Reactions of Ketene Acetals V The Reaction with p-Benzoquinone Dihalides

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Abstract
2- or 3-Halonaphthoquinones are known to react with ketene dialkyl acetals and to yield 1,3-dialkoxyanthraquinones2,3. Various p-benzoquinones on the other hand have given only 2-alkoxy-benzofurans2. 3-Chloro-5,7-dimethoxy-1,4-naphthoquinone (4) and 1,3,6,8-tetramethoxyanthraquinone (10), important intermediates for the synthesis of naturally occurring quinones, have now been obtained under analogous conditions using p-benzoquinone dihalides (trans-5,6-dihalo 2-cyclohexene 1,4-diones). Compound 4 does not appear to have been described but is readily converted to 3,5,7-trimethoxy-1,4-naphthoquinone (7) and regiospecifically3 to 1,3,6,8-tetramethoxyanthraquinone. Although the yields obtained in the reactions of ketene acetals with quinone dihalides are low, compounds 7 and 10 have only been prepared until now by tedious means involving a large number of steps4–8, or by the degradation of natural products9,10.