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11
General Procedure
and Selected Characterization Data
To a stirred solution
of 3 (0.3 mmol) in CH2Cl2 (3
mL) at 0 ˚C was added BF3˙OEt2 (0.33
mmol). After 10 min, the resulting solution was warmed to r.t. and
stirred for 90 min (excepted in the case of 3d).
The reaction mixture was quenched with sat. aq NaHCO3 (1
mL), and the aqueous phase was extracted with Et2O (2 × 2
mL). The combined organic phases were washed with brine, dried over
MgSO4, filtrated, and concentrated under reduced pressure. Compounds 4 were purified by flash chromatography
on silica gel (210-400 mesh).
Compound 4d was obtained as a colorless oil (95%). [α]D
²5 +33.5
(c 1.75, CH2Cl2). ¹H
NMR (300 MHz, CDCl3): δ = 1.03
(s, 9 H), 1.91-1.97 (m, 1 H), 2.33-2.42 (m, 1
H), 4.26 (d, 1 H, J = 8.4
Hz), 4.44 (d, 1 H, J = 8.8
Hz), 4.47 (d, 1 H, J = 4.9
Hz), 5.50-5.52 (m, 1 H), 5.60-5.63 (m, 1 H), 5.98-6.04
(m, 1 H), 7.20-7.28 (m, 7 H), 7.35-7.49 (m, 6
H), 7.66-7.71 (m, 2 H). ¹³C
NMR (75 MHz, CDCl3): δ = 19.4, 26.9,
33.8, 72.0, 75.0, 88.7, 100.9, 124.3, 127.4, 127.5, 127.6, 127.7,
128.0, 128.9, 129.7, 129.8, 133.0, 134.0, 135.9, 136.0, 141.4. Anal.
Calcd for C29H32O3Si: C, 76.28; H,
7.06. Found: C, 76.35; H, 7.01.
12 Compound 8 was
obtained as colorless oil (87%). [α]D
²5 +20.3
(c 1.30, CH2Cl2). ¹H
NMR (300 MHz, CDCl3): δ = 1.03
(s, 9 H), 1.45-1.88 (m, 4 H), 2.29 (br s, 1 H), 3.60-3.63
(m, 1 H), 4.04 (d, 1 H, J = 7.3
Hz), 4.20-4.25 (m, 1 H), 4.49 (d, 1 H, J = 7.3
Hz), 5.32 (br s, 1 H), 7.21-7.33 (m, 7 H), 7.35-7.48
(m, 6 H), 7.61-7.69 (m, 2 H). ¹³C
NMR (75 MHz, CDCl3): δ = 19.4,
23.8, 26.8, 26.9, 66.7, 76.1, 77.2, 78.9, 81.5, 102.5, 127.4, 127.6,
127.8, 128.1, 129.6, 129.8, 133.1, 133.8, 135.9, 136.0, 140.9. Anal.
Calcd for C29H34O4Si: C, 73.38;
H, 7.22. Found: C, 73.37; H, 7.11.
15 The ee was measured by GC analysis
using a chiral stationary phase (Varian WCOT Fused Silica 25 × 0.25
mm coated CP Chirasil-dex CB DF = 0.25).
19 1-Phenylpropan-1-one can be obtained
from the corresponding allylic alcohol in 97% yield with
only 2 mol% of [RuCp*(MeCN)3][PF6] in
toluene at r.t. These new conditions represent an improvement of
the previously described process with this catalyst.
20
Characterization
Data for Key Synthetic Intermediates
Compound 3e was obtained from 1 in
70% yield as a colorless oil. [α]D
²5 +72
(c 0.59, CH2Cl2). ¹H
NMR (300 MHz, CDCl3): δ = 1.18-1.25
(m, 6 H), 2.19-2.22 (m, 2 H), 2.72 (br s, 1 H), 3.53 (dq,
1 H, J = 7.1,
9.3 Hz), 3.69-3.72 (m, 1 H), 3.96 (dq, 1 H, J = 7.1, 9.3
Hz), 3.98-4.03 (m, 1 H), 4.72 (dd, 1 H, J = 4.8,
6.1 Hz), 5.60-5.63 (m, 1 H), 5.78-5.80 (m, 1 H). ¹³C
NMR (75 MHz, CDCl3): δ = 15.2,
18.6, 31.1, 64.4, 69.6, 78.8, 98.5, 124.9, 126.1. HRMS (EI): m/z [M -˙OCH2CH3]+ calcd
for C7H11O2: 127.0759; found: 127.0755.
Compound 12 was obtained as colorless oil (mixture
of diastereomers, 63%). ¹H NMR (300
MHz, CDCl3): δ = 1.20 (d,
3 H, J = 5.9
Hz), 1.35-1.70 (m, 6 H), 1.81 (br s, 1 H), 2.68 (br s,
1 H), 3.40-3.43 (m, 2 H), 4.09-4.12 (m, 1 H),
4.43 (d, 1 H, J = 11.5
Hz), 4.68 (d, 1 H, J = 11.5
Hz), 5.11 (dd, 1 H, J = 1.2,
10.4 Hz), 5.23 (d, 1 H, J = 17.2
Hz), 5.88 (ddd, 1 H, J = 6.2,
10.4, 17.2 Hz), 7.26-7.43 (m, 5 H). ¹³C
NMR (75 MHz, CDCl3): δ = 15.5,
21.3, 21.4, 32.5, 32.6, 36.9, 71.0, 73.0, 73.1, 74.8, 74.9, 78.3,
78.4, 114.5, 114.6, 127.7, 127.8, 128.5, 138.3, 141.1, 141.2. ESI-HRMS: m/z [M + Na]+ calcd for
C16H24O3Na: 287.1623; found: 287.1623.
(+)-Iso-exo-brevicomin was obtained as a colorless
oil (highly volatile, 60%): [α]D
²5 +53
(c 0.3, CHCl3); lit.¹4d [α]D +54
(c 0.5, CHCl3). ¹H
NMR (300 MHz, CDCl3): δ = 0.96
(t, 3 H, J = 7.9
Hz), 1.18 (d, 3 H, J = 6.5
Hz), 1.43-1.95 (m, 8 H), 4.06 (br s, 1 H), 4.22 (q, 1 H, J = 6.5 Hz). ¹³C
NMR (75 MHz, CDCl3): δ = 7.3,
17.1, 21.6, 28.0, 30.6, 33.5, 75.5, 79.9, 109.5. Anal. Calcd for
C9H16O2: C, 69.19; H, 10.32. Found:
C, 69.27; H, 10.41.