The reactivity, as electrogenerated bases, of chiral and achiral phenazine radical-anions, including application in asymmetric deprotonation

Abstract

Radical-anions, electrochemically generated in aprotic solvent from C(2) symmetric homochiral phenazine derivatives, act as chiral electrogenerated bases (EGBs) in the desymmetrisation by selective deprotonation of a prochiral epoxide (3,4-epoxy-2,3,4,5-tetrahydrothiophene-1,1-dioxide); the anion produced is trapped by mesitoic anhydride. The phenazines may be recovered in high yield by air oxidation. Enantiomeric excesses are modest (8-34%) but this is to our knowledge the first demonstration of such stereoselective electrochemically-initiated deprotonation. The reactivity of phenazine radical-anions as EGBs has also been explored by measurements of the rates of proton transfer; the prochiral epoxide was found to have a kinetic acidity similar to that of the methyltriphenylphosphonium cation.

Copper(I)‐Promoted Synthesis of Highly Substituted and Functionalized Tetrahydrothiophenes

“…The synthesis of functionalized THTs by substitution reactions of acyclic precursors with chlorine or bromine and/or acetoxy substituents already installed, using Na 2 S, NaSH, organic sulfides etc., is a common approach. [1b], [19b], However, such reactions are not suitable for the synthesis of β‐halo and α‐acetoxy THTs, or THTs containing other sensitive groups, due to the possibility of elimination, substitution, and other side reactions at these centres , , . On the other hand, radical cyclization is considered to be a mild and neutral method for the synthesis of carbo‐ and heterocycles, taking place under neutral reaction conditions, and with a high degree of functional group tolerance.…”

The X-ray Structures of 2- and 3-Sulfolene and Two Halogenated Derivatives

“…3) [15][16][17][18][19][20][21][22] and 2 (Fig. 4) [15,[23][24][25][26] that have been crystallographically characterised are shown with CSD reference codes, literature references and, as a measure of planarity, the sum of the five in-ring torsion angles. As compared to the structures of 1 and 2 which have all torsion angles zero, we can see that introducing a substituent has a range of effects on the degree of planarity from no effect (IPRNSO) to small (GAMKEK), moderate (BAHQEG, MIXYUN, XOJFUX, WASBOI) and fairly large (BAHQIK, VUFKIS, XUTVUF, VAGXAC).…”

Dispersion of Single-Walled Carbon Nanotubes with an Extended Diazapentacene Derivative

“…Under reductive conditions, new maxima evolve at 492, 622, and 698 nm, which we assign to the one-electron reduced species of 1. 32,33 Contrary to the reduction, the following changes occur during the oxidation: new maximum at 422 nm. None of the changes that relate to the different redox state seem, however, to match the changes seen in the femtosecond experiments.…”