Gold-catalyzed reactions of 1,5- and 1,6-enynes with carbonyl compounds: Cycloaddition vs. metathesis

The gold(I)-catalyzed addition of aldehydes to 1,6-enynes gives 1,3-dienes, by a cycloaddition/fragmentation process. 1,5-Enynes react with aldehydes and ketones by the 5-endo-dig pathway to give the corresponding cycloadducts.