Emerging unconventional organic solvents for C-H bond and related functionalization reactions.

Congjun Yu,Mónica H Pérez-Temprano,Jesús Sanjosé-Orduna,Frederic W Patureau

doi:10.1039/c8cs00883c

Abstract

Solvent engineering is an increasingly essential topic in the chemical sciences. In this context, some recently appeared unconventional solvents have shown their large potential in the field of C-H bond functionalization reactions. This review aims not only at recognizing and classifying a short selection of these emerging solvents, in particular halogenated ones, but also at providing a medium term perspective of the possibilities they will offer for synthetic method development.

Highlights

Defining ‘‘unconventional organic solvent’’For the purpose of this tutorial review focused on direct C–H bond functionalization, an unconventional solvent may be defined as a seldom utilized organic solvent with reactivity supporting properties that go beyond solvents broadly considered as conventional
(4) So far, interestingly, the majority of these unconventional solvents arehalogenated
(5) More unconventional solvent enabled C–H bond functionalization reactivity can be expected in the coming years, as well as new privileged organic solvents

Summary

Introduction

Defining ‘‘unconventional organic solvent’’For the purpose of this tutorial review focused on direct C–H bond functionalization, an unconventional (or not yet conventional) solvent may be defined as a seldom utilized organic solvent with reactivity supporting properties that go beyond solvents broadly considered as conventional. Hexafluoroisopropanol (HFIP) is arguably the most popular oxo-halogenated unconventional solvent at the moment for C–H bond functionalization reactions, closely followed by trifluoroethanol (TFE).[2,3,4] of all the selected unconventional solvents covered in this review, HFIP and TFE already benefit from (somewhat) deeper mechanistic understanding. Their main features are a high polarity (for an organic solvent), combining both a hydrophobic as well as a hydrophilic side, and a mildly acidic OH group (pKa analogous to that of a phenol). This is combined with excellent single H-bond donor properties, a phenomenon enjoying growing consensus in the scientific community to explain its extra-ordinary reactivity enabling character.[2,3,4] Interestingly, this is associated with a very strong shielding effect at the oxygen atom, measured in 17O NMR

Objectives

Conclusion