Kvsn. Murty et al., SYNTHESIS OF UNNATURAL HYDROXYANTHRAQUINONES - EXPERIMENTS TOWARDS TOTAL SYNTHESIS OF PRADIMICINONE, Indian journal of chemistry. Sect. B: organic chemistry, including medical chemistry, 36(2), 1997, pp. 126-132
The phthalide sulfone 5 has been prepared from readily available ester
6 in four steps on multigram scales. This has been utilized in anioni
c [4 + 2] cycloaddition with a few cyclohexenones (12-14) to obtain an
thraquinones (18-26) in good yields, compound 21 being a potential int
ermediate for pradimicinone 1.