Direct Reaction of Aryl Iodides with Activated Aluminium Powder and Reactions of the Derived Aryl Sesquiiodides

Abstract

High temperature (110-120 ˚C) direct reaction of ArI (Ar = Ph, 1-C₁₀H₇, 3-Tol) with aluminium powder in the presence of HgCl₂ (1 mol%) or liquid gallium metal (10 mol%) leads to quantitative conversion to the aryl sesquiiodides Al₂Ar₃I₃. The latter, highly Lewis acidic, compounds are effective in opening of cyclic ethers and direct ester to amide conversions.

Key words

organometallic reagents - Lewis acids - amides - halides - electron transfer

References and Notes

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16

General Procedure for the Synthesis of Sesquihalide; Method 1: Aluminium powder (81 mg, 3 mmol) and HgCl₂ (5 mg, 0.02 mmol) were added to a dry argon-flushed Schlenk tube. Organohalide (2 mmol) was added and the reaction was stirred at 120 ˚C for 3 h. Anhydrous toluene (1 mL) was added and the mixture was stirred vigorously for 5 min. The reaction mixture was allowed to cool to r.t. and left for 30 min for the excess aluminium metal to settle. The light brown supernatant solution of organoaluminium sesqui-halide was ready to use. Method 2: Aluminium powder
(59 mg, 2.2 mmol) and Ga (14 mg, 0.2 mmol) were added to a dry argon-flushed Schlenk tube. Organohalide (2 mmol) was added and the reaction was stirred at 120 ˚C for 20 h. Anhydrous toluene (1 mL) was added and the mixture was stirred vigorously for 5 min. The reaction mixture was allowed to cool to r.t. and left for 30 min for the excess aluminium metal to settle. The light brown supernatant solution of organoaluminium sesquihalide was ready to use.

17

General Procedure for Reactions of Sesquihalide and Acetyl Chloride: Acetyl chloride (1 mmol) was dissolved in anhydrous toluene (2 mL), and sesquihalide (1 mmol) prepared by method 2 was added. The reaction mixture was stirred at r.t. for 3 h. The reaction was quenched with HCl (2 M) and extracted with Et₂O. The organic phase was dried over MgSO₄ and concentrated to give the crude compound. The crude material was purified by column chromatography (light petroleum-Et₂O) over silica gel to give the pure product.

22

General Procedure for Amide Formation: Amine
(1 mmol) was dissolved in anhyd toluene (2 mL), and sesqui-halide (0.67 mmol) prepared by method 2 was added. The reaction mixture was stirred at r.t. for 10 min. The ester (0.5 mmol) was added to the reaction mixture and the mixture was heated to 80 ˚C for 3 h. The reaction was quenched with HCl (2 M) and extracted with Et₂O. The organic phase was dried over MgSO₄ and concentrated to give the crude compound. The crude material was purified by column chromatography (light petroleum-Et₂O) over silica gel to give the pure product.