Recent advances in natural product synthesis by using intramolecular Diels-Alder reactions.

Simple indole alkaloids and those with a nonrearranged monoterpenoid unit

The development of efficient methods for the indole synthesis catalyzed by Cu(II) salts and its applications were investigated. Cu(OAc)2 has been proved to be the best catalyst for the synthesis of various 1-p-tolylsulfonyl or 1-methylsulfonylindoles, which have both electron-withdrawing and electron-donating groups on the aromatic ring and C2 position of indoles. For the primary aniline derivatives, Cu(OCOCF3)2 showed good activities, while Cu(OAc)2 was a good catalyst for the cyclization of secondary anilines. This methodology could be applied to the sequential cyclization reaction for the compounds which have the electrophilic part in the same molecule. By prior treatment with KH, the sequential cyclization was realized to provide the tricyclic ring systems, but it was limited to five- and six-membered rings for the second cyclization. Finally, formal and total synthesis of hippadine with the Cu(II)-promoted indole synthesis as the key step was accomplished.

Development of an Efficient Procedure for Indole Ring Synthesis from 2-Ethynylaniline Derivatives Catalyzed by Cu(II) Salts and Its Application to Natural Product Synthesis

Potharaju H. Rao

Papers

Alkaloids of Crinum pratense

Natural Occurrence of 11-O-Acetylambelline and 11-O-Acetyl-l ,2-β-epoxyambelline in Crinum latifolium: Immuno-regulant Alkaloids.