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6g For a related electrochemical
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Aulenta F.
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8a For
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9
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10 Compound 9 was
synthesized in a two-step procedure: 1. ethyl isobutyrate, phenethyl
iodide, LDA, HMPA, THF, -78 ˚C;
2. TMSCH2Li, pentane, 0 ˚C then MeOH,
55% (2 steps). For the second step, see: Demuth M.
Helv. Chim. Acta
1978,
61:
3136
11 Conjugate addition of a benzyl cuprate
to mesityl oxide furnished compound 11a in
low yield: BnMgCl, CuCN, BF3˙OEt2,
mesityl oxide, Et2O, -78 ˚C,
15%.
12
Mahmud SA.
Ansell MF.
J. Chem. Soc., Perkin
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1973,
2789
13 The samarium ketyl is very likely
in equilibrium with ketone 9 which was
re-isolated. Reduction of the ketyl and subsequent protonation furnishes 10.
14
General Procedure
for Samarium Diiodide Induced Cyclizations of Aryl Ketones
HMPA
(18 equiv) was added to a previously prepared stock solution of
SmI2 in THF (0.1 M, 3 equiv) under argon, and the solution
was stirred for 20 min. During this time the solution turned from
dark blue to dark violet. In a separate flask, the substrate (1
equiv) and t-BuOH (2 equiv) were dissolved
in THF (10 mL) under argon. Argon was bubbled through the solution
for 20 min. The substrate solution was then transferred with a syringe
to the samarium diiodide solution. The mixture was stirred at r.t.
until the color changed from violet to grey. Saturated aq NaHCO3 solution was
added, the organic layer was separated, and the aqueous layer was
extracted with Et2O (3×). The combined organic layers
were washed with H2O and brine, dried with MgSO4, and
the solvent was removed under reduced pressure to give the crude
product, which still contained small amounts of HMPA. Flash chromatography
on Al2O3 (activity grade 3) yielded the cyclization
products.
15
Cyclization of
11a
According to the general procedure, the SmI2 solution
in THF (15.8 mL, 1.58 mmol), HMPA (1.66 mL, 9.47 mmol), 11a (0.100 g, 0.53 mmol), and t-BuOH (0.078 g, 1.05 mmol) afforded
after purification by flash chromatography (hexane-EtOAc,
9:1) compounds 12a and 13a as
a 83:17 mixture in 75% yield (76 mg).
Spectroscopic
Data for (1
S
*,8a
S
*)-1,3,3-Trimethyl-1,2,3,4,8,8a-hexahydronaphthalen-1-ol (12a)
¹H NMR
(700 MHz, CDCl3): δ = 0.93,
0.96. 1.26* (3 s, 3 H each, CH3), 1.28* (br
s, 1 H, OH), 1.50 (d, J = 13.4
Hz, 1 H, 2-H), 1.62 (dd, J = 2.2,
13.4 Hz, 1 H, 2-H), 1.88 (dd, J = 2.2, 12.6
Hz, 1 H, 4-H), 2.03 (d, J = 12.6
Hz, 1 H, 4-H), 2.23 (dd, J = 3.5,
13.0 Hz, 1 H, 8a-H), 2.49 (tdd, J = 3.1,
13.0, 19.5 Hz, 1 H, 8-H), 2.57 (m, 1 H, 8-H), 5.54 (tddd, J = 0.9, 3.1, 8.6,
9.5 Hz, 1 H, 7-H), 5.58-5.60 (m, 1 H, 5-H), 5.67 (dddd, J = 1.3, 3.1,
5.4, 9.5 Hz, 1 H, 6-H) ppm; * overlapping signals. ¹³C
NMR (176 MHz, CDCl3): δ = 22.4
(t, C-8), 23.2, 26.6 (2 q, CH3), 32.8 (s, C-3) 33.9 (q,
CH3), 46.9 (d, C-8a), 48.7 (t, C-4), 55.9 (t, C-2), 74.9
(s, C-1), 118.9, 122.2, 123.5 (3 d, C-5, C-6, C-7), 136.5 (s, C-4a)
ppm.
Spectroscopic Data for (1
S
*,8a
S
*)-1,3,3-Trimethyl-1,2,3,4,6,8a-hexahydronaphthalen-1-ol (13a)
¹H NMR
(700 MHz, CDCl3): δ = 0.90,
0.98, 1.12 (3 s, 3 H each, CH3), 1.52 (br s, 1 H, OH),
1.59 (d, J = 13.2
Hz, 1 H, 2-H), 1.68 (dd, J = 2.2,
13.2 Hz, 1 H, 2-H), 1.87, 1.92 (AB part of an ABX system, J
AB = 13.0
Hz, J
BX = 2.2
Hz, 1 H each, 4-H), 2.62 (mc, 1 H, 8a-H), 2.67-2.71
(m, 2 H, 6-H), 5.47 (X part, mc, 1 H, 5-H), 5.85 (mc,
2 H, 7-H, 8-H) ppm. ¹³C NMR (176 MHz,
CDCl3): δ = 24.9,
26.2 (2 q, CH3), 27.0 (t, C-6), 32.2 (s, C-3), 33.9 (q,
CH3), 48.7 (t, C-4), 49.0 (d, C-8a), 55.3 (t, C-2), 74.5
(s, C-1), 120.1 (d, C-5), 124.3, 125.6 (2 d, C-7, C-8), 141.6 (s,
C-4a) ppm. Data from mixture: IR (film): ν = 3365
(OH), 2950-2830 (CH), 1630 (C=C) cm-¹.
HRMS (EI, 80 eV, 60 ˚C): m/z calcd
for C13H20O [M]+:
192.1514; found: 192.1513. Anal. Calcd for C13H20O
(192.1): C, 81.20; H, 10.48; found: C, 80.93; H, 10.31.
Cyclization of 14
According to
the general procedure, the SmI2 solution in THF (15.8
mL, 1.58 mmol), HMPA (1.66 mL, 9.47 mmol), 14 (0.100
g, 0.53 mmol), and t-BuOH (0.078 g, 1.05
mmol) afforded after purification by flash chromatography (hexane-EtOAc,
9:1) compounds 15, 16,
and 17 as a 74:19:7 mixture in 70% yield
(71 mg). Separation by HPLC yielded pure samples.
Analytical Data for (1
S
*,8a
S
*)-1,4,4-Trimethyl-1,2,3,4,8,8a-hexahydronaphthalen-1-ol (15)
Colorless solid; mp 50-52 ˚C. ¹H
NMR (700 MHz, CDCl3): δ = 1.09,
1.14, 1.17 (3 s, 3 H each, CH3), 1.35 (dt, J = 4.5, 13.6
Hz, 1 H, 3-H), 1.46* (br s, 1 H, OH), 1.47* (ddd, J = 2.9, 4.4,
13.6 Hz, 1 H, 3-H), 1.60 (ddd, J = 2.9,
4.4, 13.6 Hz, 1 H, 2-H), 1.77 (dt, J = 4.5,
13.6 Hz, 1 H, 2-H), 2.47 (tdd, J = 3.1,
13.8, 20.0 Hz, 1 H, 8-H), 2.61-2.67 (m, 2 H, 8-H, 8a-H),
5.52 (dddd, J = 0.8,
3.3, 5.0, 9.0 Hz, 1 H, 7-H), 5.64 (br d, J = 5.7
Hz, 1 H, 5-H), 5.69 (dddd, J = 1.4,
3.0, 5.7, 9.0 Hz, 1 H, 6-H) ppm; * overlapping signals. ¹³C
NMR (176 MHz, CDCl3): δ = 20.4
(q, CH3), 22.7 (t, C-8), 26.2, 28.5 (2 q, CH3),
35.9 (s, C-4), 38.5, 38.8 (2 t, C-3, C-2), 42.4 (d, C-8a), 75.6
(s, C-1), 115.2 (d, C-5), 122.2 (d, C-6), 123.1 (d, C-7), 145.0
(s, C-4a) ppm. IR (film): ν = 3375
(OH), 2970-2865 (=CH, CH), 1665 (C=C) cm-¹.
Analytical Data for (1
S
*,8a
S
*)-1,4,4-Trimethyl-1,2,3,4,6,8a-hexahydronaphthalen-1-ol (16)
¹H NMR
(700 MHz, CDCl3): δ = 1.03,
1.08. 1.09 (3 s, 3 H each, CH3), 1.32 (dt, J = 4.2, 13.8
Hz, 1 H, 3-H), 1.43 (ddd, J = 2.9,
4.4, 13.8 Hz, 1 H, 3-H), 1.55 (br s, 1 H, OH), 1.63 (ddd, J = 2.9, 4.2,
12.9 Hz, 1 H, 2-H), 1.86 (ddd, J = 2.9,
4.2, 12.9 Hz, 1 H, 2-H), 2.66-2.70 (m, 2 H, 6-H), 2.97-3.01
(m, 1 H, 8a-H), 5.47-5.51 (m, 1 H, 5-H), 5.81-5.85
(m, 1 H, 7-H), 5.87 (tdd, J = 1.8,
3.3, 10.2 Hz, 1 H, 8-H) ppm. ¹³C NMR (176
MHz, CDCl3): δ = 21.5,
25.7 (2 q, CH3), 27.1 (t, C-6), 28.7 (q, CH3),
34.4 (s, C-4), 37.8, 38.0 (2 t, C-2, C-3), 44.7 (d, C-8a), 71.0
(s, C-1), 116.2 (d, C-5), 124.5, 125.4 (2 d,
C-8, C-7),
142.2 (s, C-4a) ppm. IR (film): ν = 3410
(OH), 2960-2810 (=CH, CH), 1650 (C=C)
cm-¹. HRMS (ESI-TOF-MS): m/z calcd for C13H20ONa [M + Na]+:
215.1406; found: 215.1405.
Analytical
Data for 1,4,4-Trimethyl-1,2,3,4-tetrahydronaphthalen-1-ol (17)
Colorless solid; mp 68-70 ˚C. ¹H
NMR (700 MHz, CDCl3): δ = 1.30,
1.31, 1.55 (3 s, 3 H each, CH3), 1.68 (br s, 1 H, OH),
1.71-1.83, 1.96-1.99 (2 m, 4 H, 2-H, 3-H), 7.18-7.24 (m,
2 H, Ar), 7.29-7.31 (m, 1 H, Ar), 7.58-7.59 (m,
1 H, Ar) ppm. ¹³C NMR (176 MHz, CDCl3): δ = 30.8,
31.5, 31.7 (3 q, CH3), 34.06 (s, C-4), 35.9, 36.1 (2
t, CH2), 71.0 (s, C-1), 126.0, 126.1, 126.4, 127.4 (4
d, Ar), 142.0, 144.7 (2 s, Ar) ppm. IR (film): ν = 3385
(OH), 2960-2860 (=CH, CH), 1660 (C=C)
cm-¹. HRMS (ESI-TOF-MS): m/z calcd for C13H18ONa [M + Na]+:
213.1250; found: 213.1250.
16 At the moment it is more likely that
the isolation of isomeric mixtures is the result of an unselective
kinetically controlled protonation. Since equilibration experiments
with the products isolated are so far not fully conclusive, further investigation
of this problem is required.