Co-Catalyzed Metal-Ligand Cooperative Approach for N-alkylation of Amines and Synthesis of Quinolines via Dehydrogenative Alcohol Functionalization |
| |
Authors: | Sucheta Mondal Subhasree Pal Subhankar Khanra Santana Chakraborty Dr. Nanda D. Paul |
| |
Affiliation: | Department of Chemistry, Indian Institute of Engineering Science and Technology, Shibpur Botanic Garden, Howrah, 711103 India |
| |
Abstract: | Herein 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. |
| |
Keywords: | Borrowing hydrogen Cobalt(II) complex Metal-ligand cooperativity N-alkylation Quinoline synthesis |
|
|