[65857-68-3] · C4H10NaO3PTe · Sodium O,O-Diethyl Phosphorotelluroate · (MW 287.69)
Solubility: sol ethanol, tetrahydrofuran.1
Preparative Methods: 1 generated in situ by addition of ethanolic sodium diethyl phosphite to metallic tellurium. When made separately, the reagent is best formed in THF. This solvent can then be replaced by ethanol, which is the best solvent for epoxide deoxygenation.
Handling, Storage, and Precautions: the reagent is extremely air sensitive and is preferably made just before use or, more simply, generated in situ.1
Sodium O,O-diethyl phosphorotelluroate and the lithium salt, which is more reactive, deoxygenates epoxides to the corresponding alkenes. The reaction occurs in ethanol solution but in THF is too slow to be useful. Reaction takes place most easily with terminal epoxides and it can be run for these cases, as well as for certain others, by using much less than a stoichiometric amount (e.g. 2-20 mol %) of tellurium. For such experiments, sodium diethyl phosphite is added to a stirred mixture of the epoxide, Tellurium, and ethanol. When used stoichiometrically, the reagent is made in THF, and the solvent is evaporated and replaced by ethanol. The deoxygenation is stereospecific and epoxides derived from (Z)-alkenes are more reactive than those from (E)-alkenes. Reaction occurs more easily with cyclohexene oxide than with cyclopentene oxide. Typical deoxygenations are shown in eqs 1-4.
a-Bromo and a-chloro ketones, on treatment with sodium O,O-diethyl phosphorotelluroate in ethanol or THF, are converted into the parent ketone. Reaction proceeds in the temperature range 25-80 °C and reaction times vary from 45 min to 15 h. For highest yields, a stoichiometric amount of reagent is best, but a catalytic amount of tellurium and a stoichiometric amount of sodium diethyl phosphite can also be used. The catalytic mode is possible because sodium O,O-diethyl phosphate reacts only slowly with a-bromo ketones, but rapidly with tellurium, and the reagent itself reacts rapidly with a-halo ketones. The selenium analog, sodium O,O-diethyl phosphoroselenoate, does not appear to dehalogenate a-bromo ketones,2 the selenium atom merely being alkylated. Typical results with the tellurium reagent are shown in eqs 5 and 6.
Vicinal dibromides are converted (2.5-10 h at rt; 64-88% yields) into the corresponding alkenes by treatment in ethanol with sodium diethyl phosphite and a catalytic amount of tellurium (eqs 7 and 8). The alkene geometry corresponds to removal of the bromine from an antiperiplanar conformation.
2-Bromoacetophenone has been converted into a series of a,b-unsaturated ketones (eq 9) by treatment with an aldehyde in ethanol in the presence of sodium O,O-diethyl phosphorotelluroate (77-93% yield).
Aryl sulfonyl chlorides are converted by sodium O,O-diethyl phosphorotelluroate into the corresponding sodium sulfinates. These then react in situ with alkyl halides to afford sulfones in 77-94% yield (eq 10).
Philip L. Wickens & Derrick L. J. Clive
University of Alberta, Edmonton, AB, Canada