Sequential combination of ruthenium-, base-, and gold-catalysis - A new approach to the synthesis of medicinally important heterocycles

Abstract

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(PPh3)]/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. A novel process for the synthesis of highly substituted, medicinally important heterocycles was achieved through the sequential combination of ring-closing methathesis, base-induced ring opening, hydroamination, and Diels-Alder reaction of functionalized allyl-(2-allylphenyl) amines in the presence of a catalytic amount of [Ru], base, and [Au] (see scheme). Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.