27: Some Natural and Unnatural Indoles (1990)

Liversidge Research Lecture delivered before the Royal Society of New South Wales, September 5th, 1990, at the University of New South Wales. Reproduced by permission of the Royal Society of New South Wales from J. Proc. Roy. N.S.W., 1990, 123, 1-13."New reactions of specially-activated indoles provide methods by which structures related to natural products can be produced. Various 4,6-dimethoxy-substituted indoles exhibit a variety of reactions, predominantly at C7, but others at C2 or C3 instead of C7. The general increase in nucleophilic character of these indoles allows the discovery of reactions which have not been observed for other indoles. These reactions include electrophilic substitution, and addition to aldehydes and ketones. Tri-indolyl macrocycles, pyrrolo[a]indoles, cyclopentano[b]indoles and indolocarbazoles can be produced. Furthermore, new ring-fused indoles can be prepared by intramolecular nitrone 1,3-dipolar cycloaddition reactions between N1 and C2 or N1 and C7. In the latter case, similar structures can be achieved by aldol-type or organometallic reactions. The use of N-aroylindoles enables some known pyrrolophenanthridone alkaloids and some of their unknown analogs to be synthesized effectively.