In 1993, Katayama et al.7 reported the intramolecular,
Lewis acid-promoted 1,2-addition of the azomethine
carbon of N-aminoindoline-derived hydrazones to a neighboring
carbonyl group in carbocyclization reactions.
Unfortunately, it was not possible to develop an intermolecular
version of this interesting reaction, presumably
due to the poor nucleophilicity of this type of hydrazone.
Trusting again in the higher reactivity exhibited by
formaldehyde N,N-dialkylhydrazones, we started studies
on the intermolecular 1,2-addition of these reagents to
carbonyl compounds.