James H. P. Utley

Radical-anions, electrochemically generated in aprotic solvent from C₂ 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.

1,6-Disubstituted phenazine derivatives for use as precursors to electrochemically generated bases have been synthesized from readily available starting materials. Reaction of 1,6-dihydroxyphenazine with 1,10-diododecane, 1,11-diiodo-3,6,9-trioxaundecane or (R,R)-(−)-1,2-bis(3-iodopropoxy)cyclohexane gave planar chiral phenazinophanes containing ether-linked bridges; molecular structures of all these compounds have been determined by X-ray crystallography. Substituted 1,6-diaminophenazines were prepared by palladium-mediated amination of 1,6-dichlorophenazine and acylation of 1,6-diaminophenazine followed by reduction. Reaction of 1,6-bis(alkylamino)phenazines with sebacoyl chloride gave planar chiral phenazinophanes containing amide-linked bridges.

The electrosynthesis of poly(p-xylylenes) (PPXs) and poly(p-phenylenevinylenes) (PPVs) by the direct and mediated cathodic reduction of (halomethyl)arenes is reviewed and, where appropriate, comparisons made with more conventional chemical routes. Attention is drawn to the advantages of mild (non-thermal) conditions and to the consequent toleration of a wide range of substituents in the (halomethyl)arene precursors. Copolymers are obtained by co-electrolyses and aprotic and aqueous conditions may be used. Several polymers that are inaccessible by the Wessling and related routes may be prepared electrochemically. The properties, including lifetimes, of the key quinodimethane (xylylene) intermediates have been examined by cyclic voltammetry and the results are consistent with a radical-chain mechanism for polymerisation, initiated by electrogenerated radical-anion. The physical properties of electrochemically derived polymers are comparable re molecular weight and photoelectrical properties to those prepared chemically.