Overcoming catalytic bias

Abstract

Metathesis reactions can be used to make carbon–carbon double bonds — bar one isomeric class. By using new catalysts and balancing out the stabilities of intermediates in the reaction, the elusive isomers can be made. See Article p.461 The Z-alkene bond is one of the most important chemical bonds in nature. Many natural products contain one or several Z alkenes, consisting of a double bond with two substituents at each end pointing in the same direction. The potency or function of these natural products disappears or changes significantly if the two substituents point in opposite directions — a structure called an E alkene. Convenient methods for the stereoselective synthesis of 1,2-disubstituted Z alkenes are scarce. Amir Hoveyda and colleagues now describe catalytic Z-selective cross-metathesis reactions of terminal enol ethers and allylic amides, previously used only in E-selective processes. The potential of this reaction is demonstrated by its use in syntheses of antioxidant plasmalogen phospholipids found in electronically active tissues and implicated in Alzheimer's disease, and the potent immunostimulant and antitumour agent KRN7000.