Mass spectra of tetrahydroisoquinolines: a novel concerted fragmentation

Abstract

An unusual fragmentation of 92 mass units from the parent ion of an 8-benzyloxytetrahydroisoquinoline is due to loss of the elements of toluene by concerted cleavage of the benzyl group and a hydrogen atom from the 1-position; this is confirmed both by the appearance of a metastable ion for the overall process, by deuterium labelling of the 1-position, and by the absence of a corresponding peak in the spectrum of a 7-benzyloxytetrahydroisoquinoline. Deuterium labelling also confirms that the M- 1 peak commonly observed in the mass spectra of tetrahydrosio-quinolines is due to cleavage of a hydrogen atom from the 1-position; high-resolution measurements have confirmed the nature of the other major primary fragmentation processes.