Sonochemical Cycloadditions of o-Quinones. The Search for a Cation Radical Pathway.

Diels-Alder cycloadditions of an o-quinone monoketal with different furans, under argon, are considerably accelerated by ultrasonic irradiation. Moreover, these sonochemical reactions are regiospecific and proceed with a high diastereoselectivity. The results can be ascribed to the chemical role of ultrasounds which may favor a single electron transfer mechanism with respect to ionic or nonpolar pathways.