On activation with catalytic amounts of gold(I) complexes, 3-silyloxy 1,6-enynes can react through two alternative pathways. In one, a cascade reaction consisting of carbocyclization and subsequent pinacol rearrangement takes place. In the second pathway, a heterocyclization is followed by a Claisen rearrangement. The reaction outcome differs depending on the substitution pattern of the 3-silyloxy 1,6-enynes and, more importantly, the electronic properties of the gold-bound phosphane ligand.

Golden reactivity: A new gold(I)‐catalyzed cycloisomerization of 3‐methoxy‐1,6‐enynes was discovered. Structurally simple 3‐methoxy‐1,6‐enynes engage in a tandem cyclization/[3,3]‐sigmatropic rearrangement to deliver a variety of 1‐methoxy‐1,4‐cycloheptadienes (see scheme). Notably, the reaction can be performed under very mild conditions and the synthetic utility of this reaction was demonstrated by facile conversion of the product into various cyclohept‐4‐en‐1‐ones.

A new gold(I)-catalyzed cycloisomerization to access highly substituted piperidines has been developed. By combining a conceptually new way of generating iminium ions using cationic gold(I) complexes and an efficient cyclization reaction that can minimize a potentially competing aza-Cope rearrangement, the proposed reaction successfully circumvents a long-standing problem in the classical aza-Prins reaction. Synthetic utility of the catalytic reaction was demonstrated by a synthesis of optically active 2-alkyl-piperidin-4-one.

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