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Typical Procedure
for the Conversion of 4a into Compound 6
Refluxing
a suspension of enamide 4a (0.4 mmol, 111
mg) in deionized H2O (12 mL) for 4 h under argon protection gave
rise to a homogeneous solution. After addition of brine (30 mL),
the mixture was extracted with EtOAc (3 × 20
mL). The organic layer was dried with anhyd Na2SO4,
filtered, and concentrated under vacuum. The residue was subjected to
chromatography using a silica gel (200-300 mesh) column
eluting with a mixture of PE and EtOAc (1:1) as mobile phase to
give product 6.
Mp 130-132 ˚C.
IR (KBr): ν = 3307, 1637 cm-¹. ¹H
NMR (300 MHz, CDCl3, 300 K): δ = 7.23-7.98
(m, 10 H), 6.26 (s, 1 H), 4.38 (dd, J = 3.9,
5.2 Hz, 1 H), 3.73-3.85 (m, 2 H), 3.41-3.47 (m,
1 H), 3.29 (d, J = 5.6
Hz, 1 H), 2.71 (d, J = 2.7 Hz,
3 H). ¹³C NMR (75 MHz, CDCl3,
300 K): δ = 199.5, 172.8, 139.2, 136.8, 133.4,
128.76, 128.7, 128.4, 128.2, 127.3, 73.6, 44.8, 40.7, 25.7. ESI-MS:
298 (52) [M + 1]+, 320
(100) [M + Na]+.
Anal. Calcd for C18H19NO3: C, 72.71; H,
6.44; N, 4.71. Found: C, 72.94; H, 6.59; N, 4.86.
<A NAME="RW32710ST-13">13</A>
General Procedure
for the Synthesis of Compounds 5 and 8
To a solution
of 4 or 7 (0.4
mmol) in dry MeCN (12 mL) was added PTSA (0.08 mmol, 14 mg) while
stirring at 0 ˚C. The mixture was then kept stirring
until the starting material was completely consumed. Water (100
mL) was added, and the mixture was extracted with EtOAc (3 × 50
mL). The organic layer was dried with anhyd MgSO4 and
concentrated. The residue was subjected to a silica gel (200-300
mesh) column eluted with a mixture of PE and EtOAc (3:1) to afford
pure 5 or 8.
Selected Data for Compound 5a
Mp
143-145 ˚C. IR (KBr): ν = 3442,
1668 cm-¹. ¹H NMR (300
MHz, CDCl3, 300 K): δ = 7.25-7.40
(m, 10 H), 5.35 (d, J = 2.4
Hz, 1 H), 4.38 (dd, J = 1.0,
13.7 Hz, 1 H), 3.88 (d, J = 1.8
Hz, 1 H), 3.78 (dd, J = 2.4,
13.7 Hz, 1 H), 3.04 (s, 3 H). ¹³C NMR
(75 MHz, CDCl3, 300 K): δ = 172.9,
141.6, 140.6, 135.0, 128.9, 128.7, 128.66, 128.0, 127.7, 127.3,
113.3, 71.3, 45.8, 32.7. ESI-MS: m/z = 280
(26) [M + 1]+, 302
(100) [M + Na]+.
Anal. Calcd for C18H17NO2: C, 77.40;
H, 6.13; N, 5.01. Found: C, 77.25; H, 6.39; N, 4.94.