THE COMPLEX ANIONIC REARRANGEMENTS OF DEPROTONATED ALPHA-OXIMINO CARBONYL DERIVATIVES IN THE GAS-PHASE

Alpha-oximino ketones R1COC(NOH)R2 deprotonate preferentially to form R1COC(NO-)R2 and this anion decomposes by a variety of complex rearrangement processes. The two major fragmentations involve the following overall processes (i) and (ii). [GRAPHICS] It is proposed that reaction (i) involves a four-centre reaction of O- at the carbonyl carbon. No evidence of a Beckmann-type rearrangement is indicated for alpha-oximino ketones. The corresponding deprotonated alpha-oximino ketone O-methyl ethers also fragment by complex rearrangement. For example, MeCOC(NOMe)Me deprotonates to form two ions which are interconvertible on collisional activation. The enolate ion is the principal deprotonated species, and it decomposes by the overall process -CH2COC(NOMe)Me --> -CH2CN + CH2CO + MeOH. The other anion decomposes by loss of methanol. This is best rationalised either by the Beckmann process MeCOC(NOMe)CH2- --> [(CH2 = C = NCOMe)MeO-] --> CH2 = C = NCOCH2- + MeOH, or a related Neber rearrangement. This investigation was aided by deuterium labelling, and product ion studies.