Well-documented applications of p -phenylenediamine in the synthesis of heterocycles and heterocrown ethers

Abstract

(A) Synthesis of Quinoxalines: Quinoxalines are an important class of heterocyclic compounds, some of which are found to be useful as fluorophores, dyes, and antibiotics. p-Phenylenediamine I reacted with pyridine-2- carboxaldehyde II in methanol at room temperature to produce an imine III which upon treatment with copper(II) salts produced the highly fluorescent novel quinoxaline derivative IV.6 (figure presented) (B) Synthesis of Bis-N-Heterocyclic Carbene (NHC) Precursors: p-Penylenediamine was used as a spacer for the synthesis of a bis-Nheterocyclic carbene (NHC) precursor of a homo-bimetallic ruthenium-type catalyst. 7 This catalyst was used for the dimer ring-closing metathesis. (figure presented) (C) Synthesis of Bis-Quinolone Derivatives: Zewge et al. developed a general and high-yielding synthetic strategy for the synthesis of bis-quinolones using p-phenylenediamine as a key material. 8 The first step was the formation of enamine I by the reaction between p-phenylenediamine and dimethyl acetylenedicarboxylate (DMAD) in alcoholic solvents. Finally, the enamine was cyclized to the corresponding bis-quinolones II using Eatons reagent as an efficient cyclizing agent. (figure presented) (D) Synthesis of Pentasubstituted Pyrroles: Binder and Kirsch reported that both amine groups of p-phenylenediamine could be converted simultaneously into the corresponding pentasubstituted pyrrole by using a combination of propargyl vinyl ether, silver(I) and silver(II) salt in dichloromethane through a convenient one-pot process.9 Basically this is an example of a one-pot, three-step cascade reaction: first the silver(I)-catalyzed propargyl Claisen rearrangement, followed by amine condensation and finally gold(I)-catalyzed 5-exo-dig heterocyclization. (figure presented) (E) Synthesis of Polysubstituted Aromatic Pyrroles: Scheidt and co-workers reported that one amine group of the p-phenylenediamine could selectively be converted into the 2,3,5-trisubstituted pyrrole by following a newly developed one-pot synthetic strategy. 10 The reaction between benzoyltrimethylsilane, chalcone, and p-phenylenediamine under the newly developed conditions produced the desired trisubstituted pyrrole. (figure presented) (F) Synthesis of 6-Aminoquinazolines: Chilin et al. introduced a new synthetic pathway to quinazolines. They were successful enough to convert selectively one amino group of p-phenylenediamine into the corresponding pyrimidine ring furnishing 6-aminoquinazoline as the only product. 11 (figure presented) (G) Synthesis of Crownophanes: Sibert et al. incorporated the electrochemically active p-phenylenediamine unit into the body of crown ether and produced a macrocyclic hybrid crown/cyclophane structure called as Wursters crownophanes. During the synthesis of this type of crownophanes, Sibert et al. isolated two types of crownophanes, one smaller (I) and one larger (II). 4 (figure presented) © Georg Thieme Verlag Stuttgart New York.