First (3+2)-Cycloadditions of Thiochalcones as C=S Dipolarophiles: Efficient Synthesis of 1,3,4-Thiadiazoles via Reactions with Fluorinated Nitrile Imines

Abstract

Pyrazole 10a 28 Exemplary 1 H NMR data of thiochalcone 2f (mixture of dimers) 30 X-ray data of pyrazole 10a 31 Attempted reaction of thiochalcone 2a with the non-fluorinated nitrile imine 12 33

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

“…In a series of our recent publications, efficient syntheses of fluoromethylated five-and six-membered N,S-heterocycles, such as 5 and 6, available via [3 + 2]-cycloadditions [21][22][23][24][25] or [3 + 3]-annulations [26] of trifluoroacetonitrile imines 7, respectively, were reported (Scheme 2).…”

First thia-Diels–Alder reactions of thiochalcones with 1,4-quinones

“…Aryl and hetary lthiochalcones 1a – d are easily obtained by treatment of the corresponding chalcones with Lawesson′s reagent in THF solution [15]. Along with the commercially available 1,4-benzoquinone ( 2a ) and 1,4-naphthoquinone ( 2b ), 1,4-anthraquinone ( 2c ) and 5-chloro-10-hydroxy-1,4-anthraquinone ( 2d ) were prepared from quinizarine according to known procedures [27–28].…”

“…Despite the fact that thiochalcones exist in solution as mixtures of dimers [15–16], they enter into cycloaddition reactions not only as heterodienes [17–19], but also as heterodipolarophiles [15]. In two recent publications we reported new thia-Diels–Alder reactions of aryl, hetaryl and ferrocenyl-substituted thiochalcones with acetylenic dienophiles, which lead to the corresponding 4 H -thiopyrans in a regioselective manner [16,20].…”

Synthesis of fused 3-trifluoromethyl-1,2,4-triazoles via base-promoted [3 + 2] cycloaddition of nitrile imines and 1H-benzo[d]imidazole-2-thiols

“…11 The Jasiński group developed a strategy for the efficient synthesis of 1-aryl-3-trifluoromethylpyrazoles in one-pot, using nitrile imines and mercaptoacetaldehyde as the raw materials (Scheme 1a). 12 Although many methods for the synthesis of valuable five-membered moieties via a [3 + 2] cycloaddition strategy employing trifluoromethyl-substituted nitrile imines 13 and fused triazoles 14 have been disclosed, the direct route towards fused 3-trifluoromethyl-1,2,4-triazoles, which is available with limited methods, is rarely investigated and still high in demand. Based on the significant value of such backbones 15 and traditional conditions usually used in base-promoted [3 + 2] dipolar cycloaddition involving 2-mercapto or 2-methylthio 1 H -benzoimidazole derivatives, 16 herein, we present a novel route to access fused 3-CF 3 -1,2,4-triazoles which possibly show pharmacological activity in high efficiency using 1 H -benzo[ d ]imidazole-2-thiol 1 and fluorinated nitrile imines 2 under the promotion of a base (Scheme 1b).…”