Aerobic catalytic systems inspired by copper amine oxidases

Abstract

The goal of sustainable development has been accepted as a common policy in current society. In response to this challenge, the development of green processes which utilize environmentally benign oxidants, reduce chemical waste and handling costs, is highly desirable. Given the widespread importance of imines as pivotal synthetic intermediates and essential pharmacophores in numerous biologically active compounds, various catalytic methods allowing the aerobic oxidation of amines to imines have been developed. Recently, noticeable progress has arisen from the discovery of various quinone-based catalytic systems, inspired by copper amine oxidase enzymes (CuAOs), which are able to reproduce the selectivity of CuAOs for primary amines and even to expand the amine substrates scope. However, the need for synthesizing these catalysts prior use adversely affects the economics as well as the eco-friendly nature of the method. To surpass these drawbacks, the “second-order” biomimicry idea has been recently advanced to describe a system in which in situ modification of pre-catalyst components affords the active biomimetic catalyst. This minireview especially covers our recent contribution to the design of bioinspired quinone-based catalysts for the aerobic oxidation of amines to imines which has culminated in a dual bioinspired protocol as an example of “second-order” biomimicry.

A Comprehensive Review on Cu‐Catalysed Aerobic Oxidation of Amines to Imines

“…In 2019, our group demonstrated aerobic oxidation of primary benzylic amines to secondary imines under ambient circumstances using a Copper Amine Oxide (CAO) mimic [75] . As discussed above, imines are useful starting materials for a wide range of organic reactions, and they are also used as steps in the process of making acceptable compounds [7,80] They work well as pharmacophores in compounds with a physiological effect and as starting materials for making chiral amines and making them racemic [81] . Recently developed mild and environmentally friendly catalysts can be used to achieve the oxidative coupling of primary amines with aldehydes and ketones to give imines, but this conversion is constrained by factors like substrate range, enriched oxygen conditions, low turnover, utilization of costlier metals, the propensity to decompose, slower reaction times, and the requirement for elevated reaction temperatures [62,82–88] .…”

Innovative green oxidation of amines to imines under atmospheric oxygen

“…Many catalytic systems have been reported for the oxidation of amines to imines under pressurized oxygen or air; however, the use of pressurized oxygen (or air) is not a preferred reaction system because of the risk of explosion. 12–16 Therefore, this review is limited to address imine synthesis using the safer ambient pressure oxygen or air.…”

A biomimetic approach to aerobic oxidation of amines in water via a redox-active cacotheline organocatalyst

“…6 The designed transaminase catalysts have been shown to react with amines to give (ket)imine intermediates, which subsequently releases ortho -aminophenols for the crucial aerobic oxidation to ortho -iminoquinones as an active catalyst form (Scheme 1b). 7 Since low molecular weight transaminase catalysts are less soluble in water, the typical aerobic oxidation protocols of amines are performed in organic solvents. In 2014, the laboratories of Namboothiri and Doris achieved the aerobic oxidation of benzylamines to homo-coupled imines in the presence of gold nanoparticles on organic nanotubes (AuONT) and a gallacetophenone catalyst at ambient temperature in water.…”