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Synlett 2006(16): 2601-2604  
DOI: 10.1055/s-2006-951470
LETTER
© Georg Thieme Verlag Stuttgart · New York

Synthesis of Hexylselenol and Hexylselenides from Hexylthiol Involving ­Hexylthiolanium Salts

Alain Krief*a, Willy Dumonta, Michael Roberta,b
a Laboratoire de Chimie Organique de Synthèse, Facultés Universitaires N.-D. de la Paix, 61 rue de Bruxelles, Namur, 5000, Belgium
Fax: +32(81)724536; e-Mail: alain.krief@fundp.ac.be;
b Fonds pour la Formation à la Recherche dans l’Industrie et l’Agriculture, 5 rue d’Egmont, Bruxelles 1000, Belgium
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Publication History

Received 5 July 2006
Publication Date:
22 September 2006 (online)

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Abstract

Selenium nucleophiles react regioselectively at the endo­cyclic or exocyclic carbon of hexylthiolanium salts depending upon the nature of the salt.

Key words

halides - S-alkylations - selenium - nucleophiles

    References and Notes

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  • 2b

    It is necessary to employ 1.5 equivalents of 1,4-dibromo-butane to avoid competing formation of 1,4-di(hexylthio)butane; the latter is produced in up to 16% yield along with 3b (75%) if a stoichiometric amount of the substrate is used.
    Article in Thieme Connect
  • 2c

    1-Bromo-4-chloro-butane behaves similarly to 1,4-dibromo-butane.
    Article in Thieme Connect
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  • 7a

    S -1-Hexylthiolanium Bromide: A mixture of hexane-thiol (590 mg, 5.0 mmol), 1,4-dibromobutane (1.6 g, 1.5 equiv, 7.5 mmol), and K2CO3 (690 mg, 1.5 equiv, 5.0 mmol) in EtOH (10 mL) was stirred at r.t. for 5 h under argon. EtOH was then removed, the residue was suspended in CHCl3, and KBr was removed by filtration. CHCl3 was removed under vacuum, the resulting oil was first triturated with anhyd Et2O and then dried under vacuum to produce 1.1 g of the oily S-1-hexylthiolanium bromide (86% yield of crude product).

  • 7b

    1-Hexylselenocyanate: A solution of S-1-hexylthiolanium bromide (254 mg, 1 mmol) in DMF (1 mL) was added at r.t. to a stirred solution of KSeCN (143 mg, 1 mmol) in DMF (1 mL). The resulting solution was stirred at 80 °C for 24 h, cooled to r.t., then washed with H2O (5 mL) and extracted with Et2O (3 × 5 mL). The organic layer was washed with H2O (2 × 5 mL) and dried over MgSO4. After filtration, the solvent was evaporated under vacuum (10 mm Hg). Purification of the resulting liquid by preparative TLC (silica gel; pentane-Et2O, 9:1) leads to 1-hexylselenocyanate (6; 130 mg, 68% yield).

  • 7c

    Hexylselenol: NaBH4 (190 mg, 5 mmol) was added at r.t., in small portions, to a stirred solution of hexylseleno-cyanate (950 mg, 5 mmol) in EtOH (5 mL). After 0.2 h, aq HCl (10%) was added. The resulting solution was extracted with Et2O (3 × 20 mL), the organic layer was washed with H2O (2 × 5 mL) and then dried over MgSO4. After filtration and evaporation of the solvent the residue was distilled to give hexylselenol (82 °C, 20 mm Hg, 638 mg, 75% yield).

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  • 9b

    For a related reaction recently performed on thiolates see ref. 1a.
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5

We have also performed this reaction successfully in acetone. On mixing a solution of KSeCN (1 mmol) in acetone (3 mL) at r.t. with a solution of the tetrafluoroborate 3c (1 mmol) in the same solvent (1 mL), a red-brown solid precipitates almost instantaneously. This solid mainly contains potassium tetrafluoroborate and some KSeCN, which co-precipitates. The resulting solution [IR (neat): 2060 cm-1 (s), attributed to the selenocyanate anion] slowly delivers 1-hexyl 1-(4-selenocyanato)butyl sulfide (8; 20 °C, 72 h, 3c/8: 39:61). Evaporation of acetone and distillation of the residue (short-path distillation, 150 °C, 200 mmHg) leads to 6 in 68% yield; IR(neat): 2150 cm-1 (s), attributed to the selenocyanato group attached to an alkyl chain.

6

Prepared from potassium selenocyanate and 1,4-dibromo-butane. IR and NMR spectra support this assignment rather than that of its cyclic isomer.