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General Procedure
for the Synthesis of 3-Bromo-2
H
-chromene Derivatives 2a-l
To
a stirred mixture of the aryl propargyl ether 1a-l (1 mmol) in AcOH, Pd(OAc)2 (5
mol%), LiBr (1 mmol), and CuBr2 (2.5 mmol) were
added at r.t. The reaction mixture was stirred until completion
of the reaction as monitored by TLC. A sat. solution of NaHCO3 was
then added to neutralize the reaction mixture, which was then extracted with
EtOAc (3 × 10 mL). The organic layer
was dried over anhyd Na2SO4. Removal of the
solvent under reduced pressure gave the crude product, which was
purified by column chromatography on silica gel using hexane as
eluent to afford the pure product.
<A NAME="RG08909ST-16">16</A>
3-Bromo-4-ethyl-2
H
-chromene (2a,
Table 1, Entry 1)
Colorless oily liquid. IR (KBr): νmax = 3062,
2966, 2851, 2354, 1629, 1467 cm-¹.¹H
NMR (500 MHz, CDCl3): δ = 1.14 (t,
3 H, J = 7.5
Hz), 2.65 (q, 2 H, J = 7.5
Hz), 4.86 (s, 2 H), 6.86 (d, 1 H, J = 8.0
Hz), 6.95 (t, 1 H, J = 7.5
Hz), 7.16 (t, 1 H, J = 7.5
Hz), 7.22 (d, 1 H, J = 8.0
Hz). ¹³C NMR (125 MHz, CDCl3): δ = 12.4,
23.8, 70.8, 112.9, 116.3, 121.9, 122.6, 123.6, 129.1, 134.6, 153.3.
ESI-MS: m/z = 239 [M+ + 1],
241 [M+ + 3]. Anal.
Calcd (%) for C11H11BrO: C, 55.26; H,
4.65. Found: C, 55.31; H, 4.71.
<A NAME="RG08909ST-17">17</A>
3-Bromo-4-ethyl-2
H
-benzo[
h
]chromene
(2f, Table 2, Entry 1)
Colorless oily liquid. IR (KBr): νmax = 3062,
2956, 1738, 1642, 1561, 1466 cm-¹.¹H
NMR (500 MHz, CDCl3): δ = 1.96 (t,
3 H, J = 7.7
Hz), 2.75 (q, 2 H, J = 7.7
Hz), 5.06 (s, 2 H), 7.38 (d, 1 H, J = 8.2
Hz), 7.45-7.49 (m, 3 H), 7.76-7.8 (m, 1 H), 8.17-8.19
(m, 1 H). ¹³C NMR (125 MHz, CDCl3): δ = 12.6,
24.1, 71.3, 110.7, 117.3, 121.2, 121.4, 122.2, 124.6, 125.9, 126.8,
127.6, 134.0, 135.3, 149.1. ESI-MS: m/z = 289 [M+ + 1],
291 [M+ + 3]. Anal.
Calcd (%) for C15H13BrO: C, 62.30;
H, 4.53. Found: C, 62.21; H, 4.65.
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