16
A Typical Procedure for DIB-LiBr Bromination: To a solution of substrate (5 mmol) and LiBr (0.48 g, 5.5 mmol) stirring in anhyd THF at r.t. in an open vessel DIB was added portionwise over 5 min (1.77 g, 5.5 mmol). The suspension was stirred for a further 25 min, water added (10 mL) and the reaction mixture extracted with CH2Cl2 (20 mL). The organic layer was washed with water (20 mL) and brine (20 mL), dried over MgSO4 and concentrated in vacuo, and chromatographed (isooctane-Et2O) to give the brominated product.
17
4-Bromanisole (Table
[1]
, entry 1): Yield: 88%; colourless oil. 1H NMR (400 MHz, CDCl3): δ = 7.36 (d, J = 9.0 Hz, 2 H, ArH), 6.76 (d, J = 9.0 Hz, 2 H, ArH), 3.76 (s, 3 H, CH3). 13C NMR (68 MHz, CDCl3): δ = 158.7, 132.4, 115.8, 112.9, 55.4. MS (EI): m/z = 186, 188 [M+·]. HRMS: m/z calcd for C7H7O79Br: 185.9680; found: 185.9697. 6-Bromo-2,3-dihydrobenzo[1,4]dioxine (Table
[1]
, entry 2): Yield: 74%; Yellow oil. 1H NMR (400 MHz, CDCl3): δ = 7.00 (d, J = 2.4 Hz, 1 H, ArH), 6.91 (dd, J = 8.8, 2.4 Hz, 1 H, ArH), 6.72 (d, J = 8.8 Hz, 1 H, ArH), 4.20 (br s, 4 H, CH
2CH
2). 13C NMR (100 MHz, CDCl3): δ = 144.4, 142.9, 124.3, 120.3, 118.6, 112.8, 64.3, 64.2. MS (EI): m/z = 214, 216 [M+·]. HRMS: m/z calcd for C8H7O2
79Br: 213.9629; found: 213.9628. 5-Bromobenzo[1,3]dioxole (Table
[1]
, entry 3): Yield: 71%; colourless oil. 1H NMR (400 MHz, CDCl3): δ = 6.92 (m, 2 H, ArH), 6.66 (d, J = 8.8 Hz, 1 H, ArH), 5.95 (s, 2 H, CH2).
13C NMR (100 MHz, CDCl3): δ = 148.6, 147.0, 124.3, 113.1, 112.3, 109.6, 101.7. MS (EI): m/z = 200, 202 [M+·]. HRMS: m/z calcd for C7H5O2
79Br: 199.9473; found: 199.9473. 4-Bromo-
N
,
N
-dimethylaniline (Table, entry 4): Yield: 73%; colourless oil. 1H NMR (400 MHz, CDCl3): δ = 7.27 (d, J = 8.7 Hz, 2 H, ArH), 6.55 (d, J = 8.7 Hz, 2 H, ArH), 2.89 (s, 6 H, CH3). 13C NMR (100 MHz, CDCl3): δ = 149.5, 131.7, 114.1, 108.5, 40.6. MS (ES): m/z = 200, 202 [MH+]. HRMS: m/z calcd for C8H11NBr: 200.0075; found: 200.0084. 2-Bromo-5-methylthiophene (Table
[1]
, entry 5): Yield: 88%; colourless oil. 1H NMR (400 MHz, CDCl3): δ = 6.83 (d, J = 3.7 Hz, 1 H, ArH), 6.51 (d, J = 3.7 Hz, 1 H, ArH), 2.42 (s, 3 H, CH3). 13C NMR (100 MHz, CDCl3): δ = 141.4, 129.6, 125.5, 108.5, 15.5. MS (EI): m/z = 176, 178 [M+·]. HRMS: m/z calcd for C5H5S79Br: 175.9295; found: 175.9336. 3-Bromo-benzo[
b
]thiophene (Table
[1]
, entry 6): Yield: 79%; colourless oil. 1H NMR (400 MHz, CDCl3): δ = 7.74-7.80 (m, 2 H, ArH), 7.40 (t, J = 7.4 Hz, 1 H, ArH), 7.35-7.32 (m, 2 H, ArH). 13C NMR (100 MHz, CDCl3): δ = 138.7, 137.6, 127.6, 125.1, 123.6, 123.2, 122.8, 107.8. MS (EI): m/z = 212, 214 [M+·]. HRMS: m/z calcd for C8H5S79Br: 211.9295; found: 211.9285. 4-Bromo-2,4,6-tri-
tert
-butylcyclohexa-2,5-dienone (Table
[1]
, entry 9): Yield: 87%; orange crystalline solid; mp 71-73 °C [lit.
[22]
80.5-81.5 °C]. IR (CH2Cl2): 1656, 1636 cm-1. 1H NMR (400 MHz, CDCl3):
δ = 6.92 (s, 2 H, ArH), 1.25 [s, 18 H, 2- and 6-C(CH3)3], 1.14 [s, 9 H, C(CH3)3)]. 13C NMR (100 MHz, CDCl3): δ = 189.0, 145.2, 139.9, 72.5, 40.0, 35.0, 29.4, 26.5. MS (CI+): 341, 343 [MH+]. HRMS: m/z calcd for C18H30O79Br: 341.1480; found: 341.1472. 5-Bromomethyl-γ-butyrolactone (Table, 1 entry 10): Yield: 89%; colourless oil. IR (thin film; NaCl): 1777 cm-1. 1H NMR (270 MHz, CDCl3): δ = 4.71 (m, 1 H, OCH), 3.51 (d, J = 5.1 Hz, 2 H, CH2Br), 2.70-2.32 (m, 3 H, CHHCH
2
), 2.17-1.96 (m, 1 H, CHH). 13C NMR (68 MHz, CDCl3): δ = 176.4, 78.0, 34.5, 28.5, 26.2. MS (CI+):
m/z = 196, 198 [M + NH4
+]. MS (CI-): 79, 81 [Br]. HRMS: m/z calcd for C5H11
79BrNO2: 195.9973; found: 195.9971. (2,3-Dibromopropoxy)benzene (Table
[1]
, entry 11): Yield: 87%; colourless oil. 1H NMR (270 MHz, CDCl3): δ = 7.37 (dt, J = 7.6, 0.9 Hz, 2 H, ArH), 7.07 (t, J = 7.6 Hz, 1 H, ArH), 6.99 (d, J = 7.6, 2 H, ArH), 4.49-4.32 (m, 3 H), 4.02-3.91 (m, 2 H). 13C NMR (68 MHz, CDCl3): δ = 158.1, 129.6, 121.9, 115.0, 69.2, 48.0, 33.1. MS (EI): m/z = 292, 294, 296 [M]. HRMS: m/z calcd for C5H11
79Br2NO2: 291.9098; found: 291.9092. Methyl 2,3-Dibromopropionate (Table
[1]
, entry 12): Yield: 80%; orange oil. 1H NMR (270 MHz, CDCl3):
δ = 4.40 (dd, J = 11.2, 4.4 Hz, 1 H), 3.87 (dd, J = 11.2, 9.9 Hz, 1 H), 3.79 (s, 3 H, CH3), 3.63 (dd, J = 9.9, 4.4 Hz, 1 H). 13C NMR (68 MHz, CDCl3): δ = 168.2, 53.5, 40.8, 29.7.
19 However, 1H NMR studies of LiBr-DIB in THF-d
8 failed to detect any new species: only PhI(OAc)2 and PhI could be observed.