Unusual collision-induced fragmentations of deprotonated methoxybenzyl formates in the gas phase. 1,2-Wittig rearrangements, cross-ring nucleophilic substitution and ortho effects

Eur. J. Mass Spectrom. 4, 113–119 (1998)
DOI: 10.1255/ejms.197

Unusual collision-induced fragmentations of deprotonated methoxybenzyl formates in the gas phase. 1,2-Wittig rearrangements, cross-ring nucleophilic substitution and ortho effects

Mark S. Taylor, Suresh Dua and John H. Bowie
Department of Chemistry, The University of Adelaide, South Australia, 5005, Australia.

ABSTRACT:

Deprotonated benzyl formate undergoes loss of carbon monoxide via the rearrangement sequence Ph-^–CHOCHO ® PhCH(O^–)CHO ® [(PhCHO) HCO^–] ® PhCH2O^– + CO. The last step involves a 1,2-Wittig anionic rearrangement involving hydride transfer from a formyl anion. When a methoxyl group is placed on the benzene ring, the Wittig rearrangement competes with a cross-ring S_N2 process, i.e. [(o-, m– or p– MeOC₆H₄CHO) HCO^–] ® o-, m– or p– OHCC₆H₄O^– + MeCHO and/or (CH₄ + CO). The ortho-isomer also undergoes several ortho-effects including loss of MeOH to produce [PhCOCHO – H]^–.

Keywords: Negative ions, deprotonated methoxybenzyl formates, 1,2-Wittig rearrangement, nucleophilic substitution, ortho-effects.

You can buy this paper on-line in PDF format; it costs only £11.75. Just click on the BUY on-line button. You can pay on-line through a secure server and get access immediately.