Mechanistic Study of a Photocatalyzed CS Bond Formation Involving Alkyl/Aryl Thiosulfate

Abstract

This study presents thioether construction involving alkyl/aryl thiosulfates and diazonium salt catalyzed by visible-light-excited [Ru(bpy)3 Cl2 ] at room temperature in 44-86 % yield. Electron paramagnetic resonance studies found that thiosulfate radical formation was promoted by K2 CO3 . Conversely, radicals generated from BnSH or BnSSBn (Bn=benzyl) were clearly suppressed, demonstrating the special property of thiosulfate in this system. Transient absorption spectra confirmed the electron-transfer process between [Ru(bpy)3 Cl2 ] and 4-MeO-phenyl diazonium salt, which occurred with a rate constant of 1.69×10(9) M(-1) s(-1) . The corresponding radical trapping product was confirmed by X-ray diffraction. The full reaction mechanism was determined together with emission quenching data. Furthermore, this system efficiently avoided the over-oxidation of sulfide caused by H2 O in the photoexcited system containing Ru(2+) . Both aryl and heteroaryl diazonium salts with various electronic properties were investigated for synthetic compatibility. Both alkyl- and aryl-substituted thiosulfates could be used as substrates. Notably, pharmaceutical derivatives afforded late-stage sulfuration smoothly under mild conditions.

A Visible‐Light‐Driven, Metal‐free Route to Aromatic Amides via Radical Arylation of Isonitriles

“…Synthesis of arylazo sulfones 1 a – s . Diazonium salts were prepared just before use from the corresponding anilines and purified by dissolving in acetone and precipitation by adding cold diethyl ether. To a cooled (0 °C) suspension of the appropriate diazonium salt (1 equiv, 0.3 M) in CH 2 Cl 2 was added sodium methanesulfinate (1 equiv.…”

Synthesis of aryl sulfides via radical–radical cross coupling of electron-rich arenes using visible light photoredox catalysis

“…Three of the five most selling drugs in 2015 were organosulfur compounds. The majority of methods for C–S bond synthesis use transition metal-catalyzed cross coupling of thiols and their derivatives with organohalides [ 4 – 6 ], arylboronic acids [ 7 ], aryl triflates [ 8 ], and diazonium salts [ 9 ]. Typical metals used are palladium [ 10 – 13 ], copper [ 14 – 21 ], nickel [ 22 – 24 ], iron [ 25 – 29 ], cobalt [ 30 – 32 ], and rhodium [ 33 – 34 ].…”

Visible Light-Promoted Formation of C–B and C–S Bonds under Metal- and Photocatalyst-Free Conditions

“…Organic solvents were purified from by solvent purification system MBraun SPS-5 and stored over molecular sieves under argon. Diazonium salts were synthesised by following a known procedure 16 and purified by recrystallisation from acetone/Et 2 O. For irradiation of the reaction mixtures, different light sources were used: a) blue LED stripes (12W, 24 W) and b) H150 Kessil lamp (34 W, λ = 420 nm).…”