Gold(I)-Catalyzed 5-endo Hydroxy- and Alkoxycyclization of 1,5-Enynes: Efficient Access to Functionalized Cyclopentenes

摘要

The cyclopentyl unit is found frequently in a wide variety of natural products that exhibit biological activity.[1] As a consequence, the development of practical synthetic routes to form five-membered rings remains of interest. Gold(I) complexes have emerged as efficient and mild catalysts for the activation of alkynes towards addition by a variety of nucleophiles,[2] and their potential has been highlighted by numerous studies related to the conversion of enynes into cycloisomerized products.[3] For example, Echavarren and co-workers reported that 1,6-enynes of type 1 could be transformed into cyclopentadienes of type 3 [Eq. (1a)].[4] The same substrates also underwent a 5-exo alkoxycyclization to furnish the exo-methylenecyclopentane derivatives of type 4 when an alcohol was used as the solvent [Eq. (1b)].