Diels-Alder reactions of 2′-hydroxychalcones with ortho-benzoquino-dimethane:: A new synthesis of 3-aryl-2-naphthyl 2-hydroxyphenyl ketones

Diels-Alder reactions of the 2'-hydroxychalcones 1a-e with ortho-benzoquinodimethane (3) yielded the 3-aryl-1,2,3,4-tetrahydro-2-naphthyl 2-hydroxyphenyl ketones 4a-e in good yields. The dehydrogenation of the cycloadducts 4a-e to 3-aryl-2-naphthyl 2-hydroxyphenyl ketones 5a-e was studied. Good results were obtained when DDQ was used as oxidant and microwave irradiation as energy source. Several benzoxanthone derivatives were also obtained as minor products. Structures of all new compounds were established by extensive NMR studies.