Gold(I)‐Catalysed Hydroarylation of Lactam‐Derived Enynes as an Entry to Tetrahydrobenzo[g]quinolines.

The gold(I)‐catalysed cyclization of N‐tosyl‐protected 5‐benzyl‐6‐((trimethylsilyl)ethynyl)‐1,2,3,4‐tetrahydropyridines, prepared by the Sonogashira coupling of lactam‐derived enol triflates, provides tetrahydrobenzo[g]quinolines whose skeleton represents a recurrent motif in natural compounds. The Au(I)‐catalysed reaction is carried out with (C6F5)3PAuCl/AgNTf2 as the catalyst system and proceeds via a 6‐exo‐dig cyclization to form an exocyclic double bond, which eventually isomerises to the aromatic tetrahydrobenzo[g]quinoline. The mode of cyclization is discussed and supported by DFT calculations. [ABSTRACT FROM AUTHOR]