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

ortho effects

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Eur. J. Mass Spectrom. 4, 113 - 119 (1998)

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.

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