[4371-90-8] · C2H6OSe · Dimethyl Selenoxide · (MW 125.03)
Physical Data: mp 94 °C.
Solubility: sol water, ethanol, acetone, chloroform.
Preparative Methods: readily obtained by oxidation of dimethyl selenide with 30% aqueous Hydrogen Peroxide at -10 °C, or with Ozone in chloroform at -50 °C; also prepared by treating dimethylselenium dibromide with Silver(II) Oxide in methanol.
Purification: recrystallization from benzene gives the pure material as colorless needles.
Handling, Storage, and Precautions: hygroscopic; decomposes in ether, acetonitrile, THF, and CS2; since the reactions of dimethyl selenoxide often produce volatile organoselenium derivatives having a highly unpleasant odor, use in a well-ventilated fume hood.
Several selenoxides, such as dimethyl selenoxide,1,2 dibenzyl selenoxide,6 diphenyl selenoxide,7 and bis(p-methoxyphenyl) selenoxide,8 are mild and selective agents for the oxidation of various functional groups. Dimethyl selenoxide oxidizes trivalent phosphorus compounds and thio- and selenophosphonyl compounds to their oxygenated analogs more effectively than Dimethyl Sulfoxide.1 The reactions for the acyclic derivatives occur with nearly complete inversion of configuration (eq 1) and for cyclic derivatives with almost full retention (eq 2). The reagent also oxidizes thioureas and thiouracils to the corresponding carbonyl compounds in high yields. This reaction is useful for selective modifications of the 4-thiouracil group in transfer ribonucleic acids (eq 3).
The oxidation of halomethylarenes with dimethyl selenoxide in refluxing 1,2-dichloroethane gives polysubstituted aromatic aldehydes bearing substituents reactive toward acids, bases, or water (eq 4).2
The reagent reacts with alkenes in AcOH-CHCl3 at 60 °C to give 2-acetoxyalkyl methyl selenides (eqs 5 and 6).3 This addition reaction is regioselective and trans stereospecific. Presumably MeSeOAc is the reactive species.
Dimethyl selenoxide effects electrophilic substitution of phenols in the presence of hydrogen chloride at 0-20 °C to give dimethyl(hydroxyphenyl)selenonium chlorides, whose pyrolyses in refluxing toluene afford methyl hydroxyphenyl selenides in high yields (eq 7).4
The substitution reaction of 5-(trimethylsilyl)cyclopentadiene with dimethyl selenoxide forms the selenoniocyclopentadienide in an excellent yield (eq 8).5 Similar reactions of pentafulvene, indole, and pyrrole give the corresponding selenonium salts.
Fumio Ogura & Tetsuo Otsubo
Hiroshima University, Japan