Synthetic reactions driven by electron-donor–acceptor (EDA) complexes

Abstract

The reversible, weak ground-state aggregate formed by dipole–dipole interactions between an electron donor and an electron acceptor is referred to as an electron-donor–acceptor (EDA) complex. Generally, upon light irradiation, the EDA complex turns into the excited state, causing an electron transfer to give radicals and to initiate subsequent reactions. Besides light as an external energy source, reactions involving the participation of EDA complexes are mild, obviating transition metal catalysts or photosensitizers in the majority of cases and are in line with the theme of green chemistry. This review discusses the synthetic reactions concerned with EDA complexes as well as the mechanisms that have been shown over the past five years.

Visible Light‐induced Functionalization of C−H Bonds: Opening of New Avenues in Organic Synthesis

“…[71] Initially, the photoredox properties of the Ni-complex were examined by carrying out various experiments like luminescence experiments, cyclic voltammetry experiments that suggested Ni(II)À TPP to exhibit dual redox properties i. e., it can undergo reductive as well as oxidative quenching. Using this as a photocatalyst, the annulation reaction was carried out using N,N-dimethylaniline (80), and maleimide (81) under oxygen atmosphere to provide tetrahydroquinoline derivative (82) (Scheme 31).…”

“…This photoactive transient species involves the association of electron-rich (donor) and electron-deficient substrate (acceptor). [79,80] Although these substrates do not absorb the light individually, the EDA complex with these substrates absorbs light. The key feature of this milder synthetic methodology is that it does not rely on any exogeneous photocatalyst.…”

“…In 2018, the Sunden group reported a photochemical EDAcomplex promoted oxidative annulation reaction to achieve the cis-fused tetrahydroquinolines derivatives (82) (Scheme 40). [82] This reaction is driven by the addition of α-amino radical generated from the dialkylanilines (80) to maleimides (81). Authors proposed that atmospheric oxygen was served as an external oxidant and concentration of EDA complex facilitated the reaction turnover.…”

“…The reaction of dialkylanilines (80) with the maleimides initiated the radical reaction by forming EDA-complex that eventually transformed into a α-aminoalkyl radical (LI) and the maleimide radical (LII) via proton transfer under light irradiation (Figure 19). Attack of LI on maleimide generated the radical (LIII) which carried out rapid cyclization, forming intermediate LIV.…”

Intramolecular photochemical [2 + 1]-cycloadditions of nucleophilic siloxy carbenes

“…In recent years, more economical and sustainable catalyst-free methods for chemical synthesis have emerged employing visible light irradiation to generate reactive intermediates in the absence of photocatalysts or photosensitisers. 8 Within this context, catalyst-free [2 + 1]-photocycloadditions of olefins with carbenes generated from diazo compounds have been developed. 9 For example, in 2018 Davies first demonstrated that electrophilic carbenes generated photochemically from diazoacetates underwent [2 + 1]-cycloaddition with unsaturated carbocycles and heterocycles ( Fig.…”