Metal-Mediated Debromination of gem-Dibromoalkenes under Mild Conditions

Abstract

We describe the facile and efficient metal-promoted reduction of C–Br bonds of gem-dibromides. When the reaction is mediated by indium, the corresponding vinyl bromides are obtained in good yields and high E-stereoselectivities. Alternatively, when the reduction is mediated by samarium diiodide, vinyl bromides are obtained in moderate yields and good Z-selectivities.

Key words

dehalogenation - reduction - indium - samarium - vinyl bromides - stereoselectivity

• References and Notes

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• 17 Samarium-Promoted Reduction of gem-Dibromoalkenes 1 (Method A); General Procedure A 0.1 M solution of SmI₂ in THF (0.8 mmol) was added to a stirred solution of the appropriate gem-dibromoalkene 1 (0.4 mmol) in THF (5 mL). Deoxygenated H₂O (0.5 mL) was added and the mixture was stirred at r.t. for 3 h. The reaction was quenched with 0.1 M aq HCl (10 mL) and the mixture was extracted with CH₂Cl₂ (3 × 25 mL). The combined organic extracts were washed with sat. aq Na₂S₂O₃ (20 mL), dried (MgSO₄), filtered, and concentrated in vacuo.
• 18 Indium-Promoted Reduction of gem-Dibromoalkenes 1 (Method B); General Procedure Indium metal (90 mg, 0.8 mmol), InCl₃ (88 mg, 0.4 mmol), and Pd(PPh₃)₄ (18 mg, 2 mol%) were added to a solution of the gem-dibromoalkene 1 (0.4 mmol) in THF–H₂O (1:1; 6 mL), and the mixture was stirred at r.t. for 3 h. The reaction was quenched with 1 M aq HCl (3 mL) and the mixture was diluted with H₂O (25 mL) and extracted with Et₂O (3 × 25 mL). The organic extracts were dried (Na₂SO₄), filtered, and concentrated under reduced pressure.
• 19 The physical data for compounds 2 were similar to those reported in the corresponding literature; see refs. 2 and 3.