Reaction of 3-methyl-5-pyrazolones with carbon disulfide and alkyl bromides under phase-transfer catalysis to give alkyl 5-hydroxy-3-methyl-1H -pyrazole-4-carbodithioates is described. Using 1,2-dibromoethane or 1,3-dibromopropane, the corresponding cyclic ketene dithioacetals are formed.