STUDIES ON QUINONES .24. REARRANGEMENT OF DIELS-ALDER ADDUCTS OF ACTIVATED QUINONES UNDER ACIDIC CONDITIONS

The Diets-Alder adducts 5, 19, 9, 10, 8, 11, of benzoquinones bearing activating groups (COCH3, COCH=CHPh, CO2Me, NO2, CHO, CN) by treatment with 1.3 N hydrochloric acid are initially converted into the dihydrobenzofurans 7, 22, the corresponding alcohols 12, 13 or the arylcrotonaldehydes 14, 15, respectively. By treatment with 8.5 N hydrochloric acid, adducts 8-10 are converted directly into the corresponding dihydrobenzofurans. In the presence of silica gel, adduct 19 is partially converted into the benzocyclooctatriene derivative 21. The alcohol 26, formed by hydrolysis of adduct 25, rearranges to the benzodifuran derivatives 28 and 29 in the presence of silica gel and ethanol or methanol, respectively.