Abstract:
Gentle heating of chloroallyloxyanthraquinones with sodium dithionite in dimethylformamide/water effects a rapid and controlled reductive Claisen rearrangement to give high yields of 2-chloroallylhydroxyanthra-quinones. One such product, 2-(2’-Chloroprop-2’-enyl)-4-(2”-chloroprop-2”-enyloxy)-1-hydroxyanthraquinone (71) prepared from readily available quinizarin (69) has been converted into (±)-4-demethoxydaunomycinone (4b) in 29% overall yield.
Ozonolyses of anthrafurans and 2,3-disubstituted anthraquinones has given some novel compounds, and their use in possible syntheses of 4-demethoxyanthracyclinones has been studied.
A preliminary investigation into the acid catalysed cyclisation of 4R,5R-dimethyl-2-[3-(2’-chloroprop-2’-enyl)-1-hydroxy-4-methoxy-9,10-dioxo-9,10-dihydroanthracen-2-yl]-1,3-dioxolane (119) to give optically active tetracyclic compounds has been carried out.