). 26 , 27 While our original idea was to intercept the indole’s oxidation with a phenol, we soon identified the dehydrogenative C3–C2-coupled product 2 in 73% isolated yield (entry 1). Product 2 can be formed in a dehydorgenative fashion by a number of previously known methods.…”

“…However, tellurium can also readily accommodate many different oxidation states and is relatively versatile in its redox reactivity, as demonstrated by the seminal works of Detty, Ando, McCormick, and other research groups. − , Tellurium therefore possesses key features for complex redox catalysis. On the basis of a recent serendipitous discovery that the phenotellurazine Te-cat4 could catalyze the O 2 -mediated cross-dehydrogenative coupling of phenols with phenothiazines (Scheme d), , we envisioned that this class of Te­(II)/Te­(III) redox-labile heterocycles could furnish the basis for a new generation of broadly applicable redox catalysts. In addition, the specific chalcogen-bonding ability , of tellurium might enable new classes of coupling reactions.…”

“…We thus commenced our study by associating our recently discovered Te­(II)-phenotellurazine catalyst ( Te-cat4 , 10 mol %) with some indoles and phenols under an O 2 atmosphere, initially under basic reaction conditions (Table ). , While our original idea was to intercept the indole’s oxidation with a phenol, we soon identified the dehydrogenative C3–C2-coupled product 2 in 73% isolated yield (entry 1). Product 2 can be formed in a dehydorgenative fashion by a number of previously known methods. − However, only a few utilized O 2 as the terminal oxidant, and these sometimes required a photochemical setup. − It soon transpired that both the phenol additive and the Te catalyst are essential for this reaction (Table , entries 1–3).…”

Cyclic Hypervalent Iodine-Induced Oxidative Phenol and Aniline Couplings with Phenothiazines

“…To date, synthetic routes for N -arylphenothiazines have been limited to phenol–phenothiazine couplings via radical intermediates . Aniline-phenothiazine coupling reactions have recently been reported. − Although the coupling methods proposed by Patureau (Ag 2 O or tellurium­(II)-catalyzed method , ) and Lei (K 2 S 2 O 8 -based method), the electrode oxidation studied by Li and Tan, , and Fe-catalyzed method by Knölker are well-known, the substrate scopes of phenols and anilines in these reactions are limited.…”