Pyrazine chemistry. Part 12. Acid-catalysed rearrangements of cyclo-L-prolyl-L-[Na-(3,3-dimethylallyl)]tryptophyl

Abstract

Rearrangements of the title compound under the influence of trifluoroacetic and Lewis acids have been studied. Under no circumstances was deoxybrevianamide E formation observed. Amongst the rearrangement products isolated were two resulting from intramolecular Friedel–Crafts alkylations and two resulting from cleavage of the nitrogen–allyl bond. The chemical relationships between the rearrangement products has been explored. Lead tetra-acetate oxidation of the Friedel–Crafts product (6) introduced an acetate function at position 3 of the indole nucleus and acid catalysed a novel rearrangement of this, to the indolic nitrogen substituent, to give the epimeric aminol acetates (19) and hence the aminols (20); the latter were remarkably resistant to ring-opening under a variety of conditions.