The present invention provides a process for the preparation of a compound of formula i:wherein R1 is C1-C4haloalkyl； R2 is optionally substituted alkyl, optionally substituted aryl or optionally substituted heteroaryl； and R3 is methyl or ethyl； comprising reacting a compound of formula IV:wherein Rl, R2 and R3 are as defined for the compound of formula I； with an alkylating agent in the presence of an amide.本發明提供一種製備式I化合物之方法：其中R1為C1-C4鹵烷基；R2為視情況經取代之烷基、視情況經取代之芳基或視情況經取代之雜芳基；且R3為甲基或乙基；其包含使式IV化合物：其中R1、R2及R3如關於式I化合物所定義；與烷基化劑在醯胺存在下反應。
