Solvent‐Dependent Regio‐ and Stereo­selective Oxidation of [2.2]Para­cyclophane‐Derived Phenols

Abstract

The structure of the products formed upon oxidation of 4‐hydroxy[2.2]paracyclophane and its derivatives with Cu(OH)Cl·TMEDA depends on the solvent used. In MeOH oxidation accompanied with nucleophilic attack of the solvent to furnish predominantly or exclusively ortho‐cyclohexadienones (o‐quinol methyl ethers) of (Rp*,Rp*) relative configuration. Oxidation carried out in CH2Cl2 results in regio‐ and stereoselective formation of para‐cyclohexadienone dimers {variously substituted 7,7′‐bis[2.2]paracyclophan‐4,4′(7H,7′H)‐diones} with (Sp*,Rc*,Rc*,Sp*) relative and (Rp,Sc,Rc,Sp) absolute configurations (two out of six possible diastereomers in each case), whereas oxidation of the enantiomerically pure phenol produced the respective single product. The dimeric cyclohexadienones can suffer aromatization to form the respective dimeric para‐biphenols under the action of KOH in EtOH.