The complex anionic rearrangements of deprotonated α-oximino carbonyl derivatives in the gas phase

Abstract

α-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). (i) R1COC(NO–)R2 [graphic omitted] R1CO2–+ R2CN, and (ii) R1COC(NO–)CH2R [graphic omitted] –O(R1)CCCH2+ RNO(R = H or alkyl) 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 α-oximino ketones. The corresponding deprotonated α-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–→[(CH2CNCOMe)MeO–]→ CH2CNCOCH2–+ MeOH, or a related Neber rearrangement. This investigation was aided by deuterium labelling, and product ion studies.