One and two hydrogen atom migrations in the retro‐diels‐alder fragmentation of norbornene and bicyclo [2.2.2] octene derivatives under electron impact

Norbornene derivatives with one or two carbonyl‐containing substituents at positions 5 and 6 (anhydrides, esters, amides, cyclic ketones) undergo an electron impact induced rerro‐Diels‐Alder fragmentation accompanied by the migration of one hydrogen atom (RDA + H) giving rise to the [dienophile + H] + ions. Bicyclo[2.2.2]octene derivatives substituted at C(5) and C(6) by a ring with two carbonyl groups (anhydrides, imides, diketones) undergo an RDA fragmentation accompanied by the transfer of two hydrogen atoms (RDA + 2H). Bicyclo[2.2.2]octene 5,6‐diesters undergo both the RDA + H and RDA + 2H fragmentations, and the relative abundance of the resulting [dienophile + H] + and [dienophile + 2H] + ˙ ions is strongly affected by configuration.