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E. Palombo et al. / Tetrahedron Letters 44 (2003) 6463–6464
Scheme 1. Reagents and conditions. (a) DIBAL, toluene, −70°C, 95%; (b) Ph3P+CH2OMeCl−, n-BuLi, THF, rt, 82%; (c) i. NaH,
CS2, MeI, rt, THF; ii. HSnBu3, cat. AIBN, toluene, reflux, 90% (two steps); (d) 1 M HCl/THF: 1/2, rt, THF, 79%; (e)
Ph3PꢀC(CH3)CHO, toluene, reflux, 90%; (f) Ph3P+MeI−, tert-BuOK, toluene, rt, 92%; (g) 3-bromofuran, n-BuLi, THF, −78°C,
,
80%; (h) NMO, cat. (n-Pr)4NRuO4, 4 A MS, CH2Cl2, rt, 70%.
and 13C NMR) of synthetic (+)-1 matched those
reported for natural 11,7 and the specific rotation was
comparable in magnitude and the same in sign, [h]D25
+10 (CHCl3)/lit.1 [h]D20 +9.5 (CDCl3), indicating the
synthesis of the natural enantiomer. The (S)-configura-
tion was therefore assigned to natural dehydro-b-mono-
cyclonerolidol (+)-1.
6. Audran, G.; Uttaro, J.-P.; Monti, H. Synlett 2002, 1261–
1264.
7. All new compounds were fully characterized spectroscop-
ically and had satisfactory microanalyses. Selected data:
Compound (+)-3, [h]D25 +31 (c 1.0, CHCl3), lit.2 [h]D20 +29.0
1
(c 0.35, CH2Cl2); H NMR (300 MHz, CDCl3): l 9.62 (t,
1H, J=2.3 Hz), 4.79 (s, 1H), 4.50 (s, 1H), 2.52–2.40 (m,
3H), 2.18 (dt, 1H, J=13.2, 5.8 Hz), 2.03 (ddd, 1H, J=13.2,
8.0, 5.5 Hz), 1.65–1.22 (m, 4H), 0.96 (s, 3H), 0.77 (s, 3H);
13C NMR (75 MHz, CDCl3): l 203.2, 148.5, 109.2, 47.8,
41.5, 38.5, 34.9, 34.4, 28.8, 23.5, 23.4. Anal. calcd for
C11H18O: C, 79.47; H, 10.91. Found: C, 79.31; H, 10.94.
Compound (+)-9, [h]D25 +20 (c 1.0, CHCl3); 1H NMR (300
MHz, CDCl3): l 9.32 (s, 1H), 6.40 (tq, 1H, J=7.5, 1.2 Hz),
4.77 (br s, 1H), 4.47 (br s, 1H), 2.55–2.34 (m, 2H), 2.15–1.90
(m, 3H), 1.72 (d, 3H, J=1.0 Hz), 1.58–1.43 (m, 3H),
1.34–1.23 (m, 1H), 0.96 (s, 3H), 0.85 (s, 3H); 13C NMR (75
MHz, CDCl3): l 195.2, 155.3, 148.3, 138.9, 109.5, 53.3,
37.3, 35.1, 33.4, 28.6, 26.4, 24.8, 23.5, 9.27. Anal. calcd for
C14H22O: C, 81.50; H, 10.75. Found: C, 81.77; H, 10.72.
Compound (+)-1, [h]D25 +10 (c 2.0, CHCl3), lit.1 [h]2D0 +9.5
(c 10.1, CDCl3); 1H NMR (300 MHz, CDCl3): l 6.35 (dd,
1H, J=17.4, 10.8 Hz), 5.40 (t, 1H, J=6.8 Hz), 5.03 (d, 1H,
J=17.3 Hz), 4.88 (d, 1H, J=10.8 Hz), 4.75 (s, 1H), 4.49
(d, 1H, J=1.9 Hz), 2.35 (ddd, 1H, J=15.5, 6.4, 4.0 Hz),
1.97 (m, 1H), 1.82 (dd, 1H, J=11.1, 4.0 Hz), 1.73 (s, 3H),
1.55–1.42 (m, 3H), 1.36–1.22 (m, 1H), 0.95 (s, 3H), 0.84 (s,
3H); 13C NMR (75 MHz, CDCl3): l 149.0, 141.7, 133.4×2,
109.9, 109.0, 54.0, 37.5, 35.1, 33.6, 28.8, 25.5, 24.9, 23.7,
11.8. Anal. calcd for C15H24: C, 88.16; H, 11.84. Found:
C, 87.94; H, 11.87.
Additionally, (+)-g-cyclohomocitral, (S)-3, was con-
verted into (+)-pallescensone, (S)-4, in two steps
according to published procedures.2,10 Reaction with a
solution of 3-furyllithium in THF afforded the
diastereomeric alcohols 8 in 80% yield, and they were
smoothly oxidized with tetrapropylammonium per-
ruthenate (TPAP)11 to give crystalline pallescensone
(mp 54°C) in 70% yield. The crystalline nature of
pallescensone has never been reported.
In conclusion, an asymmetric synthesis of a new mono-
cyclic sesquiterpenoid isolated from P. subobtusa has
been achieved for the first time, and the absolute
configuration has been determined. The merits of this
approach are high-yielding reaction steps and secured
absolute configuration.
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