Experiments Directed Towards the Synthesis of Anthracyclinones. XXII. Novel Cyclopropanation Reactions

Iodine/potassium carbonate induced cyclization of hydroxyanthraquinones with ortho-allyl side chains gives iodomethyldihydrofuran anthraquinones which undergo a novel cyclopropanation reaction on treatment with methanolic potassium hydroxide, e.g. (9) gives (12) in 77% yield, and (10) gives (13) in 62% yield. The scope of the reaction is explored and a number of by-products are identified and, where possible, their formation is rationalized.