Trapping of o-quinodimethane with p-quinones: synthesis of tetrahydro-1,4-anthracenediones

Previous work from our laboratory has been concerned with investigating the photochemical reactivity of the tetrahydro-1,4-napthalenedione system, both in solution and the solid state. The results obtained prompted us to extend our studies to the analogous tetrahydro-1,4-anthracenedione system. The most direct method of synthesis of the desired compounds is through Diels–Alder addition of o-quinodimethane to p-quinones. Because of the ease with which the adducts would be expected to undergo bis-enolization to the corresponding hydroquinones, their preparation requires mild, neutral conditions. After much experimentation, success was achieved using the Durst–Charlton sulfur dioxide extrusion method for generating o-quinodimethane from 3,6-dihydro-1,2-oxathiin-2-oxide. Insitu trapping using p-benzoquinone and other substituted p-quinones afforded the desired adducts in reasonable yields. In the case of duroquinone and 2,3-dimethyl-1,4-naphthalenedione, fluoride ion-catalyzed generation of o-quinodimethane from [o-[α-(trimethylsilyl)methyl]benzyl]trimethylammonium bromide by the method of Ito also gave acceptable results; however, the bis-enolizable adducts were not stable under these eaction conditions.