SYNTHESIS OF PARA-CHLOROPHENOLS (AND PARA-CHLORONAPHTHOLS) FROM THE THERMAL REARRANGEMENT OF 4-CHLOROCYCLOBUTENONES

A systematic study of the reaction of 4-hydroxycyclobutenones with thionyl chloride is reported. A useful model evolves from this study which allows the prediction of the site of chlorination for unsymmetrical examples. The chlorination is envisaged to involve the corresponding homoaromatic carbocation, and the site of chlorination takes place preferentially at the position substituted with the greater cation-stabilizing substituent. Specifically, this follows the general order of allyl > benzyl > alkyl > propargyl. The 4-chlorocyclobutenones prepared in this study were shown to be useful synthetic precursors to highly substituted chlorophenols and chloronaphthols.