Intramolecular aromatic substitution and amino-Claisen rearrangement in substitutedN-(2-propynyl)anilines on electron impact
作者:D. V. Ramana、M. S. Sudha
DOI:10.1002/jms.1190300713
日期:1995.7
N-(2-Propynyl)anilines undergo amino-Claisen rearrangement to a minor extent in the ion source, losing a molecule of HCN under electron impact conditions. However, metastable molecular ions with energies closer to threshold undergo Claisen rearrangement giving rise to more abundant [M − HCN]+· ions in the first field-free region. Loss of a hydrogen from the molecular ion gives rise to the base peak in the mass spectrum of N-(2-propynyl)aniline. The hydrogen that is expelled for the formation of the [M − H]+ ion is observed to be from the amino nitrogen, propargylic carbon and the ortho-carbon of the ring. The last process leads to a cyclic fragment involving intramolecular aromatic substitution. Double oxygen migration from the nitro group to the triple bond, due to the ortho effect, yields an abundant ion at m/z 105 in N-(2-propynyl)-o-nitroaniline. The proposed fragmentation pathways and ion structures are substantiated by high-resolution data, B/E and B2/E linked-scan spectra, collisionally activated dissociation–B/E linked-scan spectra and deuterium isotopic labelling.
N-(2-炔丙基)苯胺在离子源中会发生少量的氨基克莱森重排反应,在电子轰击条件下失去一分子HCN。然而,能量接近阈值的亚稳态分子离子会经历克莱森重排,在第一个无场区域产生更丰富的[M-HCN]+·离子。从分子离子中失去一个氢原子会在N-(2-炔丙基)苯胺的质谱中形成基峰。形成[M-H]+离子的氢原子来自氨基氮、炔丙基碳和环的邻位碳。最后一个过程导致形成涉及分子内芳香取代的环状碎片。由于邻位效应,硝基中的双氧向三键迁移,在N-(2-炔丙基)-邻硝基苯胺中产生m/z 105的丰富离子。所提出的碎裂途径和离子结构通过高分辨数据、B/E和B2/E链扫描谱、碰撞诱导解离-B/E链扫描谱和氘同位素标记得到证实。