Conditions-Driven Selective Synthesis of Selenides and Selenols from Elemental Selenium

Abstract

Sodium borohydride in DMF is able to reduce elemental selenium in the presence of ethanol. Alkylation of the species resulting from the reaction of 2:1 molar equivalents of NaBH₄/Se allows the selective synthesis, under very mild conditions, of symmetrical dialkyl selenides. Addition of formic acid, prior to that of the electrophile, permits the synthesis of the corresponding selenols.

Key words

elemental selenium - sodium borohydride - alkylation - alkyl halides - benzyl halides

References

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  The reaction between sodium borohydride (2 equiv) and selenium, carried out in pure DMF also leads to a complex that can be successfully alkylated to 1¢ but contaminated by a minor impurity difficult to separate from 1¢. However, these conditions do not allow the synthesis of the selenol 3 if formic acid is added prior to the alkylating agent (compare to Scheme [4] ).

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6

In the course of this work we have found that whereas decyl selenol 3a does not react with decyl bromide or methyl iodide in DMF, it can be alkylated if the reaction is carried out in the presence of sodium formate (1 equiv). The reaction is quite slow (20 °C, 20 h) and provides competitively some diselenides 2 resulting from the oxidative coupling of the selenolates.