Distinctive reactivity of N-benzylidene-[1,1'-biphenyl]-2-amines under photoredox conditions.

Shrikant D Tambe,Kwan Hong Min,Naeem Iqbal,Eun Jin Cho

doi:10.3762/bjoc.16.114

Shrikant D Tambe, Kwan Hong Min + Show 2 more

Open Access

https://doi.org/10.3762/bjoc.16.114

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Journal: Beilstein journal of organic chemistry	Publication Date: Jun 18, 2020
Citations: 1	License type: CC BY 4.0

Affiliation: Chung-Ang University

Abstract

A simple photocatalytic method was developed for the synthesis of unsymmetrical 1,2-diamines by the unprecedented reductive coupling of N-benzylidene-[1,1'-biphenyl]-2-amines with an aliphatic amine. The presence of a phenyl substituent in the aniline moiety of the substrate was critical for the reactivity. The reaction proceeded via radical–radical cross-coupling of α-amino radicals generated by proton-coupled single-electron transfer in the presence of an Ir photocatalyst. On the other hand, symmetrical 1,2-diamines were selectively produced from the same starting materials by the judicious choice of the reaction conditions, showcasing the distinct reactivity of N-benzylidene-[1,1'-biphenyl]-2-amines. The developed method can be employed for the synthesis of various bulky vicinal diamines, which are potential ligands in stereoselective synthesis.

Highlights

The selective formation of distinct valuable compounds from the same starting material is a highly attractive divergent approach, though it represents significant synthetic challenges
In addition to the cross-coupled 1,2-diamines, we envisioned the generation of other valuable structural motifs via the careful control of the reaction conditions for the reaction of the biphenyl imine derivative N-benzylidene-[1,1'-biphenyl]-2amine
With the initial results in hand, we attempted the optimization of the reaction conditions to improve the yield of the 1,2-diamine product (Table 1)

Summary

Introduction

The selective formation of distinct valuable compounds from the same starting material is a highly attractive divergent approach, though it represents significant synthetic challenges. N-Benzylidenes can undergo facile single-electron reduction to generate α-amino radical intermediates, which can participate in diverse processes, depending upon the nature of the substrates and the reaction conditions (Scheme 1a). Reported excellent examples of the reductive umpolung homocoupling of imines and heterocoupling with α-amino radicals for the synthesis of symmetrical and unsymmetrical vicinal diamines (Scheme 1b) [23,26].

Results

Conclusion