Intramolecular Cycloaddition of 1,3-Enynes with Alkenes

By: William Sommer, Aldrich ChemFiles 2009, 9.5, 5.

Aldrich ChemFiles 2009, 9.5, 5.

In 2008, Echavarren and co-workers in their quest for finding more active gold catalysts for new reactions, reported the synthesis of pycnantuquinones A derivatives, catalyzed by [4+2] cycloaddition of dienynes.1 Usually, [4+2] cycloadditions of enynes with alkenes take place at high temperature, making it sometimes incompatible with the substitution pattern of the substrate. Using a stable crystalline gold complex based on a biphenyl phosphine JohnPhos ligand, and bulky aryl ether phosphine with mild conditions, the researchers were able to synthesize a family of bi- and tricyclic systems with good yields (Scheme 13). Through the study and understanding of the mechanism of this reaction, it was noted that aryl substituents stabilize intermediate gold carbenes, therefore facilitating the anti to syn isomerization. It is also important to note that the reactions tolerate an electronic and steric variety of functional groups on the aryl.

Scheme 13.

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  1. Nieto-Oberhuber, C. et al. J. Am. Chem. Soc. 2008, 130, 269.

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