An improved synthesis of α,β-unsaturated enal or enone dimethylhydrazones

Dimethylhydrazones of β-dimethylaminomethyl-substituted carbonyl compounds treated with methyl iodide underwent chemoselective methylation at the trialkylamino group. Subsequent treatment of the resulting iodomethylates with bases yielded dimethylhydrazones of α,β-unsaturated enals or enones in high yields. For unsaturated hydrazones, which were stable to bases, the optimal cleaving agent was an aqueous solution of KOH; if labile trimethylsilyl groups were present in the substrate, the best results were obtained with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU).