CuCl-catalyzed aerobic oxidation of 2,3-allenols to 1,2-allenic ketones with 1:1 combination of phenanthroline and bipyridine as ligands

Article abstract of DOI:10.3762/bjoc.7.51

A protocol has been developed to prepare 1,2-allenyl ketones using molecular oxygen in air or pure oxygen as the oxidant from 2,3-allenylic alcohols with moderate to good yields under mild conditions. In this reaction CuCl (20 mol %) with 1,10-phenanthrol

Full text of DOI:10.3762/bjoc.7.51

CuCl-catalyzed aerobic oxidation of 2,3-allenols to
1,2-allenic ketones with 1:1 combination of
phenanthroline and bipyridine as ligands
Shuxu Gao1, Yu Liu1 and Shengming Ma*1,2
Full Research Paper
Open Access
Address:
Beilstein J. Org. Chem. 2011, 7, 396–403.
1Shanghai Key Laboratory of Green Chemistry and Chemical
Processes, Department of Chemistry, East China Normal University,
3663 North Zhongshan Road, Shanghai 200062, P. R. China and
2State Key Laboratory of Organometallic Chemistry, Shanghai
Institute of Organic Chemistry, Chinese Academy of Sciences, 345
Lingling Lu, Shanghai 200032, P. R. China. Fax: (+86)-21-6260-9305
doi:10.3762/bjoc.7.51
Received: 25 December 2010
Accepted: 11 March 2011
Published: 07 April 2011
This article is part of the Thematic Series "Allene chemistry".
Guest Editor: K. M. Brummond
Email:
Shengming Ma* - masm@sioc.ac.cn
* Corresponding author
© 2011 Gao et al; licensee Beilstein-Institut.
License and terms: see end of document.
Keywords:
allenic ketone; allenol; Cu(I) catalyst; oxidation
Abstract
A protocol has been developed to prepare 1,2-allenyl ketones using molecular oxygen in air or pure oxygen as the oxidant from 2,3-
allenylic alcohols with moderate to good yields under mild conditions. In this reaction CuCl (20 mol %) with 1,10-phenanthroline
(10 mol %) and bipyridine (10 mol %) was used as the catalyst. It is interesting to observe that the use of the mixed ligands is
important for the higher yields of this transformation: With the monoligand approach developed by Markó et al., the yields are rela-
tively lower.
Introduction
The oxidation of alcohols is one of many fundamental reactions 1,2-Allenic ketones have become very useful in organic syn-
in organic synthesis [1,2]. Usually, stoichiometric oxidants such thesis [16-33]. Current methods for the oxidation of allenic
as MnO2 [3], PCC [4], PDC [4], etc. were employed for this alcohols to ketones include oxidation with MnO2 [30,34,35],
type of transformation. However, the cost and the byproducts Swern oxidation [17,24] or Dess–Martin oxidation
derived from these reagents cause economic and environmental [16,17,24,25,28,31-33]: Catalytic aerobic oxidation has not so
problems [5]. In the past decades, much attention has been paid far been reported. Due to the synthetic potential of 1,2-allenyl
to catalytic oxidation of alcohols using molecular oxygen as the ketones, it is desirable to develop an aerobic oxidation protocol
oxidant with Pd [6-10], Cu [11-13], Ru [14,15] as the catalysts.
for 2,3-allenols. In this paper we wish to report the CuCl-
396

Beilstein J. Org. Chem. 2011, 7, 396–403.
catalyzed aerobic oxidation of 2,3-allenols by applying a mixed
ligand approach using copper as the catalyst [12,13].
Table 2: Screening of solvents for the CuCl-catalyzed oxidation of 1aa.
Results and Discussion
After screening the Pd- [6-10] and Ru-catalyzed [14,15] proto-
cols without success, we began a study of the oxidation of
2-hexyl-1-phenylbuta-2,3-diene-1-ol (1a) with O2 based on the
pioneering study of oxidation of normal simple alcohols by
Markó et al. [12]. Under the original conditions [12], the
expected allenylic ketone 2a was obtained in 59% yield when
CuCl and 1,10-phenanthroline were used (Table 1, entry 1). A
series of bases and solvents were then screened for the oxi-
dation of 1a. The results are summarized in Table 1 and
Table 2. We found that (1) K2CO3 is the most effective base
(Table 1, entry 1) and that organic bases such as NEt3 and DBU
are generally ineffective (Table 1, entries 6 and 7); (2) toluene
is the best solvent (Table 2).
entry
solvent
time (h)
yield of 2a (%)
1
2
3
4
5
toluene
CH3CN
DCE
40
48
47
47
47
59b
NRc
31d
20e
NRf
CHCl3
DMF
aThe reaction was carried out using 0.3 mmol of 1a, 20 mol % of CuCl,
20 mol % of phen, 20 mol % of DBAD, and 1.0 equiv of K2CO3 in 3 mL
of solvent under 1 atm of oxygen. bIsolated yield. c64% of 1a was
recovered as determined by 1H NMR analysis. d1H NMR yield using
CH2Br2 as the internal standard. e78% of 1a was recovered as deter-
mined by 1H NMR analysis. f76% of 1a was recovered as determined
by 1H NMR analysis.
In order to improve the yield further, we examined the effect of
ligands. When 2,2'-bipyridine, which has a weaker coordi-
nating ability, was used [36], the yield of 2a was lower
(Table 3, entry 2). With 4,7-diphenyl-1,10-phenanthroline the yield was slightly improved to 66% (Table 3, entry 3). These
experimental results obviously indicated that the CuCl-
catalyzed oxidation of allenic alcohol was influenced by the
Table 1: Screening of bases for the CuCl-catalyzed oxidation of 1aa.
coordinating ability of nitrogen ligands. Consequently, we
carried out the reaction with a mixture of a stronger coordi-
nating ligand together with a relatively weaker coordinating
ligand. Indeed, it was interesting to observe that when 4,7-
diphenyl-1,10-phenanthroline and 2,2'-bipyridine were mixed in
the ratio of 1:1 [37,38], the isolated yield was improved to 82%
(Table 3, entry 6). The yield with 1,10-phenanthroline and 2,2'-
bipyridine (1:1) was 83% (Table 3, entry 10). However, 4,7-
diphenyl-1,10-phenanthroline is relatively expensive (1 g, $ 94,
Aldrich), so the cheaper 1,10-phenanthroline (5 g, $ 26.4,
entry
base
time (h)
yield of 2a (%)b
Aldrich) was used for further study. The effect of ratio of 1,10-
phenanthroline vs 2,2'-bipyridine on the yield was also studied:
A ratio of 1:1 proved to be the best (Table 3, entries 7–12). This
may be explained by considering that the coordination of 2,2'-
bipyridine is important for the formation of the catalytically
active species and may be easily replaced with that of the
alcohol. We also tried N-methylimidazole (NMI), which was
used in oxidation of primary aliphatic alcohols reported by
Markó et al. [13], however, both the turnover and yield were
low (Table 3, entry 14). Both 2,9-dimethyl-4,7-diphenyl-1,10-
phenanthroline and iPr-Pybox were ineffective in this reaction
(Table 3, entries 4 and 5).
1
2
3
4
5
6
7
K2CO3
Na2CO3
Cs2CO3
KHCO3
KOHi
40
48
35
45
48
45
45
59c,d
22e
27d,f,g
15h
39j
NEt3
NRk
NRl
DBU
aThe reaction was carried out using 0.3 mmol of 1a, 20 mol % of CuCl,
20 mol % of phen, 20 mol % of DBAD, and 2.0 equiv of base in 3 mL
of toluene under 1 atm of oxygen unless otherwise stated. b1H NMR
yield using CH2Br2 as the internal standard. c1.0 equiv K2CO3 was
used. dIsolated yield. e50% of 1a was recovered as determined by
1H NMR analysis. f15 mol % of catalyst was used. g32% of 1a was
recovered by column chromatography. h53% of 1a was recovered as
determined by 1H NMR analysis. i100 mg of 3 Å MS and 20 mol % of
KOH was used. j28% of 1a was recovered as determined by 1H NMR
analysis. k70% of 1a was recovered as determined by 1H NMR
analysis. l72% of 1a was recovered by column chromatography.
Some other Cu(I) catalysts, such as CuBr, CuI, and CuCN
were also investigated, but no higher yield was achieved
(Table 4). Further studies led to the observation that air
(300 psi, 35 °C (oil bath)) could be used instead of pure oxygen
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Beilstein J. Org. Chem. 2011, 7, 396–403.
Table 3: Screening for different nitrogen ligands in the CuCl-catalyzed oxidation of 1aa.
entry
1
ligand 1 (mol %)
ligand 2 (mol %)
time (h)
40
yield of 2a (%)b
—
61
2
3
—
—
46
43c
66
14.5
4
5
6
—
—
45
24
NRd
NRe
82
L-B (10)
45.5
(10)
7
8
L-A (17.5)
L-A (15.0)
L-A (12.5)
L-A (10.0)
L-A (7.5)
L-A (5.0)
L-A (2.5)
L-A (5.0)
L-B (2.5)
L-B (5.0)
L-B (7.5)
L-B (10.0)
L-B (12.5)
L-B (15.0)
L-B (17.5)
NMI (7.0)
40
40
40
42
42
40
40
35
79
65
82
83
78
73
68
17
9
10
11
12
13
14f
aThe reaction was carried out using 0.3 mmol of 1a, 20 mol % of CuCl, 20 mol % of nitrogen ligand, 20 mol % of DBAD, and 1.0 equiv of K2CO3 in
3 mL of toluene under 1 atm of oxygen. b1H NMR yields determined by 300 MHz, 1H NMR analysis using CH2Br2 as the internal standard. c52% of 1a
was recovered as determined by 1H NMR analysis. d87% of 1a was recovered as determined by 1H NMR analysis. e82% of 1a was recovered as
determined by 1H NMR analysis. fThe reaction was carried out using 0.5 mmol of 1a, 5 mol % of CuCl, 5 mol % of t-BuOK, 5 mol % of DBAD and the
indicated ligands in 5 mL of C6H5F at 70 °C under 1 atm of oxygen. 52% of 1a was recovered as determined by 1H NMR analysis.
(1 atm, 15–24 °C) to shorten the reaction time from 40 to 10 mol % of 2,2'-bipyridine and 50 mol % of K2CO3 in toluene
10 hours and the yield was similar (86%) (Table 5, entry 1). with air (300 psi, 35 °C) as the oxidant were defined as the stan-
Thus, 20 mol % of CuCl, 10 mol % of 1,10-phenanthroline, dard conditions.
398

Beilstein J. Org. Chem. 2011, 7, 396–403.
Under the standard conditions a series of 1-aryl-2,3-allenols The reaction may be easily carried out on a 1 g scale: the oxi-
were oxidized to the corresponding 1,2-allenic aryl ketones: A dation of allenol 1k afforded the corresponding allenic ketone
para-nitro group led to a 63% yield of 2e (Table 5, entry 5); 2k in 74% yield in 12 hours with just 10 mol % of CuCl and
heteroaryl groups such as furanyl and thienyl were also toler- 5 mol % each of 1,10-phenanthroline and 2,2'-bipyridine
ated under the reaction conditions, affording the corresponding (Scheme 1).
allenic ketones 2f and 2g in 61% and 73% yields, respectively
(Table 5, entries 6 and 7), whilst the reaction of 1-naphthyl-
substituted 1h afforded 2h in 74% yield (Table 5, entry 8). Tri-
substituted allenic alcohol 1j was also oxidized to the corres-
ponding allenic ketone 2j in 91% yield (Table 5, entry 10).
Table 4: Screening of other Cu(I) sources.
Scheme 1: 1 gram scale reaction of allenol 1k.
When the reaction of 1-alkyl-substituted-2,3-allenols oxidation
was conducted under 1 atm of oxygen at 60 °C, 81% of conver-
sion was observed and the corresponding allenic ketones 2l and
entry
Cu(I)
time (h)
isolated yield of 2a
2m were obtained in 58% and 60% isolated yields (72% and
74% based on the starting material consumed), respectively
(Scheme 2). As a comparison, it should be noted that when 1l
was oxidized with air (300 psi, 60 °C), the allenic ketone 2l was
formed in 43% 1H NMR yield with 73% conversion of 1l
within 10 hours.
1
2
3
CuBr
CuI
40
40
41
68%
49%
45%
CuCN
Table 5: The CuCl-catalyzed oxidation of allenic alcohols using air as the oxidanta.
entry
substrate
R2
time (h)
yield (%)b
R1
R3
1
2
Ph
n-C6H13
n-Pr
H (1a)
H (1b)
10
10
6
86 (2a)
83 (2b)
80 (2c)
78 (2d)
63 (2e)
61 (2f)
73 (2g)
74 (2h)
75 (2i)
91 (2j)
p-EtC6H4
p-BrC6H4
p-ClC6H4
p-O2NC6H4
3-furanyl
3-thienyl
1-naphthyl
Ph
3
n-Pr
H (1c)
4
n-C6H13
n-C6H13
n-C6H13
n-C5H11
Me
H (1d)
6
5
H (1e)
6
6
H (1f)
11
8.5
11
11
11
7
H (1g)
8
H (1h)
9
allyl
H (1i)
10
Ph
Bu
n-C5H11 (1j)
aThe reaction was carried out using 0.3 mmol of 1, 20 mol % of CuCl, 10 mol % of phen, 10 mol % of bpy, 20 mol % of DBAD, and 0.5 equiv of
K2CO3 in 3 mL of toluene, air (300 psi, 35 °C (oil bath)). bIsolated yields.
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Beilstein J. Org. Chem. 2011, 7, 396–403.
0.06 mmol), 2-hexyl-1-phenylbuta-2,3-dien-1-ol (69.6 mg,
0.3 mmol), and 1.5 mL of dry toluene. The reaction vessel was
then transferred to an autoclave, which was charged with air to
a pressure of 300 psi, and stirred at 35 °C (oil bath). After 10 h,
the pressure was carefully released in the hood, the mixture
filtered through a short column of silica gel (100–140 mesh)
and washed with diethyl ether. Evaporation of the solvent and
flash chromatography on silica gel (eluent: petroleum ether/
diethyl ether = 30:1) afforded 2a (59.3 mg, 86%): liquid;
1H NMR (300 MHz , CDCl3) δ 7.76 (d, J = 7.2 Hz, 2H), 7.49 (t,
J = 7.4 Hz, 1H), 7.39 (t, J = 7.2 Hz, 2H), 5.04 (t, J = 2.7 Hz,
2H), 2.46–2.35 (m, 2H), 1.58–1.45 (m, 2H), 1.45–1.20 (m, 6H),
0.89 (t, J = 6.6 Hz, 3H) ppm; 13C NMR (75.4 MHz, CDCl3)
δ 217.0, 194.9, 138.3, 131.9, 129.0, 127.8, 106.9, 79.3, 31.6,
28.9, 27.8, 22.6, 14.0 ppm; MS (m/z) 228 (M+, 7.25), 105 (100);
IR (neat) 2927, 2857, 1933, 1653, 1599, 1450, 1312,
1273 cm−1; HRMS-EI (m/z) calcd for C16H20O+ [M+]:
228.1514; found: 228.1517.
Scheme 2: The oxidation of 1l and 1m under 1 atm of oxygen.
Conclusion
In conclusion, we have developed a method for the aerobic oxi- 2-Propyl-1-(4-ethylphenyl)buta-2,3-dien-1-one (2b)
dation of 2,3-allenols, which uses molecular oxygen in air or The reaction of 1,10-phenanthroline (5.3 mg, 0.03 mmol), 2,2'-
pure oxygen as the oxidant. In this reaction, CuCl with a 1:1 bipyridine (4.6 mg, 0.03 mmol), CuCl (5.9 mg, 0.06 mmol),
ratio of 1,10-phenanthroline and bipyridine was used as the K2CO3 (20.8 mg, 0.15 mmol), dry toluene (1.5 mL), DBAD
catalyst to provide the best results. A series of 1,2-allenic (13.7 mg, 0.06 mmol), and 2-propyl-1-(4-ethylphenyl)buta-2,3-
ketones were obtained in moderate to good yields under mild dien-1-ol (64.7 mg, 0.3 mmol)/dry toluene (1.5 mL) afforded 2b
conditions. Compared to the traditional monoligand approach, (53.0 mg, 83%): liquid; 1H NMR (300 MHz, CDCl3) δ 7.73 (d,
allenols are obviously unique demanding a mixed ligands ap- J = 8.1 Hz, 2H), 7.22 (d, J = 8.1 Hz, 2H), 5.05 (t, J = 2.9 Hz,
proach for better yields probably as a consequence of the coor- 2H), 2.69 (q, J = 7.6 Hz, 2H), 2.44–2.32 (m, 2H), 1.63–1.45 (m,
dinating ability of the allene moiety. Further study in this area is 2H), 1.25 (t, J = 7.5 Hz, 3H), 0.99 (t, J = 7.4 Hz, 3H) ppm;
being pursued in this laboratory.
13C NMR (75.4 MHz, CDCl3) δ 216.5, 194.4, 148.8, 135.8,
129.3, 127.3, 106.5, 79.1, 30.1, 28.8, 21.1, 15.1, 13.7 ppm; MS
(m/z) 214 (M+, 1.75), 133 (100); IR (neat) 2964, 2931, 2872,
1933, 1650, 1607, 1458, 1414, 1273, 1182, 1058 cm−1; HRMS-
EI (m/z) calcd for C15H18O+ [M+]: 214.1358; found: 214.1360.
Experimental
General experimental methods for starting
materials
The starting allenols 1a–e, 1i, 1k, 1l, 1m were prepared via the
reaction of propargyl bromides and corresponding aldehydes in
the presence of SnCl2 and NaI in DMF [39,40]; allenols 1f [41],
1g [42], 1h [43], and 1j [44] were prepared as reported. These
starting allenols were purified by flash chromatography before
use.
2-Propyl-1-(4-bromophenyl)buta-2,3-dien-1-one (2c)
The reaction of 1,10-phenanthroline (5.4 mg, 0.03 mmol), 2,2'-
bipyridine (4.6 mg, 0.03 mmol), CuCl (5.9 mg, 0.06 mmol),
K2CO3 (20.6 mg, 0.15 mmol), dry toluene (1.5 mL), DBAD
(13.8 mg, 0.06 mmol), and 2-propyl-1-(4-bromophenyl)buta-
2,3-dien-1-ol (80.3 mg, 0.3 mmol)/dry toluene (1.5 mL)
afforded 2c (64.1 mg, 80%): liquid; 1H NMR (300 MHz,
CDCl3) δ 7.62 (d, J = 8.7 Hz, 2H), 7.52 (d, J = 8.4 Hz, 2H),
5.07 (t, J = 2.9 Hz, 2H), 2.41–2.30 (m, 2H), 1.60–1.45 (m, 2H),
General experimental procedure for the
aerobic oxidation of allenic alcohols
2-Hexyl-1-phenylbuta-2,3-dien-1-one (2a)
Typical procedure: 1,10-phenanthroline (5.5 mg, 0.03 mmol), 0.97 (t, J = 7.5 Hz, 3H) ppm; 13C NMR (75.4 MHz, CDCl3)
2,2'-bipyridine (4.7 mg, 0.03 mmol), CuCl (5.9 mg, δ 217.0, 193.7, 137.0, 131.1, 130.5, 126.7, 106.7, 79.7, 29.7,
0.06 mmol), K2CO3 (20.6 mg, 0.15 mmol), and 1.5 mL of dry 21.1, 13.7 ppm; MS (m/z) 266 (M+ (81Br), 1.68), 264 (M+
toluene were added successively into an oven dried reaction (79Br), 1.76), 185 (100); IR (neat) 2961, 2929, 2870, 1931,
vessel (sealed with a stopper to isolate the contents from atmos- 1653, 1585, 1458, 1391, 1270, 1071, 1010 cm−1; HRMS-EI
pheric moisture). The resulting mixture was stirred at rt for (m/z) calcd for C13H13O81Br+ [M+]: 266.0129; found:
0.5 h. Then the stopper was removed to add DBAD (13.7 mg, 266.0136.
400

Beilstein J. Org. Chem. 2011, 7, 396–403.
2-Hexyl-1-(4-chlorophenyl)buta-2,3-dien-1-one (2d)
2-Pentyl-1-(3-thienyl)buta-2,3-dien-1-one (2g)
The reaction of 1,10-phenanthroline (5.5 mg, 0.03 mmol), 2,2'- The reaction of 1,10-phenanthroline (5.5 mg, 0.03 mmol), 2,2'-
bipyridine (4.8 mg, 0.03 mmol), CuCl (6.0 mg, 0.06 mmol), bipyridine (4.8 mg, 0.03 mmol), CuCl (5.9 mg, 0.06 mmol),
K2CO3 (20.9 mg, 0.15 mmol), dry toluene (1.5 mL), K2CO3 (20.9 mg, 0.15 mmol), dry toluene (1.5 mL), DBAD
DBAD (13.8 mg, 0.06 mmol), and 2-hexyl-1-(4- (13.7 mg, 0.06 mmol), and 2-pentyl-1-(3-thienyl)buta-2,3-dien-
chlorophenyl)buta-2,3-dien-1-ol (79.6 mg, 0.3 mmol)/dry 1-ol (66.4 mg, 0.3 mmol)/dry toluene (1.5 mL) afforded 2g
toluene (1.5 mL) afforded 2d (62.0 mg, 78%): liquid; 1H NMR (48.3 mg, 73%) (eluent: petroleum ether/diethyl ether = 50:1):
(300 MHz, CDCl3) δ 7.70 (d, J = 8.4 Hz, 2H), 7.35 (d, J = 8.4 liquid; 1H NMR (300 MHz, CDCl3) δ 8.07 (d, J = 1.8 Hz, 1H)
Hz, 2H), 5.06 (t, J = 2.6 Hz, 2H), 2.43–2.32 (m, 2H), 1.55–1.42 7.53 (d, J = 4.8 Hz, 1H), 7.25 (dd, J1 = 4.8 Hz, J2 = 3.3 Hz,
(m, 2H), 1.43–1.18 (m, 6H), 0.88 (t, J = 6.3 Hz, 3H) ppm; 1H), 5.16 (d, J = 2.7 Hz, 2H), 2.41–2.32 (m, 2H), 1.56–1.42 (m,
13C NMR (75.4 MHz, CDCl3) δ 217.0, 193.6, 138.2, 136.6, 2H), 1.42–1.24 (m, 4H), 0.90 (t, J = 6.6 Hz, 3H) ppm;
130.4, 128.1, 106.9, 79.6, 31.6, 28.9, 27.7, 22.5, 14.0 ppm; MS 13C NMR (75.4 MHz, CDCl3) δ 216.0, 187.1, 141.5, 132.2,
(m/z) 264 (M+ (37Cl), 0.76), 262 (M+ (35Cl), 2.08), 139 (100); 128.2, 125.1, 107.6, 79.6, 31.4, 27.9, 27.5, 22.4, 14.0 ppm; MS
IR (neat) 2927, 2857, 1931, 1654, 1590, 1460, 1397, 1274, (m/z) 220 (M+, 3.02), 111 (100); IR (neat) 2956, 2927, 2861,
1091 cm−1; HRMS-EI (m/z) calcd for C16H19O35Cl+ [M+]: 1933, 1641, 1511, 1460, 1411, 1260, 1082 cm−1; HRMS-EI
262.1124; found: 262.1130.
(m/z) calcd for C13H16OS+ [M+]: 220.0922; found: 220.0922.
2-Hexyl-1-(4'-nitrophenyl)buta-2,3-dien-1-one (2e)
2-Methyl-1-(1-naphthyl)buta-2,3-dien-1-one (2h)
The reaction of 1,10-phenanthroline (5.5 mg, 0.03 mmol), 2,2'- The reaction of 1,10-phenanthroline (5.5 mg, 0.03 mmol), 2,2'-
bipyridine (4.7 mg, 0.03 mmol), CuCl (5.9 mg, 0.06 mmol), bipyridine (4.8 mg, 0.03 mmol), CuCl (6.2 mg, 0.06 mmol),
K2CO3 (20.8 mg, 0.15 mmol), dry toluene (1.5 mL), DBAD K2CO3 (21.4 mg, 0.15 mmol), dry toluene (1.5 mL), DBAD
(13.9 mg, 0.06 mmol), and 2-hexyl-1-(4-nitrophenyl)buta-2,3- (13.5 mg, 0.06 mmol), and 2-methyl-1-naphthylbuta-2,3-dien-1-
dien-1-ol (82.7 mg, 0.3 mmol)/dry toluene (1.5 mL) afforded 2e ol (63.6 mg, 0.3 mmol)/dry toluene (1.5 mL) afforded 2h
(51.4 mg, 63%) (eluent: petroleum ether/diethyl ether = 20:1): (47.2 mg, 74%, an unknown substance could not be separated
liquid; 1H NMR (300 MHz, CDCl3) δ 8.24 (d, J = 8.7 Hz, 2H), via column chromatography and the purity of 2h is 95%, which
7.84 (d, J = 8.7 Hz, 2H), 5.12 (t, J = 2.9 Hz, 2H), 2.44–2.33 (m, was determined by 1H NMR with mesitylene as the internal
2H), 1.57–1.44 (m, 2H), 1.44–1.20 (m, 6H), 0.89 (t, J = 6.5 Hz, standard): liquid; 1H NMR (300 MHz, CDCl3) δ 8.11–8.03 (m,
3H) ppm; 13C NMR (75.4 MHz, CDCl3) δ 218.0, 193.4, 149.4, 1H), 7.95–7.81 (m, 2H), 7.61–7.39 (m, 4H), 4.80 (q, J = 2.8 Hz,
143.6, 129.7, 123.1, 107.6, 80.4, 31.5, 28.8, 27.7, 27.3, 22.5, 2H), 2.11 (t, J = 2.7 Hz, 3H) ppm; 13C NMR (75.4 MHz,
14.0 ppm; MS (m/z) 273 (M+, 2.56), 150 (100); IR (neat) 2927, CDCl3) δ 218.6, 197.5, 136.8, 133.5, 130.6, 130.4, 128.2,
2857, 1930, 1660, 1602, 1526, 1461, 1349, 1272, 1104, 126.9, 126.5, 126.1, 125.3, 123.9, 104.8, 78.2, 13.8 ppm; MS
1011 cm−1; HRMS-EI (m/z) calcd for C16H19NO3+ [M+]: (m/z) 208 (M+, 63.16), 155 (100); IR (neat) 3059, 1957, 1930,
273.1365; found: 273.1367.
1650, 1508, 1285, 1251, 1204, 1155, 1080, 1059 cm−1; HRMS-
EI (m/z) calcd for C15H12O [M+]: 208.0888; found: 208.0887.
2-Hexyl-1-(3-furanyl)buta-2,3-dien-1-one (2f)
The reaction of 1,10-phenanthroline (5.4 mg, 0.03 mmol), 2,2'- 2-Allyl-1-phenylbuta-2,3-dien-1-one (2i)
bipyridine (4.8 mg, 0.03 mmol), CuCl (6.2 mg, 0.06 mmol), The reaction of 1,10-phenanthroline (5.4 mg, 0.03 mmol), 2,2'-
K2CO3 (21.3 mg, 0.15 mmol), dry toluene (1.5 mL), DBAD bipyridine (4.6 mg, 0.03 mmol), CuCl (6.1 mg, 0.06 mmol),
(13.6 mg, 0.06 mmol), and 2-hexyl-1-(3-furanyl)buta-2,3-dien- K2CO3 (21.5 mg, 0.15 mmol), dry toluene (1.5 mL), DBAD
1-ol (66.2 mg, 0.3 mmol)/dry toluene (1.5 mL) afforded (13.7 mg, 0.06 mmol), and 2-allyl-1-phenylbuta-2,3-dien-1-ol
2f (40.4 mg, 61%): liquid; 1H NMR (300 MHz, CDCl3) δ 8.10 (55.1 mg, 0.3 mmol)/dry toluene (1.5 mL) afforded 2i (41.1 mg,
(s, 1H), 7.37 (s, 1H), 6.81 (d, J = 1.2 Hz, 1H), 5.21 (t, J = 75%) (eluent: petroleum ether/diethyl ether = 40:1): liquid;
2.9 Hz, 2H), 2.39–2.27 (m, 2 H), 1.52–1.38 (m, 2H), 1.38–1.18 1H NMR (300 MHz, CDCl3) δ 7.78 (d, J = 7.8 Hz, 2H), 7.50 (t,
(m, 6H), 0.87 (t, J = 6.5 Hz, 3H) ppm; 13C NMR (75.4 MHz, J = 7.2 Hz, 1H), 7.39 (t, J = 7.5 Hz, 2H), 5.98–5.82 (m, 1H),
CDCl3) δ 215.8, 186.4, 147.4, 143.0, 126.7, 110.0, 108.1, 5.22–5.04 (m, 4H), 3.20–3.14 (m, 2H) ppm; 13C NMR
80.0, 31.6, 28.9, 27.8, 27.6, 22.6, 14.1 ppm; MS (m/z) 218 (M+, (75.4 MHz, CDCl3) δ 217.2, 194.1, 138.0, 134.9, 132.1, 129.0,
3.49), 95 (100); IR (neat) 2956, 2928, 2857, 1933, 1724, 127.8, 116.4, 105.3, 79.8, 32.5 ppm; MS (m/z) 184 (M+, 2.53),
1645, 1561, 1509, 1458, 1379, 1311, 1163, 1077, 1009 cm−1; 105 (100); IR (neat) 3081, 3062, 2982, 1956, 1931, 1651, 1598,
HRMS-EI (m/z) calcd for C14H18O2+ [M+]: 218.1307; found: 1578, 1447, 1422, 1316, 1272 cm−1; HRMS-EI (m/z) calcd for
218.1305.
C13H12O [M+]: 184.0888; found: 184.0889.
401

Beilstein J. Org. Chem. 2011, 7, 396–403.
2-Butyl-1-phenylnona-2,3-dien-1-one (2j)
38.9, 31.6, 28.8, 27.8, 27.2, 26.2, 22.5, 22.3, 14.0, 13.8 ppm;
The reaction of 1,10-phenanthroline (5.6 mg, 0.03 mmol), 2,2'- MS (m/z) 208 (M+, 1.00), 85 (100); IR (neat) 2958, 2929, 2862,
bipyridine (4.9 mg, 0.03 mmol), CuCl (6.2 mg, 0.06 mmol), 1934, 1679, 1461, 1174 cm−1; HRMS-EI (m/z) calcd for
K2CO3 (21.5 mg, 0.15 mmol), dry toluene (1.5 mL), DBAD C14H24O+ [M+]: 208.1827; found: 208.1828.
(14.1 mg, 0.06 mmol), and 2-butyl-1-phenylnona-2,3-dien-1-ol
(82.2 mg, 0.3 mmol)/dry toluene (1.5 mL) afforded 2j [43] 4-Pentyl-1-phenylhexa-4,5-dien-3-one (2m)
(74.8 mg, 91%): liquid; 1H NMR (300 MHz, CDCl3) 7.71 (d, The reaction of 1,10-phenanthroline (6.9 mg, 0.0375 mmol),
J = 7.8 Hz, 2H), 7.50–7.42 (m, 1H), 7.40–7.32 (m, 2H), 5.36 (t, 2,2'-bipyridine (5.9 mg, 0.0375 mmol), CuCl (6.1 mg,
J = 7.2 Hz, 1H), 2.48–2.30 (m, 2H), 2.16–1.96 (m, 2H), 0.06 mmol), K2CO3 (21.4 mg, 0.15 mmol), dry toluene
1.55–1.11 (m, 10H), 0.93 (t, J = 6.9 Hz, 3H), 0.84 (t, J = (1.5 mL), DBAD (13.9 mg, 0.06 mmol), and 2-pentyl-1-
7.2 Hz, 3H) ppm; 13C NMR (75.4 MHz, CDCl3) δ 213.3, 195.7, (phenylethyl)buta-2,3-dien-1-ol (72.7 mg, 0.3 mmol)/dry
138.9, 131.5, 128.8, 127.6, 107.4, 95.0, 31.1, 30.2, 28.6, 28.4, toluene (1.5 mL) afforded 2m (43.8 mg, 60%) (conv. = 81%,
27.8, 22.31, 22.29, 13.89, 13.86 ppm.
yield = 74% (based on the alcohol consumed)): liquid; 1H NMR
(300 MHz, CDCl3) δ 7.31–7.22 (m, 2H), 7.22–7.13 (m, 3H),
5.13 (s, 2 H), 3.02–2.85 (m, 4H), 2.22–2.10 (m, 2H), 1.45–1.20
2-Propyl-1-phenylbuta-2,3-dien-1-one (2k)
The reaction of 1,10-phenanthroline (49.1 mg, 0.27 mmol), 2,2'- (m, 6H), 0.88 (t, J = 6.5 Hz, 3H) ppm; 13C NMR (75.4 MHz,
bipyridine (42.6 mg, 0.27 mmol), CuCl (54.2 mg, 0.54 mmol), CDCl3) δ 216.3, 200.1, 141.3, 128.3, 126.0, 108.6, 79.7, 40.9,
K2CO3 (373.8 mg, 2.7 mmol), dry toluene (9 mL), DBAD 31.4, 30.9, 27.4, 26.1, 22.4, 14.0 ppm; MS (m/z) 242 (M+,
(124.4 mg, 0.54 mmol), and 2-propyl-1-phenylbuta-2,3-dien-1- 0.87), 105 (100); IR (neat) 2956, 2928, 2861, 1933, 1678, 1496,
ol (1.0141 g, 5.4 mmol)/dry toluene (9 mL) afforded 2k 1456, 1171, 1100 cm−1; Anal. calcd for C17H22O: C, 84.25; H,
(0.7512 g, 74%): liquid; 1H NMR (300 MHz, CDCl3) δ 7.76 (d, 9.15. found: C, 84.16; H, 9.50.
J = 7.5 Hz, 2H), 7.50 (t, J = 7.4 Hz, 1H), 7.39 (t, J = 7.5 Hz,
2H), 5.05 (s, 2H), 2.39 (t, J = 7.2 Hz, 2H), 1.62–1.46 (m, 2H),
Supporting Information
0.99 (t, J = 7.5 Hz, 3H) ppm; 13C NMR (75.4 MHz, CDCl3)
δ 217.1, 194.9, 138.3, 131.9, 129.0, 127.8, 106.7, 79.3, 29.9,
Supporting Information File 1
21.1, 13.7 ppm; MS (m/z) 186 (M+, 6.46), 105 (100); IR (neat)
2961, 2932, 2872, 1933, 1651, 1598, 1578, 1447, 1315,
1271 cm−1; HRMS-EI (m/z) calcd for C13H14O+ [M+]:
186.1045; found: 186.1045.
1H and 13C NMR spectra of products prepared.
[http://www.beilstein-journals.org/bjoc/content/
supplementary/1860-5397-7-51-S1.pdf]
General experimental procedure for the oxi-
dation of allenic alcohols with pure oxygen
3-Hexylocta-1,2-dien-4-one (2l)
Acknowledgements
Financial support from the National Basic Research Program of
China (2009CB825300) is greatly appreciated.
Typical procedure: 1,10-phenanthroline (6.9 mg, 0.0375 mmol),
2,2'-bipyridine (5.8 mg, 0.0375 mmol), CuCl (5.9 mg,
0.06 mmol), and K2CO3 (20.9 mg, 0.15 mmol) were added
sequentially to an oven dried Schlenk tube, which was purged
with air and refilled with oxygen (twice). Then 1.5 mL of dry
toluene was added, the resulting mixture was stirred at rt for
0.5 h which was followed by the sequential addition of DBAD
(14.0 mg, 0.06 mmol), 2-hexyl-1-butylbuta-2,3-dien-1-ol
(63.8 mg, 0.3 mmol) and 1.5 mL of dry toluene. After stirring at
60 °C for 24 h, the reaction mixture was filtered through silica
gel (100–140 mesh) and washed with diethyl ether. Evapor-
ation of the solvent and flash chromatography on silica gel
(eluent: petroleum ether/ether = 50:1) afforded 2l (37.1 mg,
58%) (conv. = 81%, yield = 72% (based on the alcohol
consumed)): liquid; 1H NMR (300 MHz, CDCl3) δ 5.14 (d, J =
2.7 Hz, 2H), 2.62 (t, J = 7.4 Hz, 2H), 2.18–2.09 (m, 2H),
1.60–1.47 (m, 2H), 1.42–1.18 (m, 10H), 0.92–0.78 (m, 6H)
ppm; 13C NMR (75.4 MHz, CDCl3) δ 216.2, 201.3, 108.5, 79.3,
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