Pd-Catalyzed Cascade Cyclization by Intramolecular Heck Insertion of an Allene-Allylic Amination Sequence: Application to the Synthesis of 3,4-Fused Tricyclic Indoles

A novel Pd-catalyzed cascade cyclization by intramolecular Heck insertion of an alleneallylic amination sequence was developed. Allenes tethered to ortho-iodoaniline derivatives at the meta-position were reacted with 5-10 mol % of Pd catalyst and 4 equiv of K2CO3 in DMSO at 90 degrees C, producing 3,4-fused tricyclic 3-alkylidene indoline derivatives in moderate to excellent yield. The reaction products were divergently transformed into three types of 3,4-fused tricyclic indole derivatives, successfully demonstrating the versatile properties of the reaction products.