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Abstract
Tetraesters of dihalogenomethylenebisphosphonic acids undergo nucleophilic dehalogenation with potassium fluoride or hydroxide in solution in acetonitrile in the presence of [18,6]-crown ether. Fluoride ion is the best nucleophile for dehalogenation and there is no evidence for nucleophilic displacement of halide ion by attack at the central atom of the methylenebisphosphonic esters. Conditions have been developed for the monodehalogenation of tetraisopropyl dibromo- and dichloromethylenebisphosphonates in good yield.