Unprecedented Vilsmeier formylation: expedient syntheses of the cruciferous phytoalexins sinalexin and brassilexin and discovery of a new heteroaromatic ring system

reaction: see text]. A very concise first synthesis of sinalexin was achieved by regioselective formylation of 1-methoxyindoline-2-thione under Vilsmeier conditions followed by unprecedented ammonia workup. Similar formylation of indoline-2-thione yielded brassilexin and a novel pentacyclic heteroaromatic compound resulting from condensation of the Vilsmeier adduct of indoline-2-thione. Both sinalexin and brassilexin displayed strong antifungal activity against several pathogens of crucifers.