Octacycles and Nonacycles from 3-Hydroxy-2,2'-bisindole.

3-Hydroxy-2,2'-bisindole undergoes acid- and base-mediated dimerization-skeletal rearrangement processes, generating polyheterocyclic ring systems containing up to nine rings. The mechanistic rationale for these reactions is provided, which infers some overlap with the previously reported reactivity of 3',3″-dihydroxytetraindole under analogous reaction conditions.

Synthetic Studies toward Bisindigotin: Polyheteroaromatic Scaffolds via Skeletal Rearrangements of a Diacetoxytetraindole.

The deacetylation of a diacetoxytetraindole formed the basis of a first-generation synthetic route toward the alkaloid bisindigotin. However, this conceptually straightforward plan led to unexpected results. Acid-mediated hydrolysis initiated skeletal rearrangement processes that resulted in the formation of two novel heteroaromatic scaffolds, both of which contain nine rings. Upon treating the same diacetoxytetraindole with base followed by a silica-mediated autoxidation, a distinct cascade process occurred, generating another novel scaffold also comprising nine rings. A mechanistic rationale for these observations is provided.