Indole → 2-iodo-1H-indole
Reaktionsgleichung
C([Li])CCC.[NH:6]1[C:14]2[C:9](=[CH:10][CH:11]=[CH:12][CH:13]=2)[CH:8]=[CH:7]1.[I:15]CCI.[NH4+].[Cl-]>C1COCC1.O>[I:15][C:7]1[NH:6][C:14]2[C:9]([CH:8]=1)=[CH:10][CH:11]=[CH:12][CH:13]=2Komponenten
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C([Li])CCC.[NH:6]1[C:14]2[C:9](=[CH:10][CH:11]=[CH:12][CH:13]=2)[CH:8]=[CH:7]1.[I:15]CCI.[NH4+].[Cl-]>C1COCC1.O>[I:15][C:7]1[NH:6][C:14]2[C:9]([CH:8]=1)=[CH:10][CH:11]=[CH:12][CH:13]=2
2-iodoindole is prepared according to the following procedure: n-butyllithium (4.2 mL, 2.5 M in solution in hexane) is added, dropwise, to a solution of indole (1.17 g, 10 mmol) in 20 mL of anhydrous THF at −70° C. The resulting suspension is left under stiffing at this temperature for 30 minutes then gaseous CO2 is bubbled through for 10 minutes. The solution which has become clear is then left under stirring for 10 minutes. The solvent and the excess CO2 are evaporated off under vacuum then the resulting solid residue is put into solution in 20 mL of anhydrous THF and cooled down to −70° C. t-butyllithium (6.2 mL; 1.7 M in solution in pentane) is then added dropwise then the resulting solution is left under stirring for 1 hour. 1,2-diiodoethane (2.82 g; 10 mmol) is then added. The reaction mixture is left at −78° C. for 1 hour then treated with 1 mL of water. The resulting solution is left to return to ambient temperature then it is treated with a saturated aqueous solution of NH4Cl. It is extracted with ether. The organic phase obtained is washed with a saturated aqueous solution of NaCl, dried over anhydrous MgSO4 and evaporated under vacuum. The solid residue obtained is purified by flash chromatography on silica gel (hexane/ether, 4/1) producing 2-iodoindole (2.19 g; 9 mmol) with a yield of 90%. The physical and spectral data are described in the article.
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