Co‐Catalyzed Metal‐Ligand Cooperative Approach for N‐alkylation of Amines and Synthesis of Quinolines via Dehydrogenative Alcohol Functionalization

Abstract

AbstractHerein we report a cobalt‐catalyzed sustainable approach for C−N cross‐coupling reaction between amines and alcohols. Using a well‐defined Co‐catalyst 1 a bearing 2‐(phenyldiazenyl)‐1,10‐phenanthroline ligand, various N‐alkylated amines were synthesized in good yields. 1 a efficiently alkylates diamines producing N, N′‐dialkylated amines in good yields and showed excellent chemoselectivity when oleyl alcohol and β‐citronellol, containing internal carbon‐carbon double bond were used as alkylating agents. 1 a is equally compatible with synthesizing N‐heterocycles via dehydrogenative coupling of amines and alcohols. 1H‐Indole was synthesized via an intramolecular dehydrogenative N‐alkylation reaction, and various substituted quinolines were synthesized by coupling of 2‐aminobenzyl alcohol and secondary alcohols. A few control reactions and spectroscopic experiments were conducted to illuminate the plausible reaction mechanism, indicating that the 1 a‐catalyzed N‐alkylation proceeds through the borrowing hydrogen pathway. The coordinated arylazo ligand participates actively throughout the reaction; the hydrogen eliminated during dehydrogenation of alcohols was set aside in the ligand backbone and subsequently gets transferred in the reductive amination step to imine intermediates yielding N‐alkylated amines. On the other hand, 1 a‐catalyzed quinoline synthesis proceeds through dehydrogenation followed by successive C−C and C−N coupling steps forming H2O2 as a by‐product under air.