UNUSUAL COLLISION-INDUCED FRAGMENTATIONS OF DEPROTONATED METHOXYBENZYL FORMATES IN THE GAS-PHASE - 1,2-WITTIG REARRANGEMENTS, CROSS-RING NUCLEOPHILIC-SUBSTITUTION AND ORTHO EFFECTS

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 rearrange ment involving hydride transfer from a formyl anion, When a methoxyl g roup is placed on the benzene ring, the Wittig rearrangement competes with a cross-ring S(N)2 process, i,e, [(o-, m- or p-MeOC6H4CHO)HCO-] - -> o-, m- or p-OHCC6H4O- + MeCHO and/or (CH4 + CO). The ortho-isomer a lso undergoes several ortho-effects including loss of MeOH to produce [PhCOCHO-H](-).