Stereoselective Chemical Ionization Mass Spectrometry: Reactions of CH 3 OPOCH 3 + with Cyclic Vicinal Diols

The phosphenium ion CH 3 OPOCH 3 + readily attacks hydroxyl groups of neutral substrates in the gas phase in a Fourier-transform ion cyclotron resonance mass spectrometer. The electrophilic character of CH 3 OPOCH 3 + is in agreement with molecular orbital calculations (Becke3LYP/6-31G(d) + ZPE) that predict a singlet electronic ground state for this species. The observed reactions provide a convenient synthetic route to various larger phosphenium ions in the gas phase. Most importantly, however, CH 3 OPOCH 3 + was found to be extremely sensitive to the stereochemical structure of the neutral substrate. The dramatically different reaction product distributions obtained for diastereomeric cyclic vicinal diols suggest that CH 3 OPOCH 3 + provides a powerful chemical ionization reagent for the mass spectrometric determination of the stereochemistry of diols.