Use of Acylhydrazones as Electrophiles in Mannich-Type Reactions, β-Lactam, Pyrazolidinone, and Pyrazolone Synthesis

In the presence of a catalytic amount of scandium triflate [Sc(OTf)₃], 4-trifluoromethylbenzoylhydrazones reacted with silyl enolates to afford the corresponding adducts, β-N′-acylhydrazinocarbonyl compounds, in high yields. Reductive cleavage of the nitrogen-nitrogen bond of the hydrazino compounds was performed using Raney Ni under H₂ atmosphere, to give β-aminocarbonyl compounds. The two-step process is regarded as a novel Mannich-type reaction using acylhydrazones as electrophiles. Moreover, the hydrazino compounds were also successfully converted to β-lactam, pyrazolidinone, and pyrazolone derivatives.

acylhydrazone - rare earth triflate - Mannich reaction - β-lactam - pyrazolidinone - Lewis acid catalysis