Total Synthesis of (±)-Herbindole B and (±)-cis-Trikentrin B

Herbindole B and cis-trikentrin B are naturally occurring indoles having the unusual and synthetically challenging pattern of carbon substitution at the 4−7 and 5−7 positions, respectively, with no substitution at the 1−3 positions. The total syntheses of these polyalkylated indoles have been achieved in 19 and 12 steps, respectively. The synthesis of herbindole B relies on two iterations of a quinine monoimine Diels−Alder reaction, while cis-trikentrin B uses a single cycloaddition of a suitable quinone monoimine. Indolization of the adducts provides suitably substituted benzopyrrole nuclei for elaboration to the natural products.