Fluoroalkadienes were prepd. by Zn-catalyzed ring cleavage of 1-chloro-1-fluoro-2-halomethylcyclopropanes, obtained by treating haloalkenes with FCHCl2. Thus, ClCH2CH:CMeEt was treated with FCHCl2 to give the cyclopropane I (R = Cl) which was iodinated to give I (R = iodo). Treatment of the latter compd. with Zn gave CH2:CHCF:CMeEt. The fluorocycloheptadiene II was similarly obtained. [on SciFinder (R)]