3-Alkenyl-5-chloropyrazoles: expedient synthesis via heterocyclization of 1,1-dichloro-4-halo-1-alken-3-ones with hydrazines

Novel directed synthesis of functionalized pyrazole derivatives via regioselective solvent-free thiylation of 3-alkenylpyrazoles with arenethiols

“…Yields of the target pyrazoles calculated from starting acyl chlorides 1, and the synthesis of 3-vinylpyrazoles 4a,b were described in our previous publication; 28 pyrazole 4g was obtained as a mixture of E-and Z-isomers in a 4:1 ratio. The reactions of 2,2-dichlorovinylketone 2a with dimethylhydrazine and benzylhydrazine, synthesis of intermediate 3-(1-chloroethyl)pyrazoles 3a,b and final 3-vinylpyrazoles 4a,b were also described in the previous paper.…”

“…The reactions of 2,2-dichlorovinylketone 2a with dimethylhydrazine and benzylhydrazine, synthesis of intermediate 3-(1-chloroethyl)pyrazoles 3a,b and final 3-vinylpyrazoles 4a,b were also described in the previous paper. 28 The reactions of dichlorovinylketones 2a,b with other hydrazines, the reactions of ketones 2c,d with dimethylhydrazine, and the synthesis of pyrazole derivatives 3c-j and 4c-g are presented here for the first time.…”

“…Synthesis of 2,2-dichlorovinylketones 2a-d, 3-(1-chloroethyl)pyrazoles 3a,b, and 3-vinylpyrazoles 4a,b was presented in a previous paper. 28 Pyrazole derivatives 3c-j and 4c-g are described here for the first time.…”

“…[1][2][3][4][5][6][28][29][30][31][32][33][34][35][36][37][38][39] The chemical transformations of alkenylpyrazoles are still poorly understood. It is known that N-alkenyl-and some 4-alkenylpyrazoles can participate in polymerization, 21,29 complex formation, 30,31 thiylation, 32 and cycloaddition.…”

“…It is known that N-alkenyl-and some 4-alkenylpyrazoles can participate in polymerization, 21,29 complex formation, 30,31 thiylation, 32 and cycloaddition. [33][34][35] Imidoalkylation of 1-, 3-, 4-, and 5-vinylpyrazoles with N-(2,2,2-trichloroethylidene)ethoxycarbonylamines is also reported 34,36 Chemical transformations of the difficult-to-access 3-alkenylpyrazoles 36-38 and 3-alkenyl-5-chloropyrazoles 28 are even less studied and only very few reactions with oxygen and sulphur nucleophiles have been published. 39,40 We have recently developed methodology for the preparation of hitherto unknown 3-alkenylpyrazoles, 28 possible building blocks for the directed synthesis of substances and materials for advanced technologies, from the corresponding 3-haloalkyl pyrazoles.…”