Abstract
In the presence of strong acids in aqueous and anhydrous media alkyl aryl ketones bearing a strong electron-releasing group in the aromatic ring undergo protiodeacylation. In a reaction with triflic acid in aromatic solvents, the transfer of the liberated acyl group to aromatic solvent molecules is observed. The effects of the nature and the position of the activating group and the strength of the acid and the solvent, on the course of this ipso -substitution were investigated.
Key words
protiodeacylation - transacylation - ketones - retro-Friedel-Crafts reaction -
ipso -electrophilic-aromatic substitution
References and Notes
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General Procedure for the Reaction with Aqueous Acid
2 O or 1 mL of 50% TfOH in H2 O) was added, and refluxed for 48 h. The reaction mixture was cooled, diluted with H2 O (20 mL) and extracted with CH2 Cl2 (4 × 5 mL); the combined organic phases were washed with a sat. aq solution of NaHCO3 , dried over anhyd Na2 SO4 , and evaporated. The products were identified by 1 H NMR spectroscopy and GC-MS.
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10 1 H NMR: δ = 2.09 (q, 2 H, J = 6.2 Hz, 3-CH2 ), 2.67 (t, 2 H, J = 6.2 Hz, 5-CH2 ), 2.90 (t, 2 H, J = 6.1 Hz, 2-CH2 ), 6.70 (dd, 1 H, J
1 = 8.4 Hz, J
2 = 0.9 Hz, 5-H), 6.79 (d, 1 H, J
1 = 8.4 Hz, 7-H), 7.35 (t, 1 H, J = 8.4 Hz, 6-H), 12.43 (s, 1 H, 8-OH). GC-MS: [M+ ] = 162; [M] = 162.185 g/mol; spectrum is identical to the literature. See: Couche E.
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General Procedure for the Reaction with Anhydrous Acid
A ketone (100 mg) was dissolved in dry aromatic solvent (5 mL), TfOH (0.2 mL) was added, and the mixture was refluxed under argon. After 72 h the mixture was cooled, diluted with H2 O (15 mL), and the organic layer was separated. The water layer was extracted with CH2 Cl2 (2 × 10 mL); combined organic phases were washed with a sat. aq solution of NaHCO3 , dried over anhyd Na2 SO4 , and evaporated. The mixture of compounds was analyzed by means of GC-MS.
