References and Notes
1 Current address: Graduate School
of Medicine and Pharmaceutical Sciences, University of Toyama, 2630 Sugitani,
Toyama 930-0194, Japan.
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8 The relative stereochemistry was
determined after derivatization to β-lactam 18.
The absolute stereochemistry was tentatively assigned according
to the Qin’s proposed transition state (ref. 7).
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10 The ee was determined by HPLC (Daicel
CHIRALCEL
OD-H, flow rate: 0.50 mL/min, hexane-i-PrOH = 80:20, t
R = 10.0, 13.1 min).
11 The stereochemistry was tentatively
assigned as described based on the general reactivity of 4-substituted
azetidine 2,3-dione. For a typical example, see: Kant J.
Schwartz WS.
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Gao Q.
Huang S.
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12 We found that the hydroxyl group
should be activated as a mesylate for the smooth and high-yielding
process. The O-methylated substrate has a low reactivity, and degradation
of the starting material was observed. On the contrary, The O-triflated
substrate was found to be unstable.
13
Procedure for
the Intramolecular Friedel-Crafts Alkylation: A 30-mL
round-bottomed flask equipped with a magnetic stirrer bar and an
inlet adapter with three-way stopcock was charged with tertiary
alcohol 21 (740 mg, 1.62 mmol). The flask
was evacuated and backfilled with argon gas. To the flask was added
anhyd CH2Cl2 (6.0 mL), and the resulting solution
was cooled to 0 ˚C. To the solution were added Et3N
(0.70 mL, 5.0 mmol) and methanesulfonyl chloride (0.25 mL, 3.2 mmol)
at 0 ˚C, respectively. The reaction mixture was then warmed
to r.t. and stirred for 8 h, after which time TLC (hexanes-EtOAc,
1:1) indicated complete consumption of the starting alcohol. The
reaction was quenched with sat. aq NH4Cl, and the mixture
was extracted with CH2Cl2 (3 ×).
The combined organic extracts were washed with brine, dried over
MgSO4, and filtered. The filtrate was concentrated under
reduced pressure to give a crude mesylate (1.1 g), which was used
for the next reaction.
A 30-mL round-bottomed flask equipped
with a magnetic stirrer bar and an inlet adapter with three-way
stopcock was charged with the crude mesylate (1.1 g). The flask
was evacuated and backfilled with argon gas. To the flask was added
anhyd MeCN (20 mL), and the resulting solution was cooled to -40 ˚C.
To the solution was added TfOH (0.70 mL, 7.9 mmol) at -40 ˚C.
The reaction mixture was warmed to r.t. and stirred for 3 h, after
which time TLC (hexanes-EtOAc, 3:2) indicated complete
consumption of the starting mesylate. After cooling to 0 ˚C,
the reaction mixture was treated with sat. aq NaHCO3,
and the mixture was extracted with EtOAc (3 ×). The combined
organic extracts were concentrated under reduced pressure to give
the crude material, which was purified by column chromatography
on silica gel to provide the title compound 23 (495
mg, 1.19 mmol, 74% over 2 steps) as a pale yellow amorphous
solid; [α]D
²³ -67.8
(c = 1.15, CHCl3).
IR (neat): 2939, 2835, 1747, 1601, 1489, 1456, 1339, 1151, 1078,
1047, 910, 733, 698 cm-¹. ¹H
NMR (400 MHz, CDCl3): δ = 7.20-7.37
(m, 6 H), 6.88-6.95 (m, 2 H), 6.76-6.81 (m, 1
H), 6.31-6.35 (m, 2 H), 4.66 (d, 1 H, J = 15.2
Hz), 4.23 (d, 1 H, J = 15.2
Hz), 4.02 (d, 1 H, J = 6.4 Hz),
3.79 (s, 3 H), 3.76 (s, 3 H), 3.63 (s, 3 H), 2.99 (dd, 1 H, J = 17.6, 6.4 Hz), 2.87 (d,
1 H, J = 17.6 Hz). ¹³C
NMR (100 MHz, CDCl3): δ = 169.8, 161.9,
159.5, 158.3, 144.9, 139.0, 136.0, 129.2, 128.7, 128.1, 127.6, 120.8, 119.1,
112.5, 112.4, 102.0, 98.1, 75.4, 65.3, 55.7, 55.5, 55.1, 43.7,
32.8. HRMS (ESI+): m/z [M + Na+] calcd
for C26H25NO4Na: 438.1681; found:
438.1674.
14a
D’Annibale A.
Pesce A.
Resta S.
Trogolo C.
Tetrahedron
1997,
53:
13129
14b
Bhalla A.
Madan S.
Venugopalan P.
Bari SS.
Tetrahedron
2006,
62:
5054
15
Procedure for
the Intramolecular McMurry Coupling Reaction: A 10-mL test
tube equipped with a magnetic stirrer bar and an inlet adapter with
three-way stopcock was charged with Zn/Cu (6.2 mg, 95 µmol).
The flask was flame-dried and backfilled with argon gas. To the
flask was added degassed anyhd 1,2-dimethoxyethane (0.18 mL), and
the resulting suspension was cooled to 0 ˚C. To the suspension was
added TiCl4 (4.0 µL, 36 µmol), and
the mixture was heated at 90 ˚C for 1.5 h. After the flask
was cooled to 0 ˚C, substrate 6 (2.0
mg, 3.5 µmol) in 1,2-dimethoxyethane (50 µL) was
added to the flask. The reaction mixture was warmed to r.t. over
30 min and then heated at 90 ˚C for 2 h, after which time
TLC (hexanes-EtOAc, 1:1) indicated complete consumption
of the starting material. After cooling to r.t., the mixture was
diluted with EtOAc and filtered through a celite pad. The filtrate
was concentrated under reduced pressure to give the crude material,
which was purified by preparative TLC providing the title compound 5 (0.42 mg, 0.78 µmol, 22%)
as a colorless film. IR (neat): 3302, 2934, 1674, 1599, 1470, 1337,
1290, 1207, 1150, 754 cm-¹. ¹H
NMR (400 MHz, CDCl3): δ = 7.45 (d,
1 H, J = 8.8 Hz), 7.21-7.26
(m, 1 H), 6.91 (d, 1 H, J = 2.4
Hz), 6.78-6.86 (m, 3 H), 6.75 (dd, 1 H, J = 8.8,
3.2 Hz), 6.66 (s, 1 H), 6.48 (d, 1 H, J = 2.0
Hz), 6.36 (d, 1 H, J = 2.0 Hz),
5.66 (s, 1 H), 4.14-4.21 (m, 1 H), 3.83 (s, 3 H), 3.79
(s, 3 H), 3.76 (s, 3 H), 3.59 (s, 3 H), 3.33 (dd, 1 H, J = 16.0, 7.6 Hz), 3.08-3.16
(m, 1 H). ¹³C NMR (125 MHz, CDCl3): δ = 163.4,
161.7, 159.8, 158.8, 157.2, 145.1, 143.9, 141.1, 138.9, 134.0, 133.0, 129.3,
122.3, 119.1, 117.2, 115.0, 114.4, 112.9, 112.0, 101.2, 98.3, 77.2,
64.6, 55.6, 55.5, 55.2, 55.1, 41.2. HRMS (ESI+): m/z [M + Na+] calcd
for C28H26
79BrNO5Na: 558.0892;
found: 558.0873.
16 Reduction of the amide is reported
using a similar compound by Weinreb (ref. 3d).
17 Chemical shifts of ¹H
NMR and ¹³C NMR of 5 were
in excellent agreement with those of the analogous compound reported
by Weinreb (ref. 3d).
