Communications
1
H), 3.64 (s, 3H), 4.09–4.18 ppm
[
a]
Table 3. Recovery of aldehydes by distillation.
13
(
m, 1H); C NMR (75 MHz, CDCl3,
1
1
:1 mixture of regioisomers): d=
4.2 (CH ), 22.7, 23.6, 23.7, 24.93
3
and 24.96, 29.0, 29.08 and 29.11,
2
2
3
9.17 and 29.19, 29.32 and 29.34,
9.4, 29.52 and 29.56, 31.89 and
Entry
1
Thiazolium salt
Distillate composition
Residue composition
1.93 (11 CH ), 33.81 and 33.87
2
(
CH ), 34.11 and 34.14 (CH ), 37.88
2 2
and 37.95 (CH ), 51.5 (CH ), 76.45
2
3
aldehydes 5/6 (63:37), 1.42 g (36%)
a-OH ketones 3/8 (95:5), 2.58 g (64%)
and 76.52 (CH), 174.33 and 174.38
C), 212.59 and 212.64 ppm (C).
(
See the Supporting Information for
full characterization data.
2
aldehydes 5/6 (66:34), 2.31 g (58%)
a-OH ketones 3/8 (76:24), 1.69 g (42%)
Procedure for the thiazolylidene-
catalyzed cleavage of a-hydroxy
ketone (3) under microwave con-
ditions: In a 5 mL microwave tube,
a-hydroxy ketone 3 (1:1 mixture of
[
a] Conditions: distillation setup, pregeneration of catalyst from thiazolium salt (10 mol%), K
dry CH CN (4 mL) for 10 min at RT; removal of K CO and evaporation of CH CN; then, a-hydroxy ketone 3 (1:1
mixture of regioisomers, 4.00 g), 1808C, 4–6 mbar, 3 h.
2 3
CO (10 mol%),
3
2
3
3
regioisomers; 65.7 mg, 0.2 mmol, 1 equiv.), 3,4,5-trimethylthiazol-3-
material and optimizing the structure of the catalyst. Further
investigations will also focus on the development of a continu-
ous distillation process.
ium iodide (4; 10.2 mg, 0.04 mmol, 20 mol%), and K CO (5.5 mg,
2
3
0
.04 mmol, 20 mol%) were combined. The tube was flushed with
argon, and dry CH CN (2 mL) was added. The mixture was stirred
3
under microwave irradiation at the desired temperature for
a period of time. The mixture was cooled to room temperature,
and the solvent was evaporated under reduced pressure. The resi-
due was analyzed by GC with hexadecane as an internal standard.
Experimental Section
Methyl 9,10-epoxystearate (2): Following a modified literature
[6]
procedure, in a 50 mL round-bottom three-necked flask, methyl
oleate (1, Alfa Aesar, 96%; 10 mL, 29.4 mmol, 1 equiv.) was mixed
with formic acid (3.6 mL, 94.1 mmol, 3.2 equiv.). Hydrogen peroxide
Procedure for the thiazolylidene-catalyzed cleavage of a-hy-
droxy ketone (3) with recovery of aldehydes by distillation: In
a 25 mL bottom flask, K CO (1.09 mmol, 150.6 mg, 9 mol%) was
2
3
(
7 mL, 234 mmol, 8 equiv.) was added dropwise with a dropping
added to thiazolium salt 16 (359.4 mg, 1.21 mmol, 10 mol%) in dry
funnel over a 15 min period, and an ice bath was used to control
the temperature. Then, the mixture was stirred magnetically at
room temperature for 8 h. The reaction was followed by GC. The
temperature should not exceed 308C. The organic layer was ex-
tracted with heptane (10 mL), neutralized with a saturated NaHCO3
CH CN (4 mL) under an argon atmosphere. The mixture was stirred
3
magnetically at room temperature for 10 min to give a yellow solu-
tion. Then, under argon, the resulting solution was collected using
a syringe and injected into a distillation flask containing the start-
ing material 3 (4.00 g, 12.18 mmol). The residue was washed with
solution (510 mL), and washed with H O (310 mL) and a saturat-
2
CH CN. The solvent used for the generation of the carbene was
3
ed NaCl solution (25 mL). The organic layer was dried using
Na SO , filtered, and concentrated under reduce pressure to give
evaporated first under reduced pressure (4–6 mbar). Then, the mix-
ture was heated at 1808C and stirred for 3 h. The distillate was col-
lected between 58 and 918C under 4–6 mbar to give nonanal (5)
and methyl 9-oxononanoate (6) as a 66:34 mixture (2.31 g, 58%wt.
yield) as determined by GC analysis. The residue (1.69 g, 42%wt.
yield) was recovered as a 76:24 mixture of starting material 3 and
acyloin 8 as determined by GC analysis. If required, the aldehydes
could be separated further by flash chromatography (cyclohexane/
EtOAc 99.8:0.2 to 95:5).
2
4
1
the title compound 2 (8.80 g, 96%) as a colorless liquid. H NMR
300 MHz, CDCl ): d=0.86 (t, 3H, J=6.5 Hz), 1.10–1.52 (m, 24H),
(
3
1
3
2
.52–1.70 (m, 2H), 2.28 (t, 2H, J=7.4 Hz), 2.80–2.96 (m, 2H),
.64 ppm (s, 3H); C NMR (75 MHz, CDCl ): d=14.2 (CH ), 22.8,
5.0, 26.6, 26.7, 27.90, 27.94, 29.1, 29.29, 29.33, 29.4, 29.6, 29.7, 32.0
1
3
3
3
(
(
13CH ), 34.2 (CH ), 51.5 (CH ), 57.28 (CH), 57.33 (CH), 174.3 ppm
2 2 3
C). See the Supporting Information for full characterization data.
Methyl 9(10)-hydroxy-10(9)-oxostearate (3): Following a literature
[23]
procedure, in a 25 mL round-bottom flask, methyl 9,10-epoxy-
Keywords: aldehydes
· biomass · carbenes · cleavage
stearate (2; 1.00 g, 3.2 mmol, 1 equiv.) was dissolved in DMSO
reactions · organocatalysis
(
4 mL, 56.3 mmol, 17.6 equiv.) under an argon atmosphere. Then,
BF ·Et O (0.012 mL, 0.1 mmol, 0.03 equiv.) was added. The mixture
3
2
was heated at 808C and stirred for 22 h. Water (10 mL) was added,
and the organic layer was extracted with CH Cl (410 mL). The or-
2
2
ganic layers were combined, dried using Na SO , filtered, and con-
2
4
centrated under reduced pressure. The residue was purified by
flash column chromatography (cyclohexane/EtOAc 98:2 to 80:20)
to give the unreacted starting material 2 (0.41 g, 41%, R =0.7, cy-
f
clohexane/EtOAc 90:10) and the title compound 3 (0.45 g, 43%,
R =0.4, cyclohexane/EtOAc 90:10) as a white solid (m.p. 36–408C).
f
1
H NMR (300 MHz, CDCl , 1:1 mixture of regioisomers): d=0.85 (t,
3
3
H, J=6.4 Hz), 1.15–1.38 (m, 17H), 1.38–1.70 (m, 6H), 1.70–1.88
(
m, 1H), 2.28 (t, 2H, J=7.4 Hz), 2.31–2.53 (m, 2H), 3.15–3.40 (m,
ChemSusChem 2015, 8, 2481 – 2486
2485
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