That the 2, 3 adduct (2) does not arise by isomerization of the 1, 2 adduct (1) was shown by treating the pure nonconjugated ethylenimine adducts with ethylenimine in both ethanol and benzene; the starting adducts 1 were recovered unchanged. Resistance of adducts 1 to isomerization under reaction conditions rules out an allenic intermediate in the addition of ethylenimine to nonterminal acetylenic sulfones and sulfoxides, which yield only ...
