Gold catalysis: Experimental mechanistic insights into the anellation of phenols with 1,3-dienes

• An intermediate of the reaction could be isolated.
• It could be identified as the hydroarylation intermediate.
• The other conceivable intermediate, the hydroaryloxylation intermediate, was prepared by an independent route.
• A much slower reaction of the hydroaryloxylation intermediate excluded a significant contribution in the product formation.

An intermediate of the anellation reaction of phenols and 1,3-dienes could be detected, isolated and characterized as the hydroarylation product. The other conceivable intermediate, the hydroaryloxylation product, was prepared via Pd-catalysis and converted under the conditions of the gold catalysis, too. Under exactly the same conditions a very fast Claisen rearrangement took place delivering the formal hydroarylation product as well. After this fast intermolecular formation of the intermediate (formed either directly via the hydroarylation pathway or via a hydroaryloxylation/Claisen rearrangement sequence) the subsequent intramolecular reaction leading to the product turned out to be significantly slower. The major product is the cis-diastereomer (cis-3/trans-3 = 12:1).

The intermolecular addition is faster than the intramolecular addition. Experimental studies reveal that the key intermediate can be formed via two different pathways including a fast Claisen rearrangement that enables the interconversion of the two possible intermediates.Figure optionsDownload as PowerPoint slide