Mechanistic study of reversible solid-state melt isomerization of 2-oxindoles to 2-quinolinones and its occurrence in a mass spectrometer

• Published in: Journal of molecular structure 2019-01, Vol.1175, p.828-835
• Main Authors: Martínez-Gudiño, Gelacio, Pérez-Rojas, Nadia A., Trujillo-Serrato, Joel J., Mora-Pérez, Yolanda, Suárez-Castillo, Oscar R., Morales-Ríos, Martha S.
• Format: Article
• Language: English
• Subjects: Isotopic labeling; Mass spectrometry; Oxindoles; Quinolinones; Solid state melt reaction
• ISSN: 0022-2860; 1872-8014
• DOI: 10.1016/j.molstruc.2018.08.056

An eco-friendly equilibrated rearrangement of a series of 2-oxo-3-indolyl acetic acids (1) with 2-oxo-1,2,3,4-tetrahydroquinoline-4-carboxylic acid derivatives (2) was investigated through a solid state melt reaction (SSMR). Mechanistic insight into the thermal rearrangement is provided by 13C-isotopic labeling. The standard mass spectra of 1 and 2 were virtually identical preventing their reliable identification. Reversible interconversion of 1 and 2 was evidenced to occur in the inlet system of a mass spectrometer under electron impact conditions. Relative abundances of fragment ions were found to be a function of temperature. [Display omitted] •An equilibrated thermal rearrangement of oxindoles to quinolinones was performed under solid-state melt conditions.•The molecular rearrangement was also induced by electron impact mass spectrometry.•The relative abundance of specific product ions in the mass spectra allowed isomeric differentiation.•Mechanistic proposal was supported by 13C labeling experiments.