Ion-molecule reactions between the O=P(OCH3)2+phosphonium ions and ethyl 3,3-dimethylacrylate has been investigated by quadrupole ion trap mass spectrometeryEthyl 3,3-dimethylacrylate was used in the synthesis of: . 3-benzylmercupto-3-methylbutanoic acid ethylester . cis-2-cyano-3,3-dimethylcyclopropanecarboxylic acid, precursor for the synthesis of cis-pyrethroids . 1-[13CD3]-9-cis-retinoic acid Ion-molecule reactions between the O=P(OCH3)2+phosphonium ions and ethyl 3,3-dimethylacrylate has been investigated by quadrupole ion trap mass spectrometery Ethyl 3,3-dimethylacrylate was used in the synthesis of: . 3-benzylmercupto-3-methylbutanoic acid ethylester . cis-2-cyano-3,3-dimethylcyclopropanecarboxylic acid, precursor for the synthesis of cis-pyrethroids . 1-[13CD3]-9-cis-retinoic acid