ABC → ABCE/D Based Approaches to the Pentacyclic Ring System of the Vinca Alkaloids Using Intramolecular Hetero-[2+2]cycloaddition and Gold(I)-Catalyzed 6-endo-dig Cyclisation Protocols

Date

2015

Authors

Willis, Anthony C.
Banwell, Martin G.
White, Lorenzo V.

Journal Title

Journal ISSN

Volume Title

Publisher

Japan Institute of Heterocyclic Chemistry

Abstract

The angularly substituted tetrahydrocarbazole 13, which is readily obtained from cyclohexane-1,4-dione monoethylene ketal (6) using Fischer indole chemistry, has been converted into the isothiocyanate 16. Photolysis of this last compound affords, via an intramolecular hetero-[2+2]cycloaddition reaction, the pentacyclic "-thiolactam 17 that incorporates the ABCE ring substructure of natural products 1-3. Attempts to effect a two-carbon homologation of the four-membered ring within compound 17, and thereby establish the D-ring, failed. The azide 20, also obtained from compound 13, forms the cyclic imine 21 on thermolysis in refluxing toluene and the readily derived enamide 23 engages in a Au(I)-catalysed 6-endo-dig cyclisation reaction to give compound 24 embodying the ABCDE ring system of the title alkaloids.

Description

Keywords

tetrahydrocarbazole 13, isothiocyanate 16, Photolysis, ABCE ring substructure, two-carbon homologation, azide 20, compound 13

Citation

Source

HETEROCYCLES

Type

Journal article

Book Title

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