Experiments directed towards the synthesis of anthracyclinones. V. Double Claisen rearrangement of 1,4-Bis(allyloxy)anthraquinones

Abstract

The Claisen rearrangements of 1,4-bis(prop-2'-enyloxy)anthraquinone (4) and 1,4-bis(2'-chloroprop- 2'-enyloxy)anthraquinone (3) in o-dichlorobenzene have been examined. The former gives a low yield of 1,4-dihydroxy-2,3-bis(prop-2'-enyl)anthraquinone (22), and 1,4-dihydroxy-2-(prop-2'-eny1)- anthraquinone (5) as the major product. Also formed is 1-hydroxy-4-propanoyl-2-(prop-2'-enyl)- anthraquinone (6) which arises from an unprecedented rearrangement of one allyloxy group. 1,4-Bis(2?-chloroprop-2'-enyloxy)anthraquinone (3) gives mainly 2-(2'-chloroprop-2'-enyl)-4-(2'- chloroprop-2'-enyloxy)-1-hydroxyanthraquinone (11) and a variety of minor products which are dependent on the time of reaction. Treatment of compound (11) with ethanolic potassium hydroxide, followed by a further Claisen rearrangement, gives a high yield of the synthetically useful 4-(2'-chloro-prop-2'-enyl)-5-hydroxy-2-methyl-6,11-dihydroanthra[1,2-b]furan-6,11-dione (19).