Selectivity control by silver catalysts in the cycloisomerization of 1,6-enynes derived from propiolamides

Silver-catalyzed cycloisomerizations of 1,6-enynes derived from propiolamides led to a selective formation of Alder-ene type 1,4-dienes. Interestingly, AgNTf2 outperformed gold or platinum catalysts in terms of selectivity and reactivity, providing the 1,4-dienes at room temperature. The presence of C(5) carbonyl group in combination with Ag salts is key to the selectivity and the β-oxo coordinated silver carbenoids were proposed as an intermediate based on the reaction profiles.