A facile preparation of trans-1,2-cyclopropanes containing p-trifluoromethylphenyl group and its application to the construction of pyrazole and cyclopropane ring fused pyridazinone derivatives

A facile methodology for the preparation of highly functionalized trans-1,2-cyclopropanes containing p-trifluoromethylphenyl group 3 is described. Arsonium bromides 1 reacted with electron-deficient olefins 2 in the presence of K2CO3 to provide 3 stereoselectively in moderate to good yields. This process has been successfully applied to the construction of cyclopropane ring fused pyridazinone derivatives 4 or pyrazole derivatives 5.