NEIGHBORING-GROUP PARTICIPATION IN THE GAS-PHASE - LOSS OF BENZALDEHYDE FROM [(BENZYLOXY)METHYL]DIALKYLSILYL-SUBSTITUTED 1,3-DITHIANES

[(Benzyloxy)methyl]dialkylsilyl-substitued 1,3-dithianes show in CI-MS an abundant loss of benzaldehyde from the [M + H](+) quasi-molecular ion. The fragmentation is explained with an intramolecular redox proce ss, where a hydride is proposed to be transferred from the benzyl posi tion to a neighboring thionium ion. This would form a particle that co uld readily lose benzaldehyde as a neutral fragment. The CI-MS results provide an explanation for the unusual instability of (benzyloxy)meth yl-substituted silanes towards acids. In fact, the formation of benzal dehyde was established in the decomposition of a (benzyloxy)methyl-sub stituted acylsilane in the presence of Lewis or Bronsted acids and eth anethiol. The CI-MS study, therefore, represents a useful method to re cognize unusual reactions that are - or might be - important in soluti on.