Sequential Combination of Ruthenium‐, Base‐, and Gold‐Catalysis – A New Approach to the Synthesis of Medicinally Important Heterocycles

A general approach to the high-yielding synthesis of medicinally important heterocycles was achieved through the sequential combination of ring-closing metathesis, base-induced ring opening (BIRO), hydroamination, and a Diels-Alder reaction of functionalized allyl-(2-allylphenyl)amines in the presence of a catalytic amount of Grubbs' second-generation catalyst, base (tBuOK), and [AuCl(PPh 3 )]/AgOTf. Herein, we also demonstrate the important electronic factors in the BIRO of N-substituted-benzo[b]azepines for the regioselective synthesis of functionalized (Z)-N-substituted-2-(buta-1,3-dienyl)phenylamines in very good yields with high purity; these are very good, useful compounds in medicinal chemistry. We also discovered the selective cascade synthesis of privileged hexahydrophenanthridines from (Z)-N-substituted-2-(buta-1,3-dienyl)phenylamines by gold catalysis in moderate to good yields with >99 % diastereomeric excess. The possible reaction mechanism for the unusual hydroamination followed by [4+2] cycloaddition of functionalized (Z)-N-substituted-2-(buta-1,3-dienyl)phenylamines through gold catalysis is discussed in this work.