Metal-free Homocoupling of 2,2´-(Arylmethylene)-bis(3-hydroxy-5,5- dimethylcyclohex-2-enone) Mediated by N-methylhydroxylamine

The reaction of 5,5-dimethylcyclohexane-1,3-dione with an acyclic nitrone in DMF or acetone affords a 1:1 mixture of dimer 2,2´-(arylmethylene)-bis(3-hydroxy-5,5-dimethylcyclohex-2-enone) and tetramer 2,2','','''-(1,2- diarylethane-1,1,2,2-tetrayl)tetrakis(3-hydroxy-5,5-dimethyl-cyclohex-2-enone). This unprecedented type of metal-free homocoupling of two molecules of the dimer to furnish the tetramer is believed to proceed via an oxidation/reduction process involving N-methylhydroxylamine.