Light‐Induced Tetrazole‐Quinone 1,3‐Dipolar Cycloadditions

Abstract

Quinones were firstly used as dipolarophiles in a photoclick 1,3‐cycloaddition with 2,5‐diaryltetrazoles, as photoactivatable predipoles, providing a novel and efficient access to three types of pyrazole‐fused quinones (indazoledione derivatives). Distinctive features of this protocol include the use of light as the unique reagent and readily available, stable, and easy to handle starting materials and good to excellent yields. Photophysical and electrochemical properties of the quinones and their potential application as photoredox catalysts are also detailed.

A straightforward conversion of 1,4-quinones into polycyclic pyrazoles via [3 + 2]-cycloaddition with fluorinated nitrile imines

“…This type of cycloaddition attracted considerable attention of other groups [ 18 – 19 ] and recently has been applied for the preparation of some π-extended pyrazole derivatives, which exhibited promising biological activity [ 20 ].…”

Microscopic mechanism of light-induced tetrazole-quinone 1,3-dipolar cycloaddition: a MS-CASPT2 theoretical investigation

“…9 At the same time, some can also be employed as organic photocatalysts, such as 1,3-bis(4-methoxyphenyl)-1H-benzo[f] indazole-4,9-dione, to participate in the photooxidation process. 10 In addition, they may have a potential uorescence 10 and are used for optical attachment and light labeling of biomolecules. [11][12][13] Currently, the commonly used methods for synthesizing such pyrazoquinones are: (1) under a certain condition, 1,3-dipolar cycloaddition between diazomethane and benzoquinone; (2) the intermediate of diazopropane and appropriate benzoquinone or naphthoquinone derivatives by 1,3-dipolar cycloaddition in the mixture of THF/Et 2 O at room temperature; 14 (3) the benzoquinone analogues and N,Ndisubstituted hydrazone undergo a similar Michael addition rst, and then get through the closing loop aer peroxidation or high heat; 15 (4) at room temperature and alkaline conditions, the corresponding arylhydrazone acyl chlorides or their nitrile imine reacts with the benzoquinone derivatives to obtain monocyclic or bicyclic adducts.…”

“…Recently, Ortiz-Rojano et al have proposed a method that uses light as the only reagent to induce the light-licking reaction of tetrazole-quinone to synthesize a series of potential pharmacological pyrazoquinones, which arouses great interest. 10 At room temperature in the open air, ethyl acetate as the solvent, high-pressure ultraviolet lamp as the radiation source, and equimolar mixing of the reactants as the optimum reaction conditions, the experiment uses different photoactivatable 2,5-disubstituted tetrazoles (synthesized from different arylsulfonyl hydrazides and diazonium salts, and is the main light absorber) to react with 1,4-naphthoquinone to obtain a higher yield (50–95%) of various types of monoadditive pyrazoquinones. The formation of pyrazoquinone involves the photogeneration of nitrile imine dipole, followed by 1,3-dipolar cycloaddition with 1,4-naphthoquinone and enolization, and finally maybe oxidized by naphthoquinone and air in the last step (the structure of hydronaphthoquinone reduction of the product has not been observed throughout).…”

The Quest for the Right Trade‐Off for an Efficient Photoclick Monitoring Reaction

“…The product has been fully characterized according to the literature. [29] General procedure for synthesis of arendiazonium salts: For the synthesis of arendiazonium salts, 2 ml of 37 % HCl were added to a cooled solution of the aniline (7.3 mmol, 1 eq.) in 10 ml of 50 % ethanol solution.…”

“…Characterization of T2 and T6 have been previously reported. [29,30] T1: Yield (%) = 30 % (brown solid) . 1 H-NMR (300 MHz, DMSO-d 6 ) δ ppm 10.05 (s, 1H), 8.05-7.97 (m, 4H), 7.02 (d, J = 8.95 Hz, 2H), 6.9 (d, J = 8.49 Hz, 2H), 3.86 (s, 3H).…”