Selenium catalysts synthesis

The e-f-fect o-f organic additives on the activity o-f a selenium catalyst in phenyl urethane synthesis by the carbonyl at i on o-f PhH02 has been studied (30. ... 

Delacote C, Bonakdarpour A, Johnston CM, Zelenay P, Wieckowski A (2009) Aqueous-based synthesis of ruthenium-selenium catalyst for oxygen reduction reacti[Pg.370]

The synthesis of optically active selenium-containing reagents as well as their application to stereoselective synthesis is of high current interest. Several products also contain a selenium functionality and their use as chiral ligands and catalysts in asymmetric reaction is promising. Various reactions of this type are known and some recent developments in this novel area are summarized here. 

With the variety of transformations that can be promoted by organopalladium reagents, it is unfortunate that palladium is such a rare metal. Biochemical processes might be much more exotic if palladium had been more abundant in the earth s crust at the origin of life (although selenium, which is an essential trace nutrient, is only approximately five times as concentrated as palladium in the earth s crust). The discovery of high turnover number catalysts has allowed several palladium-catalyzed reactions to be used in fine chemical and pharmaceutical synthesis. Naproxen (29) can be made using a Heck reaction. Ibuprofen s (30) synthesis... 

Oxyselenation ofalkeues, - Treatment of olefins with 1 or 2, water, and an acid catalyst (e.g., p-TsOH) in CH2CI2 affords j3-hydroxy selenides in excellent yield. Unsaturated carboxylic acids, phenols, alcohols, thioacetates, and urethanes react with 1 or 2 and an acid catalyst ( —78- 25°) to afford products of oxidative cyclization. These reagents are superior to benzeneselenenyl halides for selenium-induced ring closures. This reaction is also useful for synthesis of 14- and 16-membered lactones. Benzeneselenenyl halides and benzeneselenenic acid do not promote macrolide formation under similar conditions. 

The synthesis of diphosphaseleniranes 18 by treating diphosphenes with selenium has already been discussed in <1996CHEC-II(1)457>. The method has been extended to asymmetric compounds <1995HAC33>, as shown in Scheme 14. The reaction proceeds at 60 °C in benzene when pyridine is used as a catalyst. The compound 18a was isolated by column chromatography as a stable colorless crystalline solid in 37% yield, although 18b and 18e were not stable enough to permit isolation by the method which was employed for 18a. 

Synthesis of ureas. Ureas can be synthesized by the reaction of aliphatic amines, carbon monoxide, and oxygen with selenium as a catalyst. For example, n-butylamine (0.1 mole) is dissolved in THF (100 ml.) amorphous selenium (0.005 g.-atom) is added and carbon monoxide is blown through the solution. Then oxygen (or air) is blown through. 1,3-Di-n-butylurea is obtained in stoichiometric yield. The reaction proceeds in two steps as formulated. 

---