Catalyst- and additive-free [3 + 3] cyclization–aromatization of β,γ-dioxobutanoate with amines for synthesis of p-aminophenols

Abstract

Cyclization–aromatization of enamines is a powerful method for the establishment of aza-aromatic cycles. We report herein the development of a simple and practical [3 + 3] aldol cyclization–aromatization of β,γ-dioxobutanoate with amines for the synthesis of p-aminophenols. Reactions with primary, secondary, benzyl and aryl amines all proceeded smoothly under mild reaction conditions, without catalysts and additives. Sensitive functionalities and heterocycles such as alcohol, ether, halogen, carboxylic acid, alkyne, pyridine, imidazole and free (N–H) indole, which could interfere with metal-, or acid-mediated processes, were well tolerated. The high degree of compatibility and practicability of this method is demonstrated by the late-stage cyclization–aromatization of structurally complex drug molecules.