Asian Journal of Organic Chemistry 2018-03-26

Cobalt/N, N', N''‐Trihydroxyisocyanuric Acid (THICA)‐Catalyzed Aerobic Oxidative Esterification and Amidation of Aldehydes

Biao-Lin Jiang; Bao-Hua Xu; Meng-Liang Wang; Zeng-Xi Li; Dian-Sheng Liu; Suo-Jiang Zhang

Index: 10.1002/ajoc.201800118

Full Text: HTML

Abstract

A system of Co(II)/N, N', N''‐trihydroxyisocyanuric acid (THICA)‐catalyzed aerobic oxidative esterification and amidation of aldehydes has been developed in this work. Preliminary insight of the mechanism indicates such an oxidative C−O/N cross‐coupling proceeded by masking aldehydes with alkoxyl/amino sources upon nucleophilic addition as the first step, thereby keeping the highly reactive formyl group thereof from undesired oxidation. Under this protocol, oxidative esterification and amidation of aldehydes represents two different cases imposed by the intrinsic nucleophilicity of alkanol and amine substrates. The former was attained in the presence of p‐CH3C6H4SO3H (TsOH) as co‐catalyst and using orthoformates as alkoxyl sources instead of alkanols to afford the transiency acetals efficiently. In contrast, coupling of more nucleophilic amines with aldehydes renders a readily occurred cross‐coupling in the absence of any co‐catalyst, but puts forward a new challenge owing to the potential inhibition of THICA upon nucleophilic substitution by amines. Consequently, only steric hindered amines were found tolerate in this catalytic system, while further condensation leading to imines were detected in the case of primary amines.