Zinc-Mediated Synthesis of Tertiary Alkyl Selenides from Tertiary Alkyl Halides

Abstract

Diorganyl selenides are efficiently synthesized from ­tertiary alkyl halides, selenols or selenolates and zinc dibromide as well as from diselenides in the presence of zinc.

Key words

substitution - alkyl halides - diorganyl selenides

References

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• 2a

  This reaction produces, besides phenyl 1-adamantyl selenide (62%), diphenyl selenide (13%) as well as di(1-adamantyl) selenide (14%).

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• 2c

  Phenyl 1-adamantyl selenide has also been synthesized in poor yield via an S_H2 process from adamantane-1-carboxylic acid, lead tetracetate and diphenyl selenide, [2d] or in good yield from 1-adamantyl trifluoroacetate and phenyl selenol. [2d]

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• 5a

  A solution of 2-bromo-2-methyl-undecane (1.24 g, 5 mmol) in anhyd CH₂Cl₂ (3 mL) was added at r.t., to a suspension of zinc (327 mg, 5 mmol) and diphenyldiselenide (780 mg, 2.5 mmol) in CH₂Cl₂ (2 mL). The suspension was stirred at r.t. for 5 h. Then, H₂O (10 mL) was added and the mixture wasextracted with Et₂O (3 × 25 mL) and washed with H₂O (3 × 20 mL). The ether layer was dried by MgSO₄ and evaporated to give an oily residue, which on purification by column chromatography (SiO₂, pentane) afforded pure 2-methyl-2-phenylseleno undecane: 1.42 g, 4.37 mmol, 87% yield.

• 5b

  Spectroscopic data: IR, ¹H NMR and ¹³C NMR, MS agree with the proposed structures. Microanalyses of novel compounds agree with the calculated values.

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11

As pointed out by a referee ‘an apparent similar reaction was reported recently in the same journal’. [8] The reaction proceeds in polar solvent and has a completely different outcome than that reported in this paper: in MeCN-H₂O it gives a different result, demonstrating no significant reaction with tertiary alkyl halides and facile reaction with primary and secondary halides. We are working in order to understand this spectacular solvent effect; less basic solvents usually favor S_N1-type reaction.