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■ Regiocontrolled Total Syntheses of the Tropoloisoquinoline Alkalnoids Imerubrine and Grandirubrine

Martin G. Banwell,* Ernest Hamel, Neil K. Ireland, and Maureen F. Mackay

*School of Chemistry, The University of Melbourne, Parkville, Victoria 3052, Australia

Abstract

The previously reported dihydroazafluoranthene (8) has been converted, over a number of steps, into the σ-homo-o-benzoquinone monoacetal (5). The structure of compound (5) was established by X-ray crystallographic methods and treatment of this material with trifluoroacetic acid resulted in formation of the tropoloisoquinoline alkaloid imerubrine (1). Alternatively, acetal (5) could be hydrolysed to the corresponding diketone (6) which proved to be unstable and isomerised to grandirubrine (2) on heating. Both tropoloisoquinolines (1) and (2) were tested for antitubulin activity, and weak inhibition of polymerisation was observed only with the former compound.