Haloacetylated enol ethers: 16[5] regiospecific synthesis of 5-trichloromethyl-pyrazoles

The regiospecific synthesis and isolation of three series of 5-trichloromethyl-pyrazoles 2f-j, 3a-j and 4a-j from the cyclo-condensation of 1,1,1-trichloro-4-alkoxy-3-alken-2-ones (1a-f) or trichloroacetyl containing beta-diketones (1g-j) with dry hydrazine and phenyl-hydrazine is reported. It was established by H-1- and C-13-NMR spectroscopy that the 5-hydroxy-5-trichloromethyl-4,5-dihydro-1H-pyrazole intermediates 2a-j were formed quantitatively.