The Reactions of Monoalkylthio- or Monoarylthio-Substituted Cyclopropenium Salt with Nitrogen Nucleophiles: Formation of Polyfunctionally Substituted Pyrroles or Pyrazoles

Abstract

The reactions of monoalkylthio- or monoarylthio-substituted cyclopropenium salt (1) with a number of secondary amines were studied. The amines, such as N-methylaniline, yielded indenes, whereas N-alkyl- or N-arylbenzylamines gave 1-alkyl- or 1-aryl-2-phenylpyrroles in low-to-moderate yields, depending on the kinds of substituents of the amines and 1. The reaction with N-isopropylbenzylamine-α,α-d2 (i-PrNHCD2Ph) resulted in the formation of the 1-isopropyl-2,3,5-triphenylpyrrole-4-d, clearly indicating the intramolecular H-abstraction mechanism via vinylcarbene intermediates for the formation of pyrroles. The reaction of 1 with tosylhydrazones afforded the ring opend hydrazide, while with phenyl-, methyl-, and t-butylhydrazines gave 1,4,5-trisubstituted pyrazoles in small yields.