Nucleophilic displacements of N-aryl and heteroaryl groups. Part 3. Pyrylium-mediated synthesis of unsymmetrical diarylamines from anilines

Abstract

2-Ethoxycarbonyl-4,6-diphenylpyrylium salts (1 ) reacted with various ring-substituted anilines to give the corresponding pyridinium salts (2) (average yield 90%) ; these were hydrolysed to the pyridinium betaines (3) (75%) and treated with thionyl chloride followed by an aniline to give the amides (4) (70%). Refluxing in toluene with sodium hydride for 12 h transfers intramolecularly the 1 -aryl group of the pyridinium salt (4) to the nitrogen of the amide. Aqueous work-up cleaves (6) and the diarylamine is purified by sublimation (60%) (overall yield ca. 30%).

The Chapman rearrangement in a continuous-flow microreactor

“…What is more, only a limited substrate scope can be effected via cross-coupling reactions. 17 Therefore, the Chapman rearrangement is the method of choice in numerous synthetic routes of practical relevance.…”