Synthesis of β-tosylethylhydrazine and its use in preparation of N-protected pyrazoles and 5-aminopyrazoles

David M. Dastrup; Amy H. Yap; Steven M. Weinreb; James R. Henry; Andrew J. Lechleiter

doi:10.1016/j.tet.2003.11.046

Synthesis of β-tosylethylhydrazine and its use in preparation of N-protected pyrazoles and 5-aminopyrazoles

David M. Dastrup, Amy H. Yap, Steven M. Weinreb, James R. Henry, Andrew J. Lechleiter

Source

Tetrahedron > 2004 > 60 > 4 > 901-906

Abstract

β-Tosylethylhydrazine (6) can be prepared efficiently in one step from commercially available p-tolyl vinyl sulfone (7) and hydrazine hydrate. This hydrazine reacts with both 1,3-diketones and conjugated ynones in glacial acetic acid to provide a variety of N-tosylethyl-protected (TSE) pyrazoles in good yields. The TSE group can be removed from the pyrazoles using potassium t-butoxide in THF at -30 ^o C-rt. In addition, hydrazine 6 condenses with β-ketonitriles and β-aminoacrylonitriles to afford 5-aminopyrazoles, which can be deprotected by brief treatment with NaOEt in EtOH/DMSO at 45 ^o C.