Electron-Impact Mass-Spectra of 3-Alkyl-2,1-benzisoxazoles

Abstract

3-Alkyl-2,1-benzisoxazoles underwent complex fragmentations under electron impact, and the balance between available pathways changed considerably across the range of alkyl groups (methyl, ethyl, isopropyl and t-butyl). The primary loss of CO is accounted for in terms of rearrangement of the initial molecular ion to an alkylimine ketene species.

The 3-methyl compounds lost methyl as methyl cyanide, acylium cation or ketene, but the higher alkyl groups were chiefly lost as alkyl cations or by internal fragmentations in which some novel ortho-effects were noted. Most of these pathways were confirmed by B/E linked scans, and useful comparisons were made with the e.i . spectra of N- alkylanthranilic acids.

All of these isoxazoles underwent partial decomposition on the heated probe.