LETTER
Strategy for Protecting Dihydroxyl Groups of Catechols
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2007/0027184A1, 2007; Chem. Abstr. 2007, 146, 206220
(24) General Cyclization Procedure
To EtOH (15 mL) were added in turn catechols 1 (5.0
mmol), K2CO3 (2.42 g, 17.5 mmol) and 1,3-dibromopropane
(0.66 mL, 6.5 mmol), then the mixture was heated at reflux
for 5 h. The resulting mixture was filtered and concentrated
to acquire the crude product, the purification of which by
column chromatography afforded the corresponding product
2 with PE–EtOAc (30:1, v/v) as eluents.
Representative Compound 2a
Colorless liquid, 0.69 g (92% yield). 1H NMR (400 MHz,
CDCl3): δ = 2.19 (quint, J = 5.6 Hz, 2 H, CH2), 4.22 (t, J =
5.6 Hz, 4 H, CH2), 6.90–6.95 (m, 2 H, Ar), 6.96–7.01 (m, 2
H, Ar) ppm. 13C NMR (100 MHz, CDCl3): δ = 31.9, 70.5 (2
C), 121.6 (2 C), 123.3 (2 C), 151.2 (2 C) ppm. ESI-HRMS:
m/z [M + H+] calcd for C9H11O2: 151.0759; found: 151.0757.
(25) General Deprotection Procedure
A solution of benzo[b]1,4-dioxepans 2 (3.0 mmol) in
benzene (10 mL) was treated by anhyd AlCl3 (1.20 g, 9.0
mmol), and the mixture was heated to reflux for specified
time. Then, the reaction mixture was quenched by sat. aq
NH4Cl (20 mL), and the aqueous phase was extracted with
EtOAc (3 × 10 mL). The combined organic phase was
washed by sat. brine (2 × 20 mL) and concentrated to
provide the crude product, the purification of which by
column chromatography afforded the corresponding product
1 with PE–EtOAc (10:1, v/v) as eluents.
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(27) Synthetic Procedures for Compounds 4–6
Compound 4
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Bromine (0.17 mL, 3.4 mmol, dissolved in 2 mL EtOH) was
added dropwise to a stirred solution of 3 (0.50 g, 2.6 mmol)
in EtOH (8 mL), and the mixture was stirred at r.t. for 1 h.
Then, the solvent was removed to get the crude product, the
purification of which by column chromatography afforded
the pure product 4 with PE–CH2Cl2 (15:1, v/v) as eluents;
white solid; mp 72–74 °C; 0.62 g (88% yield). 1H NMR (400
MHz, CDCl3): δ = 2.25 (quint, J = 5.6 Hz, 2 H, CH2), 4.28
(t, J = 5.6 Hz, 2 H, CH2), 4.34 (t, J = 5.6 Hz, 2 H, CH2), 4.37
(s, 2 H, CH2), 7.00 (d, J = 8.4 Hz, 1 H, Ar), 7.57 (d, J = 8.4
Hz, 1 H, Ar), 7.60 (s, 1 H, Ar) ppm. 13C NMR (100 MHz,
CDCl3): δ = 30.79, 30.81, 70.2, 70.4, 121.6, 122.7, 124.7,
129.1, 150.6, 156.0, 189.8 ppm. ESI-HRMS: m/z [M + H+]
calcd for C11H12O3Br: 270.9970; found: 270.9975.
Compound 5
A solution of 4 (0.54 g, 2.0 mmol) and thiourea (0.18 g, 2.4
mmol) in absolute EtOH (12 mL) was refluxed for 2 h. After
removal of the solvent, the residue was treated with aq
NaOH (1 mol/L, 10 mL), and extracted with EtOAc (3 × 10
mL). The combined organic phase was concentrated to
provide the crude product, the purification of which by
column chromatography afforded the pure product 5 with
PE–EtOAc (4:1, v/v) as eluents; light yellow solid; mp 174–
177 °C, 0.46 g (92% yield). 1H NMR (400 MHz, CDCl3): δ
= 2.20 (quint, J = 5.2 Hz, 2 H, CH2), 4.22 (t, J = 5.2 Hz, 4 H,
CH2), 5.05 (s, 2 H, NH2), 6.60 (s, 1 H, thiazole), 6.97 (d, J =
8.4 Hz, 1 H, Ar), 7.34 (d, J = 8.4 Hz, 1 H, Ar), 7.40 (s, 1 H,
Ar) ppm. 13C NMR (100 MHz, CDCl3): δ = 31.8, 70.6 (2 C),
102.1, 119.3, 121.1, 121.7, 130.3, 150.5, 151.0, 151.2,
167.1. ESI-HRMS: m/z [M + H+] calcd for C12H13N2O2S:
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Synlett 2013, 24, 741–746