Electrosynthesis 2.0 in 1,1,1,3,3,3‐Hexafluoroisopropanol/Amine Mixtures

Abstract

The intention of this review is to highlight the innovative electrolyte combination of 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) with tertiary nitrogen bases in electro-organic synthesis. This easy applicable and promising mixture is not yet well established in electro-organic synthesis, but expands the various possibilities in the latter. Combinations of fluorinated alcohols with nitrogen bases form highly conductive electrolyte systems, which can be evaporated completely. Consequently, no additional supporting electrolyte is required and work-up procedures are tremendously simplified. With this electrolyte mixture carbon-carbon homo-and cross-coupling reactions of arenes and phenols have been established with substrates that have not been previously susceptible to the anodic dehydrogenative coupling reaction. The intermediate installation of highly fluorinated alkoxy moieties can be exploited for subsequent conversions as well as various benzylic functionalization, including asymmetric transformations. These transformations show unique selectivity and functional group tolerance making them highly applicable to the synthesis of sophisticated structural motifs, including natural products.

Reproducibility in Electroorganic Synthesis—Myths and Misunderstandings

“…This is simply not accurate,a se ach parameter influences each other,m ost dominantly the interaction between electrodes and the electrolyte.T he redox performance of the cell is precisely adjusted by the choice of electrode material plus the composition of the electrolyte, which consists of solvent and as upporting electrolyte.T he latter can be as alt, acid, or base. [17] This liaison enables the user to shift the electrochemical window quite extensively.…”

Metal‐Free Electrochemical Synthesis of Sulfonamides Directly from (Hetero)arenes, SO2, and Amines

“…[43] However, complexes of triethylamine or DIPEA with SO 2 are relatively unstable. [31,44] Furthermore, the presence of HFIP could weaken the S À N interaction, so that DIPEA takes the role as base in this reaction also leading to deprotonation of HFIP, which is considered as additional supporting electrolyte [45] and protonation probably also minimizes competitive oxidation of DIPEA. In general, sterically hindered amine substrates with weaker S À N interaction, such as dibenzylamine or 2,2,6,6-tetramethylpiperidine, did not perform well in this reaction.…”

Developments in the Dehydrogenative Electrochemical Synthesis of 3,3′,5,5′‐Tetramethyl‐2,2′‐biphenol

“…Therefore, it became clear that fluorinated media, in particular, HFIP, are essential for the effective electrochemical dehydrogenative coupling of phenols. However, since HFIP can be recovered easily by distillation, there is only a minor economic impact [52] …”