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ORIGINAL PAPER

I2/KI‑Catalyzed synthesis of 5‑trifluoromethylated 1,2,4,6tetrazepine‑3‑thiones by annulation of trifluoroacetimidoyl chlorides and thiosemicarbazones Ali Darehkordi1 · Farzaneh Nejad Khorasani1 · Marziyeh Mohammadi1 · Elham Kazemi1 Received: 21 March 2020 / Accepted: 22 October 2020 © Springer-Verlag GmbH Austria, part of Springer Nature 2020

Abstract  An efficient and simple protocol for the synthesis of trifluoromethylated 1,2,4,6-tetrazepines by intramolecular crosscoupling of C(sp2)–H and N–H bonds using I­ 2/KI catalyst under aerobic oxidative has been demonstrated. This research exhibited a nucleophilic substitution reaction and then oxidative cyclization between trifluoroacetimidoyl chlorides and thiosemicarbazones. Graphic abstract

Keywords  5-Trifluoromethylated 1,2,4,6-tetrazepine-3-thiones · Trifluoroacetimidoyl chlorides · Thiosemicarbazones · C–N bond formation

Introduction Tetrazepine derivatives are important seven-membered azaheterocyclic compounds that occupy a significant position in medicinal and pesticide chemistry [1]. Although tetrazepine derivatives are very interesting for chemists and pharmacists, there are limited methods for synthesis of these compounds. Due to the importance of tetrazepine in the pharmaceutical and wide range of applications [1, 2], synthesis of new tetrazepines and also new methods, much attention has Electronic supplementary material  The online version of this article (https​://doi.org/10.1007/s0070​6-020-02703​-5) contains supplementary material, which is available to authorized users. * Ali Darehkordi [email protected]; [email protected] 1



Department of Chemistry, Vali-e-Asr University, Rafsanjan 77176, Iran

been paid recently. For example, copper(II)-catalyzed enantioselective 1,3-dipolar [3 + 4] cycloaddition of azomethine imines with in situ-formed azoalkenes [3], transformations of [1,2,4]triazolo[4,3-b][1,2,4,5]tetrazines by action of C nucleophiles have been established, that these reactions are initiated by nucleophilic attack at the ring nitrogen atom, the ring opening of the tetrazine ring followed by recyclization provide new opportunities for construction of [1,2,4]triazolo[4,3-b][1,2,4,6]-tetrazepines [4], reaction of 4-amino-6-benzyl-3-hydrazinyl-1,2,4-triazin-5(4H)-one with isatin in DMF and/or absolute ethanol in the presence of few drops of piperidine and then ring closure of 4-amino-6-benzyl-3[(2-hydroxy-3H-indol-3-ylidene)hydrazono]-3,4-dihydro-1,2,4triazin-5(2H)-one [5] and reaction of 1,2-dialkyldiaziridines with benzoyl isothiocyanate at the room temperature in the presence of ionic liquids ­[emim][BF4] and ­[emim][PF6] by the cleavage of the C–N and of the N–N bonds of the diaziridine ring [6] are some of the important methods for synthesis of these compounds.

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A. Darehkordi et al.

The trifluoromethyl group (­ CF3) is one of the most common fluorinated substituents in medicinal, agricultural, and material sciences [7] as it offers simultaneously high lipophilicity, an elevated electron d