Visible light-promoted CO2 fixation with imines to synthesize diaryl \u03b1-amino acids

Xinyuan Fan,Mengyue Ma,Xu Gong,Patrick J Walsh,Rui Wang

doi:10.1038/s41467-018-07351-2

Abstract

Light-mediated transformations with CO2 have recently attracted great attention, with the focus on CO2 incorporation into C–C double and triple bonds, organohalides and amines. Herein is demonstrated visible light -mediated umpolung imine reactivity capable of engaging CO2 to afford α-amino acid derivatives. By employing benzophenone ketimine derivatives, CO2 fixation by hydrocarboxylation of C=N double bonds is achieved. Good to excellent yields of a broad range of α,α–disubstituted α-amino acid derivatives are obtained under mild conditions (rt, atmospheric pressure of CO2, visible light). A procedure that avoids tedious chromatographic purification and uses sustainable sunlight is developed to highlight the simplicity of this method.

Highlights

Light-mediated transformations with CO2 have recently attracted great attention, with the focus on CO2 incorporation into C–C double and triple bonds, organohalides and amines
At the outset of this work, we decided to limit ourselves to convenient conditions, so all reactions were conducted with atmospheric pressure of CO2 using a balloon at room temperature
Recent advances include photoredox catalyzed additions of CO2 to olefins, alkynes, aryl halides, alkyl halides and C–H functionalization of amines to afford a variety of useful carboxylic acids (Fig. 1)

Summary

Introduction

Light-mediated transformations with CO2 have recently attracted great attention, with the focus on CO2 incorporation into C–C double and triple bonds, organohalides and amines. Imines are known to participate in photoredox catalyzed processes, typically undergoing reduction followed by radical coupling reactions at the formerly carbonyl carbon[38,39,40,41,42,43] In contrast to this expected reactivity pattern, we[44], and Polyzos et al.[45], have recently discovered that under visible light catalysis, benzophenone-based ketimines undergo one electron reductions to generate carbanions that abstract protons from water (or deuterium from D2O) via an umpolung reactivity (Fig. 1d)[46]. Based on this reaction, we hypothesized that the nucleophilicity of this intermediate might be sufficient to engage CO2 providing α-amino acids. We report a visible light and sunlight mediated photoredox hydrocarboxylation of imines and the synthesis of α,α-disubstituted α-amino acids (Fig. 1e)

Methods

Results

Conclusion