Direct Conversion of Olefins into α-Bromo Ketones Using O-Iodoxybenzoic Acid and Tetraethylammonium Bromide

Abstract

Utilizing full potential of IBX, a mild, selective, and facile method has been developed for the direct conversion of olefins into the corresponding α-bromo ketones by using 1.1 equivalents each of o-iodoxybenzoic acid and tetraethylammonium bromide.

Key words

o-iodoxybenzoic acid - tetraethylammonium bromide - α-bromo ketone

References and Notes

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16

General Experimental Procedure for Direct Conversion of Olefins into α-Bromo Ketones
To a stirred suspension of IBX (5.5 mmol) and TEAB (5.5 mmol) in anhydrous CH₂Cl₂ was added the olefine (5 mmol). Within 5-15 min the reaction mixture turned from yellow to colorless and homogeneous, indicating completion of reaction (monitored by TLC). The reaction mixture was diluted with CH₂Cl₂ (25 mL) and washed with sat. NaHCO₃ (2 × 25 mL), followed by NaHSO₃ (25 mL), and brine (25 mL). The organic layer was separated, dried over anhyd Na₂SO₄, filtered, and solvent was evaporated under reduced pressure to give the crude bromo ketone. The crude product was purified by column chromatography using silica gel (60-120), eluting with EtOAc-PE (1:99).

17

Spectroscopic Data for Selected α-Bromo Ketones
2-Bromocyclohexanone (Entry 2) Liquid.^¹³a IR (neat): ν_max = 1731, 740, 680 cm-^¹. ^¹H NMR (60 MHz, CDCl₃): δ = 1.25-2.51 (m, 8 H), 3.82-4.13 (dd, J = 1.92 Hz, 1 H).
2-Bromocyclooctanone (Entry 3) Liquid.^¹³b IR (neat): ν_max = 1730, 685 cm^-¹. ^¹H NMR (60 MHz, CDCl₃): δ = 1.25-1.59 (m, 8 H), 2.17-2.52 (m, 4 H), 4.08-4.17 (t, J = 2.9 Hz, 1 H).
1-Bromoocta-2-one (Entry 4)
Liquid.^¹4a IR (neat): ν_max = 1730, 686 cm^-¹. ^¹H NMR (300 MHz, CDCl₃): δ = 0.91-1.10 (t, J = 9.6 Hz, 3 H), 2.26-2.00 (m, 10 H), 3.74 (s, 2 H).
1-Bromo-3,3-dimethylbutan-2-one (Entry 6)
Liquid.^¹4b IR (neat): ν_max = 1730, 690 cm^-¹. ^¹H NMR (300 MHz, CDCl₃) δ = 1.14 (s, 9 H), 3.69 (s, 2 H).
1-Bromo-3-phenoxypropan-2-one (Entry 8) Liquid.^¹5a IR (neat): ν_max = 1737, 668 cm^-¹. ^¹H NMR (60 MHz, CDCl₃): δ = 4.46 (s, 2 H), 5.10 (s, 2 H), 6.99-7.34 (m, 5 H).
1-Bromo-3-(4-chlorophenoxy)propan-2-one (Entry 9)
Liquid.^¹5b IR (neat): ν_max = 1738, 668 cm^-¹. ^¹H NMR (300 MHz, CDCl₃): δ = 4.46 (s, 2 H), 5.10 (s, 2 H), 7.03 (dd, J = 8.1 Hz, 2 H), 7.38 (dd, J = 6.4 Hz, 2 H).
10-Bromo-11-oxo-10,11-dihydro-5 H -dibenzo[ b , f ]azepine-5-carboxamide (Entry 10)
Solid; mp 89 ˚C.^¹5c IR (KBr): ν_max = 3377, 3325, 3020, 1726, 1696, 744 cm^-¹. ^¹H NMR (60 MHz, CDCl₃): δ = 6.59 (s, 1 H), 6.99-7.92 (m, 8 H).