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.

Oxidation of 4-hydroxy[2.2]paracyclophane and its derivatives with Cu(OH)Cl·TMEDA in MeOH leads to ortho-cyclohexadienones of (Rp*,Rp*) relative configuration, whereas in CH₂Cl₂ regio- and stereoselective oxidative coupling occurs to produce variously substituted 7,7′-bis[2.2]paracyclophan-4,4′(7H,7′H)-diones with (Sp*,Rc*,Rc*,Sp*) and (Rp,Sc,Rc,Sp) relative configurations.

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