Unexpected cleavage of the N–N bond in the reactions of 3-pyrazolidinone-1-azomethine imines with HCN

Abstract

Treatment of (1 Z,4 R ∗,5 R ∗)-1-arylmethylidene-4-benzamido-5-phenylpyrazolidin-3-one 1-azomethine imines 4a– d with potassium cyanide in the presence of acetic acid resulted in addition of HCN to the exocyclic C N double bond followed by β-eliminative N–N single bond cleavage (ring opening) to give the N-[(1 R ∗,2 R ∗)-3-amino-2-benzamido-3-oxo-1-phenylpropyl]benzimidoyl cyanides 6a– d in 28–85% yields. Reaction of dipole 4e with HCN furnished stable intermediate, (1′ S ∗,4 R ∗,5 R ∗)-4-benzamido-1-[cyano(mesityl)methyl]-5-phenylpyrazolidin-3-one ( 5e), in 76% yield. The structure of compound 6c was determined by X-ray diffraction.