New synthetic approach to pyrazolo[1,5‐<scp><i>a</i></scp>]pyrazine derivatives from 2,2‐dichlorovinylacetophenones

New efficient synthetic methods in pyrazoline and pyrazolopyrazine chemistry have been developed starting from 2,2-dichlorovinylacetophenones 1, which were sequentially transformed into 3-aryl-5-dichloromethyl-1-(2-hydroxiethyl)-2-pyrazolines 2, 3-aryl-5-dichloromethyl-1-(2-O-tosylhydroxyethyl)-2-pyrazolines 3, 3-aryl-5-dichloromethyl-1-(2-azidoethyl)-2-pyrazolines 4, 3-aryl-5-dichloromethyl-1-(2-aminoethyl)-2-pyrazoline hydrochlorides 5, by reaction with 2-hydroxyethylhydrazine, O-tosylation, azidation, catalytic hydrogenation, respectively. Compounds 5 treated aqueous sodium hydroxide to provide 2-aryl-4,5,6,7-tetrahydropyrazolo[1,5-a]pyrazines 6 one-step conversions involving cyclization aromatization. A mechanism has proposed the aid of DFT theoretical calculations. could also be obtained directly one-pot reactions tosylates 3 ammonium followed addition hydroxide. The molecular structure 2-(4-chlorophenyl)-4,5,6,7-tetrahydropyrazolo[1,5-a]pyrazine 6c was determined X-ray crystallography. Simplicity, good overall yields inexpensive materials are advantageous features improved procedures reported herein.