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W. Stampfer et al. / Tetrahedron: Asymmetry 14 (2003) 275–280
4. Experimental
4.2.4. rac-(E)-5-Octen-3-ol, rac-14a. Compound 14a
was synthesised from rac-5-octyn-3-ol rac-15a (0.50 g,
4.0 mmol) described for rac-13a. Flash chromatogra-
phy (petroleum ether/EtOAc) afforded (E)-alcohol rac-
The following chemicals were purchased from Aldrich:
2-butanone 1b (36,047), rac-2-pentanol 3a (P801-6),
2-pentanone 3b (P810-6), rac-4-pentyn-2-ol 4a (26,899-
2), rac-4-penten-2-ol 6a (P880-7), rac-(E)-3-penten-2-ol
8a (11,128-7) and rac-1-octen-3-ol 10a (O-528-4). rac-3-
Butyn-2-ol 2a (6239), 1-octen-3-one 10b (6312) and
rac-1-octyn-3-ol 11a (8487) were purchased from Lan-
caster, rac-2-butanol 1a (822263) and 3-octanone 9b
(821860) from Merck and rac-3-pentyn-2-ol 5a (77056)
and rac-3-octanol 9a (74870) from Fluka.
1
14a (0.42 g, 83%) as a slightly yellow liquid. H NMR
(360 MHz, CDCl3): l 5.56 (H, dt, J=15.3, 6.2 Hz),
5.40 (H, dt, J=15.2, 1.5 Hz), 3.48 (H, m), 2.15–2.25 (H,
m), 2.02 (3H, hex, J=6.8 Hz), 1.77 (OH, bs), 1.40–1.52
(2H, m), 0.96 (3H, t, J=7.4 Hz), 0.92 (3H, t, J=7.5
Hz); 13C NMR (90 MHz, CDCl3): l 136.1, 124.9, 72.3,
40.2, 29.4, 25.7, 13.8, 10.0.
4.2.5. rac-4-Octyn-3-ol, rac-15a. Commercial 1-pentyne
(8.0 g, 40.3 mmol) was dissolved in anhydrous THF
(120 mL) and cooled to −85°C under argon. t-BuLi (26
mL, 1.7 M in n-hexane, 1.1 equiv.) was added slowly,
while the temperature was maintained below −70°C.
After 5 min at −80°C the solution was allowed to warm
to −15°C within 1.5 h. Propanal (2.34 g, 40.3 mmol,
freshly distilled, in 10 mL THF) was added slowly at
−80°C while the temperature was maintained below
−65°C. After 10 min at −80°C the solution was allowed
to warm slowly to room temperature. After 18 h the
reaction was quenched by acidification (dil. aq. HCl)
and the two-phase system was extracted with Et2O. The
organic phase was washed once with saturated
NaHCO3 and water, dried (Na2SO4) and evaporated.
Flash chromatography (EtOAc/petroleum ether)
afforded rac-4-octyn-3-ol rac-15a (8.2 g, 84%) as a
4.1. General procedure for the microbial oxidation of
rac-sec-alcohols
Lyophilised cells (40 mg) were rehydrated in phosphate
buffer (50 mM, pH 8.0, 0.50 mL) in 1.5 Eppendorf
tubes at 30°C before alcohol (20 mg, 15 mg for C-4 and
C-5 alcohols) and acetone (125 mL) was added (Vtot=
0.625 mL). The vials were shaken at 30°C at 130 rpm
for the indicated time. The reaction was stopped by
extraction with EtOAc (1 mL). After centrifugation, the
organic phase was separated, dried (Na2SO4) and
analysed by GC. Products were identified by NMR
and/or co-injection with independently obtained refer-
ence samples on GC.
4.2. Synthesis of substrates (rac-alcohols)
1
yellow liquid. H NMR (360 MHz, CDCl3): l 4.29 (H,
m), 2.20 (2H, dt, J=7.05, 1.93 Hz), 1.80 (OH, bs),
1.66–1.72 (2H, m), 1.54 (2H, hex, J=7.2 Hz), 1.01 (3H,
t, J=7.0 Hz), 0.99 (3H, t, J=7.4 Hz); 13C NMR (90
MHz, CDCl3): l 85.3, 81.4, 63.9, 31.2, 22.2, 20.7, 13.4,
9.5.
4.2.1. rac-(Z)-3-Penten-2-ol, rac-7a. To a solution of
rac-3-pentyn-2-ol rac-5a (3.13 g, 37.2 mmol) in abs.
EtOH (15 mL) and quinoline (5 mL), Pd (0.35 g, 5% on
CaCO3) was added and the resulting mixture was vigor-
ously stirred under H2 for 3 days. The Z:E ratio
dropped from 55 (1 d) to 20 (3 d). After completion, the
solids were removed by filtration through a plug of
Hyflo Super Cel and crude (Z)-3-penten-2-ol was
obtained from the filtrate by distillation to give 2.1 g
rac-7a (65%, Z:E=10). The product was identified by
comparison of NMR data with literature values.21
4.2.6. (R)-4-Octyn-3-ol, (R)-15a. [h]2D1 +8.4 (c 0.79,
Et2O, 72% e.e.), lit.24 [h]D21 −33.5 (c 0.40 Et2O) 95.5%
e.e. (S)-enantiomer.
4.3. Synthesis of reference compounds (ketones)
4.3.1. 3-Pentyn-2-one, 5b. A solution of rac-3-pentyn-2-
ol rac-5a (0.52 g, 6.15 mmol) in CH2Cl2 (8 mL) was
titrated with a solution of 8N Jones’ reagent (8 h) at
room temperature using a water bath. After complete
consumption of the alcohol the organic phase was
extracted with water, dried (Na2SO4) and concentrated.
Flash chromatography (n-pentane/CH2Cl2) afforded
pure 3-pentyn-2-one (240 mg, 47%). The product was
identified by comparison of NMR data with literature
values.25
4.2.2. rac-(Z)-4-Octen-3-ol, rac-12a. Compound 12a
was synthesised from rac-4-octyn-3-ol rac-15a (1.40 g,
11 mmol) as described for rac-7a. Flash chromatogra-
phy (petroleum ether/EtOAc) afforded (Z)-4-octen-3-ol
rac-12a [1.23 g (86%), Z:E ꢀ20]. The product was
identified by comparison of NMR data with literature
values.22
4.2.3. rac-(E)-4-Octen-3-ol, rac-13a. rac-4-Octyn-3-ol
rac-15a (0.97 g, 7.8 mmol) was dissolved in dry Et2O
(15 mL) and LiAlH4 (0.45 g, 11.5 mmol, 97%) was
added in small portions. The mixture was refluxed until
completion (24 h), then the reaction was quenched with
2N HCl. The organic phase was extracted with water
and aq. NaHCO3 solution. The organic phase was dried
(Na2SO4) and the solvent evaporated. Flash chro-
matography (petroleum ether/EtOAc) afforded E-alco-
hol rac-13a (0.61 g, 61%) as a colourless liquid. The
product was identified by comparison of NMR data
with literature values.23
4.3.2. 4-Penten-2-one, 6b. A suspension of rac-4-penten-
2-ol rac-6a (0.42 g, 5.4 mmol, in 10 mL CH2Cl2) and
PDC (3.8 g, 10 mmol) was vigorously stirred at room
temperature for 8 days. The solids were centrifuged
(13000 rpm). After addition of Et2O (10 mL) the solu-
tion was extracted with 5% aq. HCl and after neutrali-
sation (extraction with aq. NaHCO3 solution and
water) it was dried (Na2SO4). Flash chromatography
(n-pentane/CH2Cl2) afforded pure 4-penten-2-one 6b
1
(20 mg, 5%). H NMR (360 MHz, CDCl3): l 5.82–6.04