[59957-75-4] · C10H8N2Se2 · 2,2´-Dipyridyl Diselenide · (MW 314.12)
Physical Data: mp 50 °C.
Solubility: sol THF, acetonitrile, dichloromethane, methanol.
Preparative Methods: by reaction of 2-bromopyridine with Sodium Hydrogen Selenide (prepared from Selenium and Sodium Borohydride) in ethanol followed by oxidation1,4 or with Lithium Diselenide (prepared from selenium and Lithium in the presence of Diphenylacetylene as catalyst) in THF-HMPA.6
Purification: column chromatography on silica gel using hexane-ethyl acetate (2:1) or light petroleum ether-ethyl ether (1:1) as eluent. Recrystallization from petroleum ether (30-70 °C) or diisopropyl ether-ethyl acetate.
Handling, Storage, and Precautions: the reaction of sodium hydrogen selenide should be carried out in a well-ventilated hood (H2, containing H2Se, is produced). Selenium is reputed to be toxic. 2,2´-Dipyridyl diselenide should be stored in the dark.
In the selenoxide elimination reactions to afford alkenes, the 2-pyridineseleninyl group has been reported to be a better leaving group than the benzeneseleninyl group. Typical examples are the formation of cyclooctenone1 and monosubstituted terminal alkenes.7 2,2´-Dipyridyl diselenide was used in the preparation of starting selenides, for example 2-(2-pyridylseleno)cyclooctanone, by reaction with the lithium enolate of cyclooctanone (eq 1). In another method, 2,2´-dipyridyl diselenide was treated with sodium borohydride to afford sodium 2-pyridineselenolate, which was used in the subsequent nucleophilic substitution reactions (eq 2).
In the Ritter-type substitution of a hydroxy group by nitriles through the anchimeric assistance of the areneselenenyl group onto the chiral carbon, chiral amides were obtained without loss of optical purity by the use of the 2-pyridineselenenyl group (eq 3), whereas racemic amides were obtained by the use of the benzeneselenenyl group. Subsequent oxidation of the selenides to selenones and treatment with base induces the intramolecular substitution of the 2-pyridineselenonyl group by the oxygen atom of the amide to afford chiral oxazolines (eq 4).3
A combination of 2,2´-dipyridyl diselenide and Triphenyl Phosphite has been utilized in the synthesis of oligonucleotides (eq 5).4 This reagent has been reported to be superior to sulfur analogs such as 2,2´-Dipyridyl Disulfide and Triphenylphosphine8 in that the reaction using this combination is free from undesirable byproducts. A combination of 2,2´-dipyridyl diselenide and triphenylphosphine has also been used in the selective phosphorylation of 5´-hydroxy group of oligoribonucleotides.9
2,2´-Dipyridyl diselenide catalyzes the oxidation of alkenes to unsaturated ketones by Iodylbenzene (eq 6).5 The reactive species is considered to be 2-pyridineseleninic anhydride, which is much more reactive to alkenes than benzeneseleninic anhydride.
Kyoto University, Japan