Stereospecific Thermal Isomerization of 2,2-Dimethylbenzocyclobutenols to 2-Isopropenylphenyl Alcohols

Abstract

Thermolysis of the 1-alkyl-2,2-dimethylbenzocyclobutenol 3 at 160 degrees C gave the 2-isopropenylphenyl alcohol 8 through an (E)-dienol intermediate by a 1,5-sigmatropic hydrogen shift from the isopropylidene methyl group to the carbon bearing hydroxy group. In the thermolysis of each of the diastereomeric 2, 2-dimethylbenzocyclobutenols 6 and 7 which have a hydroxy group on the beta-carbon of the quaternary C(1)-alkyl substituent, the isomerization to the 2-isopropenylphenyl alcohols 10 and 11 took place stereospecifically through a twisted (E)-dienol intermediate. The configuration of the newly formed chiral center in 10 and 11 was the same as that of the ring carbon bearing hydroxy group in the starting 6 and 7.