Concise Total Synthesis of (±)-cis-Trikentrin A and (±)-Herbindole A via Intermolecular Indole Aryne Cycloaddition

An efficient nine-step total synthesis of the annulated indole natural products (+/-)-cis-trikentrin A and (+/-)-herbindole A was accomplished via an intermolecular Diels-Alder cycloaddition using our recently developed indole aryne (indolyne) methodology as the key step. This strategy provides rapid access into the trikentrins and the related herbindoles and represents the first application of this methodology to natural products total synthesis. The required 6,7-indolyne precursor was readily constructed by means of the Bartoli indole synthesis with substituted nitrobenzenes and vinyl magnesium bromide.