| 摘要 |
A method of preparing certain dihalogen vinyl cyclopropane carboxylic acid esters of the formula <IMAGE> I wherein R is an alkyl moiety and X is chlorine or bromine by exposing a dihalogen vinyl dihydrofuran of the formula <IMAGE> II to light, e.g., ultraviolet light. Also disclosed is a method for preparing such 2,4,4-trimethyl-3-carbalkoxy-5-( beta beta -dihalogenvinyl)-4,5-dihydrofurans by reaction of a beta -alkoxycrotonic acid ester or 3,3-bisalkoxybutyric acid ester with a 1,1,1-trihalogen-4-methyl-3-or -4-pentene-2-ol in the presence of an acid catalyst. Also disclosed is a method of converting such 2,4,4-trimethyl-3-carbalkoxy-5-( beta , beta -dihalogenvinyl)-4,5-dihydrofuran by thermal rearrangement into 2,5,5-trimethyl-3-carbalkoxy-4-( beta , beta -dihalogenvinyl)-4,5-dihydrofurans. Such 2,4,4- and 2,5,5-trimethyl-3-carbalkoxy-5-( beta , beta -dihalogenvinyl)-4,5-dihydrofurans are new.
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