Diethyl (2-bromo-l- phenyl, vinyl) phosphonite and diethyl (1-chloro-l-phenyl, vinyl) phosphonate react with diazomethane, diphenyldiazomethane, and phenylbenzoyldiazomet- hane. The reaction with diazomethane goes by 3 ' 2 “ 5 scheme of dipolar cycloaddition. The reaction of the phosphonite with diphenyldiazomethane goes by the 3-3-6 scheme, while in the case of phosphonate cleavage of C-P bond took place. However, the reaction of phospho-nate with pheriylbenzoyldiazomethane goes by 3 -- 2 — 5 scheme of 1, 3-dipolar cycloaddition with. the cleavage of C-P bond. .