Thermal reaction of diastereomeric benzocyclobutenols. Evidence for reversible opening of 1,2-dihydrobenzocyclobutenols to hydroxy-o-xylylenes

Thermolysis of 1,2-dihydrobenzocyclobutenols 2a,b or 3a–c without solvent at 120 °C gave a 1∶1 mixture of 2a–c and 3a–c together with 3-hydroxy-2,2-dimethyl-1-(o-methylphenyl)alkan-1-ones 1a–c and o-methylisobutyrophenone 5. Thermolysis of 2a or 3a under the same conditions but at 150 °C gave only 5. Thermolysis of 2c or 3c in benzene-d6 at 120 °C resulted in clean interconversion between 2c and 3c. Thermolysis of 1,2-dihydrobenzocyclobutenols 2d–f or 3d–f without solvent at 150 °C gave a mixture of 2d–f and 3d–f together with 3-acetoxy-2,2-dimethyl-1-(o-methylphenyl)alkan-1-ones 1d–f and benzyl ketones 9a–c.