The reactions of dimethyl 1-hydroxycycloalkylphosphonates having a five- to seven-membered ring with sulfuryl chloride and phosphoruspentachloride afforded olefinic and/or dichloro derivatives of phosphonates. The mechanism of the formation of new dichloro derivatives and the reactions of dimethyl 1-methylethylphosphonate with sulfuryl chloride and phosphoruspentachloride were also investigated.