Heterocyclic metamorphosis

I am always on the lookout for ways to convert one class of heterocycle into another. I think this is easier than building rings de novo. One can reasonably expect scaffold hopping approaches in fragment-based discovery to be greatly simplified with such metamorphosis-like pathways. Today I want to discuss one particular type of molecule that is as suited for this general idea, or is better than, any other heterocycle. I refer to indole, whose versatility is astounding. One recent sequence that attracted my attention is the one reported by Guan and colleagues. Here we have a Baeyer-Villiger-like oxidation of indole to give benzoxazinone nucleus.

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http://pubs.rsc.org/en/Content/ArticleLanding/2013/CC/c3cc44215b

This reaction was accomplished using oxone, which ruptured the indole moiety. There was another recent report, by Cui and co-workers, who accomplished a fairly similar ring-expansive goal, except they used indoles and amines under copper catalysis and ended up with arylquinazolinones (http://pubs.acs.org/doi/pdf/10.1021/acs.joc.5b00957 ).

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