Neighboring-Group Participation in the Gas Phase. Loss of benzaldehyde from [(benzyloxy)methyl]dialkylsilyl-substituted 1,3-dithianes

[(Benzyloxy)methyl]dialkylsilyl‐substituted 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 process, where a hydride is proposed to be transferred from the benzyl position to a neighboring thionium ion. This would form a particle that could readily lose benzaldehyde as a neutral fragment. The CI‐MS results provide an explanation for the unusual instability of (benzyloxy)methyl‐substituted silanes towards acids. In fact, the formation of benzaldehyde was established in the decomposition of a (benzyloxy)methyl‐substituted acylsilane in the presence of Lewis or Brønsted acids and ethanethiol. The CI‐MS study, therefore, represents a useful method to recognize unusual reactions that are – or might be – important in solution.