Indole and Pyrrole Derivatives as Pre-photocatalysts and Substrates in the Sulfonyl Radical-Triggered Relay Cyclization Leading to Sulfonylated Heterocycles

Abstract

A visible-light-induced method for the construction of heterocyclic scaffolds such as pyrido[1,2-a]indoles and indolizines via sulfonyl radical-triggered relay cyclization without employing any external photocatalyst has been developed. Preliminary mechanistic investigation indicated that indole and pyrrole derivatives could serve as pre-photocatalysts to promote the sulfonylation/cyclization, thereby providing a facile method to synthesize valuable sulfonylated heterocycles.

The Application of Sulfonyl Hydrazides in Electrosynthesis: A Review of Recent Studies

“…The researchers proposed a mechanism based on cyclic voltammetry (CV) experiments and radical trap experiments, indicating that the sulfonyl hydrazide (10) was first oxidized at the anode, and the N-centered radical (14) was subsequently formed. Then the radical (14) underwent the loss of nitrogen and gave a sulfonyl radical (15), which added to the C�C double bond in the following step and generated the carbocation intermediate (16).…”

“…48 In the research, a three-component reaction was carried out in an undivided electrolytic cell charged with a carbon rod anode and a nickel plate cathode with a constant current of 12 mA at room temperature using CH 3 CN as solvents and nBu 4 NBF 4 (0.1 mmol) as an electrolyte. Under the reaction conditions, sulfonyl hydrazides (10) reacted with alkenes (11) and alcohols (12) to generate β-alkoxyl-substituted sulfones (13) with good yields, giving hydrogen and nitrogen gas as the byproducts. Various conditions were attempted when exploring the research, researchers employed a current of different levels, electrode materials, electrolytes, solvents, and amount of methanol; finally, the reported standard conditions were found to be optimal, and nBu 4 NBF 4 was found to be the key factor.…”

“…In the Shapiro reaction , and variation of the Wolff–Kishner–Huang Minlon reduction reaction, TsNHNH 2 was chosen to reduce the carbonyl group (CO) to the methylene (CH 2 ) (Scheme ). In chemical reactions, sulfonyl hydrazides are viewed as alternatives to sulfinic acids and their salts , or sulfonyl halides, − and are broadly used in organic transformations , or syntheses of active pharmaceutical substances . Compared with other sulfonic derivatives or sulfonyl halides, sulfonyl hydrazides are easy to handle, stable, moisture-compatible, and noncorrosive.…”

Synthesis of pyrido[1,2-a]indol-6(7H)-ones via a visible light-photocatalyzed formal (4 + 2) cycloaddition of indole-derived bromides and alkenes or alkynes

“…Yang and co-workers reported a method for the construction of pyridine[1,2- a ]indole and indolizines under visible light (Scheme 1, eqn (1)). 37 Hull and co-workers reported a copper-catalyzed inter-molecular difunctionalization of alkenes, α-bromoalkyl esters and indoles. 38 Inspired by these studies and due to our continuous efforts devoted to photochemical reactions, we presented a visible-light-induced intermolecular cyclization of alkenes for the synthesis of pyrido[1,2- a ]indol-6(7 H )-ones under mild conditions (Scheme 1, eqn (2)).…”

Visible Light Promotes Cascade Trifluoromethylation/Cyclization, Leading to Trifluoromethylated Polycyclic Quinazolinones, Benzimidazoles and Indoles

“…The following supporting information can be downloaded at: , Experimental details and characterization data for products 3a – 3x , 5a, 5b, 5e – 5h and 7a − 7j [ 42 , 46 , 47 , 49 , 50 , 51 ].…”