Abstract
Treatment of 2-epoxy-1-alkynylbenzenes with electron-rich alkenes and a [AuCl(PR 3 )]/AgX catalyst in CH 2 Cl 2 led to the formation of 2-alkenyl-1-(2,3-dihydrofuran-4-yl)benzenes. This transformation comprises of a gold-catalyzed redox reaction to form a gold α- carbonylcarbenoid initially, which then reacts in situ with an alkene in a [3+2] cycloaddition. A range of alkenes are amenable to this tandem reaction, amongst them α-sub-stituted styrenes, enol ethers, and 2,3dimethylbutadienes. Deuterium-labeling experiments suggest a stepwise mechanism for the α-carbonylcarbenoid/alkene [3+2] cycloaddition. The resulting 2,3-dihydrofuran products allow access to diverse oxacyclic compounds through a stereoselective ene-oxonium reaction initiated by treatment with HOTf (1mol%; Tf= trifluoromethanesulfonyl). A stepwise pathway is proposed for this reaction. The feasibility for direct transformation of 2-alkenyl-1-alkynylbenzenes into the desired 2,3-dihydrofuran products through initial m-chloroperbenzoic acid oxidation, followed by the addition of gold catalyst and alkene, has also been demonstrated. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA.