Stereoselective chemical ionization mass spectrometry: Reactions of CH3OPOCH3+ with cyclic vicinal diols

The phosphenium ion CH3OPOCH3+ readily attacks hydroxyl groups of neutral substrates in the gas phase in a Fourier-transform ion cyclotron resonance mass spectrometer. The electrophilic character of CH3OPOCH3+ 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, CH3OPOCH3+ 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 CH3OPOCH3+ provides a powerful chemical ionization reagent for the mass spectrometric determination of the stereochemistry of diols.