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This is an open access article published under an ACS AuthorChoice License, which permits copying and redistribution of the article or any adaptations for non-commercial purposes. Article /joc Regio- and Stereoselective Monoepoxidation of Dienes using Methyltrioxorhenium: Synthesis of Allylic Epoxides Saroj Ranjan De, Ganesh Kumar, Jawahar L. Jat, Saritha Birudaraju, Biao Lu, Rajkumar Manne, Narender Puli, Adeniyi Michael Adebesin, and John R. Falck* Division of Chemistry, Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, Texas 75390, United States S *Supporting Information ABSTRACT: Methyltrioxorhenium (MTO) complexed with pyridine was shown to be a highly effective catalyst for the regioselective monoepoxidation of conjugated di- and trienes using 30% H2O2 at or below room temperature. The resultant allylic epoxides, and the triols derived from them, are versatile synthetic intermediates as well as substructures present in many bioactive natural products. The site of epoxidation was dependent upon olefin substitution, olefin geometry (Z vs E), and the presence of electron-withdrawing substituents on adjacent carbons. For 1-acyl(silyl)oxypenta-2,4-dienes, epox- idation of the distal olefin was generally favored in contrast to the adjacent regioselectivity characteristic of Sharpless, peracid, and other directed epoxidations of hydroxylated dienes. ■ INTRODUCTION An array 1 of protocols is available fo