Intramolecular reactions. An explanation for [M−H]+ ions in the chemical ionization mass spectra of some ring C-substituted methyl dehydroabietate derivates

Abstract

The formation of [M−H]+ ions in the chemical ionization mass spectra of ring C-substituted methyl dehydroabietates, when methane is used as reagent gas, has been investigated. Two mechanisms, one involving H2 loss from [M−H]+ ions, and the other, hydride ion transfer reactions to the methane reagent ions, have been proposed to account for [M−H]+ ion abundances. For methyl 12,14-diaminodehydroabietate, protonation of the amino group on C-14, followed by the loss of H2 by an intramolecular reaction via a cyclic transition state, is proposed as the predominant mechanism. Hydride ion transfer from the benzylic C-7 has been suggested to provide a major contribution to the formation of [M−H]+ ions of methyl 12-amino-14-nitrodehydroabietate. These conclusions are also consistent with results obtained using ammonia as reagent gas. © 1997 John Wiley & Sons, Ltd.