o-Benzoquinone Methide: An Intermediate in the Gas-Phase Pyrolysis of Chroman

Article abstract of DOI:10.1021/jo00071a013

Gas-phase pyrolysis of chroman gives o-cresol, benzofuran, and styrene in a 4:2:1 ratio at 413 deg C.In the presence of 2-butene, a moderately stereospecific 4 + 2 reaction occurs with the likely intermediate, o-benzoquinone methide, 1.The addition of 2-butene increased the amount of reaction and decreased the extent of formation of benzofuran and styrene.Addition of hydrogen gas increased the amount of hydrodealkoxylation product, styrene, and gave more of its reduction product, ethylbenzene, at the expense of benzofuran.Only a slight increase in the amount of o-cresol was observed upon addition of hydrogen gas.No dehydrochroman was observed in the reactions, and pyrolysis of 4H- and 2H-benzopyran gave no o-cresol, but instead gave styrene, benzofuran, 1-indanone, and some chroman.