Recyclable heterogeneous gold(i)-catalyzed oxidative ring expansion of alkynyl quinols: a practical access to tropone and its analogues

Abstract

The heterogeneous gold(I)-catalyzed oxidative ring expansion of alkynyl quinols has been achieved by using a benzyldiphenylphosphine-modified MCM-41-immobilized gold(I) complex [MCM-41–BnPh₂P–AuNTf₂] as the catalyst and 8-methylquinoline N-oxide as the oxidant under mild reaction conditions, yielding a variety of functionalized tropone derivatives in good to excellent yields. Extension of this methodology allows for facile construction of other seven- or six-membered ring systems including dibenzotropones, dibenzooxepines, phenanthrenes, and quinolin-2(1H)-ones. This new heterogeneous gold(I) complex can be readily recovered through a simple filtration process and recycled at least eight times without any apparent decrease in catalytic efficiency.