Mannich bases as synthetic intermediates: Synthesis of 3- and 4-functionalized 2-pyrazolines

Abstract

The reaction of styryl ketonic Mannich bases 2a - c with phenylhydrazine leads to 3-functionalized 2-pyrazolines 4 or 6 depending on the reaction conditions. 3-[β-(Arylamino)ethyl]-2-pyrazolines 8a,b were obtained via transamination between the methiodide salt 7 and primary arylamines. Treatment of 1-(p-anisyl)-1,2,5-tri(N-piperidino)pentan-3-one (11) with phenylhydrazine affords the 3,4-difunctionalized 2-pyrazoline 12. The reactions of the keto bases 19 or 21 with hydrazines lead to 4-functionalized 2-pyrazolines 20 and 22, the N-Mannich bases 23 and 24 are obtained from 22a. The synthesis of 3-[β-(phenylthio)ethyl]-2-pyrazolines 28a,b has been achieved by treating 26 or 27 with phenylhydrazine. © 2007 Verlag der Zeitschrift für Naturforschung.