As shown by pentaquadrupole triple‐stage mass spectrometric and 18O‐labeling experiments, two seven‐membered cyclic acetals, 1,3‐dioxepane and 1,3‐dioxep‐5‐ene, fail to react by transacetalization with the gaseous acylium ions CH3C+=O and (CH3)2NC+=O. Instead, a novel and less exothermic but more kinetically favored reaction, seven‐to‐five ring contraction, occurs predominantly, and to great extents with the most reactive acylium ion, (CH3)2NC+=O. 1,3‐Dioxepane yields O‐acylated tetrahydrofurans; 1,3‐dioxep‐5‐ene yields O‐acylated 2,5‐dihydrofurans.
|Journal||Journal of Mass Spectrometry|
|Publication status||Published - 1999|
|MoE publication type||A1 Journal article-refereed|