Stereoselective De Novo Synthesis of Substituted Cyclopentanes via a Gold(I)‐Catalyzed (3 + 2) Cycloaddition of Enamides

A general and stereoselective synthesis of highly substituted cyclopentylamine scaffolds is reported starting from various N‐alkenyl‐amides. The reaction involves the generation of an aurated dithioallyl cation which undergoes a classical stepwise (3 + 2) allyl cation cycloaddition with a range of enamide substrates. The close coordination of the reactive intermediates with the well‐defined gold(I)‐catalyst results in a reactivity and selectivity profile that can be readily rationalized on the basis of a nonconcerted carbocationic cycloaddition reaction, and some remarkable counterion effects are seen to effect the chemoselectivity of the overall process.