In 1950, Horowitz and Geissman reported the first example of the 2-aza-Cope rearrangement, a surprising result in a failed attempt to synthesize an amino alcohol.[2]  This discovery identified the basic mechanism of the rearrangement, as the product was most likely produced through a nitrogen analog of the Cope rearrangement.  Treatment of an allylbenzylamine (A) with formic acid and formaldehyde leads to an amino alcohol (B).  The amino alcohol converts to an imine under addition of acid (C), which undergoes the cationic 2-aza-Cope rearrangement (D).  Water hydrolyses the iminium ion to an amine (E).  Treating this starting material with only formaldehyde showed that alkylation of the amine group occurred after the cationic 2-aza-Cope rearrangement, a testament to the quick facility of the rearrangement.[2]