Palani Natarajan

Visible light-mediated intramolecular C–H arylation of diazonium salts of N-(2-aminoaryl)benzoimines: a facile synthesis of 6-arylphenanthridines

Utilizing [Ru(bpy)3]Cl2 as a photoredox catalyst and a blue LED as an irradiation source, moderate to good yields of 6-arylphenanthridines were obtained from aryl diazonium salts in situ formed from the reactions of N-(2-aminoaryl)benzoimines and tert-butyl nitrite (tBuONO). Although few visible light-mediated protocols are available for the synthesis of 6-arylphenanthridines, this work provides a new method to access them readily from inexpensive and environmentally benign starting materials.

Teaching old compounds new tricks: DDQ-Photocatalyzed C-H Amination of Arenes with Carbamates, Urea and N-Heterocycles

Abstract The C−H amination of benzene derivatives was achieved using DDQ as photocatalyst and BocNH2 as the amine source under aerobic conditions and visible light irradiation. Electron‐deficient and electron‐rich benzenes react as substrates with moderate to good product yields. The amine scope of the reaction comprises Boc‐amine, carbamates, pyrazoles, sulfonimides and urea. Preliminary mechanistic investigations indicate arene oxidation by the triplet of DDQ to radical cations with different electrophilicity and a charge transfer complex between the amine and DDQ as intermediate of the reaction.

Transition-metal-free and organic solvent-free conversion of N-substituted 2-aminobiaryls into corresponding carbazoles via intramolecular oxidative radical cyclization induced by peroxodisulfate

An atom-economical and environmentally benign approach for the synthesis of N-substituted carbazoles from analogous 2-aminobiaryls using peroxodisulfate in water is reported. The reactions proceeded through an intramolecular oxidative radical cyclization of N-substituted 2-aminobiaryls with in situ reoxidation of the resulting radical species. When compared to known methods for the synthesis of N-substituted carbazoles from 2-amidobiaryls, this protocol is practical, efficient and does not require a transition metal catalyst or toxic organic solvents.

Isomorphous three-component crystals (pseudopolymorphs of binary cocrystals) based on lattice inclusion of guests with a sterically-rigidified tetraarylpyrene host

Based on structural studies already available for the cocrystals of a sterically-rigidified tetraarylpyrene (TP) host substituted at the periphery by flexible methoxymethyl (MM) groups, i.e., TPMM, with aliphatic guests, formation of ternary or three-component cocrystals was targeted by replacing one of the guest species in the binary cocrystals with a different guest. Ternary cocrystals of TPMM with cyclododecene + cyclodecane, cyclododecene + cyclooctane and cyclododecene + decalin pairs were indeed successfully isolated and characterized by single-crystal X-ray structure determination. The ternary cocrystals, in principle, constitute ‘isomorphous pseudopolymorphs’ of binary cocrystals of TPMM with cyclododecene.

Visible light photoredox catalysis: conversion of a mixture of thiophenols and nitriles into 2-substituted benzothiazoles via consecutive C–S and C–N bond formation reactions

A novel, visible-light-mediated method for the construction of 2-substituted benzothiazoles from easily available thiophenols (2.0 equiv.) and alkyl/aryl nitriles (1.0 equiv.) in the presence of eosin Y (0.02 equiv.) under air atmosphere has been developed. The reaction proceeded smoothly, for a wide range of derivatives of thiophenols and nitriles, to give the expected products in moderate to good yields. A reaction mechanism involves the direct oxidative radical coupling of thiophenols with nitriles to afford iminyl radical intermediates giving the expected product by an intramolecular cyclization followed by hydrogen radical loss. To the best of our knowledge, this is the first example of the synthesis of 2-substituted benzothiazoles through sequential C–S and C–N bond formation reactions under photoredox catalysis.