Cascade bicyclization of triethylammonium thiolates with hydrazines: efficient access to pyrazolo[3,4-c]quinolines

Abstract

A new bicyclization strategy has been established, allowing a flexible and practical approach to 33 examples of pyrazolo[3,4-c]quinolines from low-cost and readily accessible triethylammonium thiolates with hydrazines. Notably features of this work include broad functional group compatibility, mild reaction conditions and good reaction yields.

I2-Catalyzed sulfenylation of indoles and pyrroles using triethylammonium thiolates as sulfenylating agents

“…Triethylammonium thiolate 1a was treated with 2-phenyl-1 H -indole 2a in the presence of 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) or butylhydroxytoluene (BHT) (2.0 equiv) under the standard conditions, and the corresponding product 4a was afforded in 86% yield, confirming that the transformation did not involve a radical process, different from our previous report (Scheme 5a). 17b The reaction under Ar conditions gave the product 4a in 85% yield, indicating that DMSO could serve as both an oxidant and a reaction solvent (Scheme 5b). Furthermore, triethylammonium thiolate 1a was carried out under the standard conditions without indole 2a , furnishing disulfane 8a in 93% yield (Scheme 5c).…”

“…17 For instance, we presented I 2 /O 2 -enabled [3 + 2] cyclization of the preformed triethylammonium thiolates with arylhydrazines, allowing the direct radical N-S bond coupling to provide functionalized 1,2,3-thiadiazoles (Scheme 1a). 17b During this project, we believed that under suitable catalytic conditions, triethylammonium thiolates could serve as an eco-friendly sulfenylating agent for the synthesis of 3-sulfenylindoles through regioselective sulfenylation of indoles as it behaves stable nature, accessibility and high reactivity under air conditions.…”

“…17 For instance, we presented I 2 /O 2 -enabled [3 + 2] cyclization of the preformed triethylammonium thiolates with arylhydrazines, allowing the direct radical N-S bond coupling to provide functionalized 1,2,3-thiadiazoles (Scheme 1a). 17b During this project, we believed that under suitable catalytic conditions, triethylammonium thiolates could serve as an eco-friendly sulfenylating agent for the synthesis of 3-sulfenylindoles through regioselective sulfenylation of indoles as it behaves stable nature, accessibility and high reactivity under air conditions. Herein, we would like to report the successful realization of this idea with I 2 -catalyzed intermolecular C(sp2)-S bond coupling for the flexible synthesis of unprecedented C,S -tethered bisindoles 4 using triethylammonium thiolates 1 as a significant and reliable sulfenylating agent via C3 sulfenylation of indoles 2 (Scheme 1b).…”

Iodine and DMSO as Surrogate of Hazardous Metal and Non‐Metal Reagents in Organic Synthesis

“…Fan and coworkers have investigated the roles of triethylammonium thiolates as an efficient sulphur reagent. [88][89][90][91] Recently in 2023, Fan's research group [92] came up with the idea of synthesis of pyrazole thioethers through the functionalization of hetetrocyles like pyrazoles, isoxazoles and isothiazoles using sulphur reagents (Scheme 8 (g)). The catalytic amounts of iodine has participated in this transformation in the presence of DMSO at 100 °C temperature under microwave irradiation to accomplish the complete conversion in 30 minutes of reaction time.…”

Ultrasonic Methylation of Triethylammonium Thiolate as a Key Strategy for Synthesis of Tetrahydropyrazine‐Containing 2‐Oxindole Scaffold

“…Recently, triethylammonium thiolates have attracted the attention of organic chemists for preparation of biologically active heterocyclic compounds including highly substituted thiophene derivatives, benzo[ b ]thiophene, E ‐3‐aroylidene‐2‐oxindole derivatives, 1,3,4‐thiadiazine scaffolds, functionalized 1,2,3‐thiadiazoles, pyrazolo[3,4‐ c ]quinolones, and tetrahydropyrazine scaffold . Also, triethylammonium thiolates have been used as sulfenylating agents in sulfenylation ,…”