AgNTf2-Mediated Allylation with Allylsilanes at C3a-Position of Hexahydropyrroloindoles: Application to Total Syntheses of Amauromine Alkaloids.

A protocol for the allylation at the C3a-position of hexahydropyrroloindole using allylsilanes is developed. AgNTf2 proved to be an efficient activator of halopyrroloindoline substrates. This method is applicable to the introduction of various allyl groups including the reverse prenyl group. The utility of this reaction is demonstrated by total synthesis of amauromine alkaloids. Stepwise bromocyclizations of the bis-indolylmethyl diketopiperazine derivative and subsequent double reverse prenylation furnished (+)-novoamauromine and (-)-epiamauromine.