A solvent-directed stereoselective and electrocatalytic synthesis of diisoeugenol

Abstract

A stereoselective and electrocatalytic coupling reaction of isoeugenol has been reported for the first time in a 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP)/boron-doped diamond (BDD) electrode system. This particular C-C bond formation and diastereoselectivity is driven by a solvate interaction between the radical species and another isoeugenol molecule. Due to an electrocatalytic cycle, only understoichiometric amounts of charge are necessary. Since electric current is directly employed as the oxidant, the reaction is metal and reagent-free. In addition, the electrolysis can be conducted in a very simple undivided beaker-type cell under constant current conditions. Therefore, the protocol is easy to use, suitable for scale-up, and inherently safe.

Hexafluoro‐2‐Propanol‐Promoted Electro‐Oxidative [3+2] Annulation of 1,3‐Dicarbonyl Compounds and Alkenes

“…Lithium perchlorate and n Bu 4 NPF 6 showed the decreased reaction efficiency (entry 8–9). It was worth mentioning that both removing the HFIP and replacing the HFIP with other protic solvent such as methanol or water prevented the transformation (entry 10–11), manifesting HFIP might serve as a specific “stabilizer” to a large extent . Similarly, the poor yields were obtained when using the HFIP as the single solvent or using other common solvents such as DMF or DCE instead of CH 3 CN (entry 12–13).…”

Electrons and Holes as Catalysts in Organic Electrosynthesis

“…The constant current anodic oxidation of isoeugenol 16 using a boron doped diamond (BDD) electrode and HFIP as the solvent affords diisoeugenol 19 in a 57 % yield . As in the case of the electrochemically catalyzed NKR shown in Scheme , HFIP plays a critical role in stabilizing radicals and furthermore, in promoting a diastereoselective process leading to 19 .…”

“…The Faradaic efficiency with values > 100 % has previously been used for characterizing electrochemically catalyzed redoxneutral reactions (see refs. [2][3][4][5]). However, the use of the Faradaic efficiency implies a theoretical number of electrons required per conversion of a molecule, which is in conflict with the electroneutrality of electrochemically catalyzed reactions.…”

“…The constant current anodic oxidation of isoeugenol 16 using a boron doped diamond (BDD) electrode and HFIP as the solvent affords diisoeugenol 19 in a 57 % yield. [5] As in the case of the electrochemically catalyzed NKR shown in Scheme 8, HFIP plays a critical role in stabilizing radicals and furthermore, in promoting a diastereoselective process leading to 19. The solvent is said to pre-organize the reacting partners in a socalled "HFIP solvate cage" consisting of an aromatic donoracceptor interaction between the electron rich ring of isoeugenol (16) and the electron deficient ring in radical 17 c. Such preorganization is believed to be responsible for their diaste-reoselective coupling to afford radical 18.…”

“…In these cases, an electrochemical step catalyzes an overall redox-neutral chemical reaction, which is why these scenarios are referred to as "electrocatalyzed" [2][3][4][5] or "electrochemically catalyzed". [6][7][8][9] While the underlying principles were originally described in the context of inorganic and organometallic chemistry, [10,11] they were later successfully applied to organic reactions such as cycloadditions, [3,5] nucleophilic aromatic substitutions, [12] olefin isomerizations [13] and a number of molecular rearrangements. [14,15] The intent of this review is to discuss the fundamental aspects of such electrochemically catalyzed reactions, and to show the applications in organic electrochemistry from the early discoveries to the most recent developments.…”