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

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 SN2 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]-.