Haloacetylated enol ethers. 11. Synthesis of 1-methyl- and 1-phenyl pyrazole-3(5)-ethyl esters. A one-pot procedure

A one-pot synthesis of 1-methyl- and 1-phenylpyrazole-3(5)-ethyl esters 2,3 a-e by the cyclocondensation of beta-alkoxyvinyl trichloromethyl ketones 1a -e with methyl and phenyl hydrazine hydrochloride under mild conditions, is reported. A study using compounds 1a-e with different substituents proved that these are versatile building blocks for the synthesis of pyrazole deri vatives, having a 3(5)-ethoxycarbonyl substituent in good yields (60-89%). The hydrazine and beta-alkoxyvinyl trichloromethyl ketone substituent effec ts on the reaction regiochemistry on the formation of the 1,3- and 1,5-isom er were observed.