Alkaloids from Croton species. Part V. Configuration of linearisine and circular dichroism of proaporphine-type alkaloids

From the signs and the positions of the circular dichroism bands of various proaporphine alkaloids their absolute configuration can be determined. The signs of the Cotton effects of the aromatic bands are not only dependent on the configuration but also on the type of substitution. The configuration of linearisine at the spiro-atom is shown to be (7aR) and the conformations of the enone and dienone chromophores of these alkaloids are deduced from the circular dichroism data.