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Communication | Special issue | Vol 28, No. 1, 1989, pp.137-142
Published online, 1st January, 1970
DOI: 10.3987/COM-88-S62
Chiral Economy with Respect to Rotational Isomerism: Rational Synthesis of Hamatine and (Optionally) Ancistrocladine from Joint Helical Precursors

Gerhard Bringmann* and Johannes R. Jansen

*Institut für Organische Chemie, Universität Wurzburg, Am Hubland, D-97074 Wurzburg, Germany

Abstract

Unlike the target alkaloids 1a and 1b, which are configurationally stable at the biaryl linkage, the helicene-like distorted cyclic precursors 2 and 7 show dramatically lowered rotational thresholds: they equilibrate at room temperature, already. In contrast to the lactones 2a/b, however, the cyclic ethers 7a and 7b interconvert slowly enough to be separated conveniently, on a preparative scale. Ring opening of the desired helimer (e.g. 7b) and re-equilibration/re-separation of the rest allows the transformation of practically the whole synthetic material, optionally into 1b or 1a - practising “axially chiral economy”.