Visible Light-Driven and Singlet Oxygen-Mediated Photochemical Cross-Dehydrogenative C₃–H Sulfenylation of 4-Hydroxycoumarins with Thiols Using Rose Bengal as a Photosensitizer

Abstract

A visible light (white light-emitting diode/direct sunlight)-driven photochemical synthesis of a new series of biologically interesting 3-(alkyl/benzylthio)-4-hydroxy-2H-chromen-2-ones has been achieved through a cross-dehydrogenative C3–H sulfenylation of 4-hydroxycoumarins with thiols at ambient temperature in the presence of rose bengal in acetonitrile under an oxygen atmosphere. The notable features of this newly developed method are mild reaction conditions, energy efficiency, metal-free synthesis, good to excellent yields, use of low-cost materials, and eco-friendliness.

Nonyl Acridine Orange as a Prospective Photocatalyst in Chalcogenylation of Coumarins and Quinolinones

“…During preparation of this manuscript, a method for synthesis of 4-hydroxy-3-sulfenylcoumarins in the presence of Rose Bengal under visible light irradiation was demonstrated. 17 Obviously, more conventional ways exist for preparation of 3-sulfenyl coumarins that do not rely on the use of light irradiation. A regioselective method for sulfenylation of 4anilinocoumarins was performed utilizing Bunte salts and KI as a catalyst, 18 whereas sulfenylation of 4-hydroxycoumarin with Bunte salt was achieved using H 2 O 2 and HBr.…”

“…Then, dicyanodiselenide may be attacked by 1a • or 1b • radicals (Scheme 5, pathway B). 17 The comparison of photoluminescence quenching constants of NAO with 1a, 1b, 2l, and 4c allowed us to conclude that all tested compounds may form a radical; however, quenching constants for hydroxycoumarin 1a (1.8 × 10 −3 L/mol) and thiocyanate 2l (1.5 × 10 −3 L/mol) were higher than for selenocyanate 4c (0.4 × 10 −3 L/mol) and significantly higher than for 1b (0.1 × 10 −3 L/mol). Thus, pathway A is preferable for 4-aminocoumarin 1b, pathway B for 4-hydroxycoumarin 1a.…”

Metal-free photo-induced sulfidation of aryl iodide and other chalcogenation

“…In the past few years, the photoredox transition metal-catalyzed C-S cross-coupling between aryl halides and thiols/disulfides have been widely developed, in which a series of Cu, Ni, Pd, and Rh transition metals are still utilized as catalysts (Figure 2C). (Uyeda et al, 2013;Wang et al, 2013;Johnson et al, 2016;Jouffroy et al, 2016;Jouffroy et al, 2016;Oderinde et al, 2016;Li et al, 2020;Sandfort et al, 2020;Brahmachari et al, 2021;Qin et al, 2021;Yang et al, 2021) Meanwhile, A series of photo-induced transition-metal and photosensitizer free C−S cross-coupling methods has been developed (Bunnett and Creary, 1974;Liu et al, 2017;Pramanik et al, 2020;Dawei Cao et al, 2021;Nandy et al, 2021;Saroha et al, 2021;Shun Wang et al, 2021;Uchikura et al, 2021;Wang et al, 2022). For the metal-free synthesis of aryl sulfides, Hong and co-workers developed a convergent, organocatalytic visible-light-mediated process for the synthesis of diaryl sulfides (Hong et al, 2017).…”

“…In the past few years, the photoredox transition metal-catalyzed C–S cross-coupling between aryl halides and thiols/disulfides have been widely developed, in which a series of Cu, Ni, Pd, and Rh transition metals are still utilized as catalysts ( Figure 2C ). ( Uyeda et al, 2013 ; Wang et al, 2013 ; Johnson et al, 2016 ; Jouffroy et al, 2016 ; Jouffroy et al, 2016 ; Oderinde et al, 2016 ; Li et al, 2020 ; Sandfort et al, 2020 ; Brahmachari et al, 2021 ; Qin et al, 2021 ; Yang et al, 2021 )…”

Catalyst- and Additive-Free C(sp3)–H Functionalization of (Thio)barbituric AcidsviaC-5 Dehydrogenative Aza-Coupling Under Ambient Conditions

“…As part of our ongoing endeavors in green chemistry-directed C–H functionalizations of useful organic scaffolds, we thus felt pertinent in designing an efficient and practical C­(sp 3 )–H functionalization protocol to synthesize a series of diversely substituted barbituric/2-thiobarbituric hydrazones via C-5 dehydrogenative aza-coupling . Substituted pyrimidines, categorically barbituric/2-thiobarbituric acids, act as building blocks for a handful of useful drugs with hypnotic, sedative, anticonvulsant, anaesthetic, antioxidant, antifungal, and central nervous system depressant activity .…”