Visible-Light-Mediated Synthesis of 4H-benzo[1,4]thiazin-2-amines and 3,4-Dihydroquinoxalin-2-amines: An Efficient and Metal Free Route to C–S, C–N Bond Formation

Recent Developments on Catalyst‐Free, Visible‐Light‐Triggered Synthesis of Heterocyclic Scaffolds and Their Mechanistic Study

“…[45] Yadav et al reported an eco-friendly approach for the synthesis of benzothiazine derivatives (33) using o-amino thiophenol (30), aldehydes (31) and isocyanide (32) via CÀ S and CÀ N bond formation in aqueous ethanol under visible light irradiation at room temperature under metal free conditions (Scheme 17). [46] Easy workup procedure, operational simplicity, short reaction times, high atom economy, eco-friendly conditions and excellent yields are the noteworthy features of the protocol. EtOH : water (1 : 1) which is a polar solvent, was found to be the most appropriate solvent for this transformation during the screening of different solvents (THF, DCM, MeOH, EtOH).…”

“…Similarly, Jaiswal et al reported a resourceful methodology for the synthesis of 4-substituted 2-amino-4H-chromenes (50) using ethyl acetoacetate (46), hydrazine hydrate (47), salicylaldehyde (48) and malononitrile (49) promoted by visible light without using any catalyst (Scheme 25). [50] This one-pot multicomponent eco-friendly route gives high to excellent yield of products under solvent-free condition.…”

“…Only a trace amount of product was obtained when the reaction was carried out in the dark even after 120 mins, thus signifying the critical role of light. The authors proposed that ethyl acetoacetate (46) and hydrazine hydrate (47) underwent nucleophilic addition reaction followed by elimination reaction resulting in the formation of 26 A. Then, in the presence of visible light, malononitrile (49) underwent tautomerism to form 26 B, which then combined with salicylaldehyde (48) to form hydroxyl benzylidene malononitrile 26 C which upon cyclization afforded 2-imino-2H-chromene-3carbonitrile 26 D. Then, in presence of visible light, 26 D combined with 26 A to give 26 E, which underwent a 1,3 shift followed by enolization to give the desired product 50 (Scheme 26).…”

Derivatives of benzo-1,4-thiazine-3-carboxylic acid and the corresponding amino acid conjugates

“…Cyclocondensation of 1,3-dicarbonyl compounds with substituted diaryl disulfides in water in the presence of β-cyclodextrin gave 2,3-disubstituted benzo-1,4-thiazines in 70-91% yield in 50 min [17]. A highly efficient visible-light-mediated one-pot, three-component procedure was also explored for the preparation of 3-aryl-4Hbenzo-1,4-thiazin-2-amines [18].…”

Visible light promoted formation of N─S bond by photocatalyst Eosin Y

“…32 Despite these interesting reports for synthesis of these moieties, visible light promoted methods for synthesis of 1,2,4-thiadiazoles remains a relatively unexplored area. Accordingly, in persistence of our current research attention on the incorporating the newer alternatives to access biologically vital heterocyclic moieties in an eco-friendly green method, [33][34][35] in present study, we herein devise a novel, photocatalyed, metal-free, clean and efficient synthesis of 1,2,4thiadiazoles nucleus using organic dye eosin Y as a photoredox catalyst (Scheme 1).…”