Gas-phase reactions of stereoisomeric cyclic diols with CH 3 OB + OCH 3 were examined in a small Fourier transform ion cyclotron resonance mass spectrometer. CH 3 OB + OCH 3 is a strong electrophile and rapidly abstracts an OH group from the diols studied. This very exothermic reaction is followed by spontaneous fragmentation of the resulting ion. In addition to this reaction, cis-diols also react with CH 3 OB + OCH 3 by an intramolecular displacement of CH 3 OH in the initially formed, short-lived adduct ion. The product distributions allow distinction between the cis- and trans-isomers of 1,2-cyclopentanediol, and between the cis- (diendo- and diexo-) and trans-isomers of 2,3-trinorbornanediol.