o-Quinone Methides from 4-Allenylcyclobutenones:  Synthesis and Chemistry

Selected 4-allenylcyclobutenones ring expand to the corresponding o -quinone methides upon thermolysis in refluxing toluene or benzene. These reactive intermediates were not isolated but trapped to give stable products. The reaction has synthetic potential as a route to highly-substituted phenols, benzofurans, and aryl analogs of hexahydrocannabinol. In addition, a unique rearrangement involving a methyl migration from silicon to carbon of selected 4-[3,3-bis(trimethylsilyl)-1,2-propadienyl]cyclobutenones to give 1,2-benzoxasilols is described. Finally, data are presented that show rapid rotation around the alkylidene bond of o -quinone methides at 30 °C and that 2-(1-methylethenyl)phenols are in equilibrium with the corresponding o -quinone methides.