Propargylamine synthesis by copper-catalyzed oxidative coupling of alkynes and tertiary amine N-oxides

Article abstract of DOI:10.1021/jo201059h

An efficient method for synthesizing N,N-dimethylpropargylamines is described. The synthesis exploited the Cu(II)-catalyzed oxidative alkynylation reaction of trimethylamine N-oxides with alkynes in the absence of external oxidant. Both aromatic and aliph

Full text of DOI:10.1021/jo201059h

NOTE
pubs.acs.org/joc
Propargylamine Synthesis by Copper-Catalyzed Oxidative Coupling of
Alkynes and Tertiary Amine N-Oxides
Zhanwei Xu, Xiaoqiang Yu,* Xiujuan Feng, and Ming Bao*
State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116023, China
S Supporting Information
b
ABSTRACT: An efficient method for synthesizing N,N-di-
methylpropargylamines is described. The synthesis exploited
the Cu(II)-catalyzed oxidative alkynylation reaction of tri-
methylamine N-oxides with alkynes in the absence of external
oxidant. Both aromatic and aliphatic alkynes were utilized to
achieve the corresponding products in moderate to excellent yields. The reaction conditions tolerated ester, hydroxy, and
aldehyde groups.
he development of convenient and efficient methods for the
synthesis of propargylamines has attracted considerable
Scheme 1. Reaction of Terminal Alkynes with Iminium Ion
Intermediates
T
attention. Propargylamines can be utilized as versatile and
key synthetic intermediates for the preparation of several natural
products1 and bioactive compounds.2 Over the past two decades,
three main methods have been developed for the preparation of
propargylamines. One method involves the substitution reac-
tions of functionalized tertiary amines with alkynyllithium, -mag-
nesium,3 or -aluminum4 reagents. These reactions need leaving
groups and stoichiometric nucleophiles. Another method in-
volves the transition-metal-catalyzed three-component one-pot
coupling reactions (A3-coupling reactions) of aldehydes, alkynes,
and secondary amines. These reactions require prefunctionalized
aldehydes to form iminium ion intermediates in situ.5À7 The last
method involves the copper- and iron-catalyzed direct oxidative
alkynylations of CÀH bonds in tertiary amines. These reactions
also proceed via iminium ion intermediates generated from the
oxidative dehydrogenation reactions8 of tertiary amines with an
In our initial studies, the reaction of phenylacetylene (1a) with
trimethylamine N-oxide dihydrate (2) was chosen as a model
reaction for optimizing the reaction conditions. The optimiza-
tion included selecting the most suitable copper catalysts and sol-
vents at 110 °C under a nitrogen atmosphere (Table 1). Several
copper salts were tested in tetrahydrofuran (THF). These include
CuBr, CuI, Cu(II) trifluoromethanesulfonate [Cu(OTf)2], Cu-
(II) acetate monohydrate [Cu(OAc)2 H2O], CuF2 2H2O, and
oxidant such as tBuOOH,9 N-bromosuccinimide,10 or (tBuO)2
11
in situ (Scheme 1). Among these methods, the third one is the
most economical and practical. However, the requirement of ex-
ternal oxidants is disadvantageous because some alkynes bearing
sensitive substituents such as the aldehyde group could not be
used. In addition, aliphatic alkynes usually have low reactivities in
such reactions.
3
3
Cu(II) acetylacetonate [Cu(acac)2] (entries 2À7). The Cu(II)
salts exhibited higher catalytic activities than Cu(I) salts, and
Cu(acac)2 had the highest activity. On the contrary, the Cu(I)
salt CuBr demonstrated the most effective catalytic activity in the
oxidative alkynylations of tertiary amines in the presence of an
oxidant.9 No reaction was observed in the absence of a copper
catalyst (entry 1). The solvents were then screened using Cu-
(acac)2 as the catalyst (entries 8À12). Both polar [THF, dioxane,
and acetonitrile (CH3CN)] and nonpolar solvents [1,2-di-
methoxyethane (DME), 1,2-dichloroethane, (DCE), and methyl
tert-butyl ether (MTBE)] were examined, and DME proved to be
the best solvent (entry 10). Therefore, the subsequent reactions
of the terminal alkynes 1aÀp with trimethylamine N-oxide
Iminium ion intermediates12 could also be generated by the
decomposition of corresponding tertiary amine N-oxides. The
decomposition requires appropriate promoters such as trifluor-
oacetic anhydride,13 sulfur dioxide,14 iron salts,15 and copper salts.16
Moreover, we supposed that tertiary amine N-oxides may also
undergo direct oxidative alkynylations in the presence of a cop-
per salt without using an external oxidant. Indeed, when the reac-
tions of trimethylamine N-oxide with various terminal alkynes
were treated at the optimized conditions, N,N-dimethylpropar-
gylamines were obtained in satisfactory yields (Scheme 1). This
protocol showed a broad substrate scope and good functional
group tolerance, and we report our results herein.
Received: May 30, 2011
Published: July 15, 2011
r
2011 American Chemical Society
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NOTE
Table 1. Catalyst and Solvent Screeninga
Scheme 2. Reactions of N-Methylmorpholine N-Oxide
Monohydrate (4) and Benzyldimethylamine N-Oxide (5)
entry
catalyst
none
solvent
time (h)
yieldb (%)
1
2
THF
12
6
N.R.c
48
CuBr
THF
3
CuI
THF
4
trace
74
4
Cu(OTf)2
THF
12
10
12
10
12
4
5
Cu(OAc)2 H2O
THF
62
3
Scheme 3. Possible Mechanism for the Direct Oxidative
Alkynylation of Tertiary Amine N-Oxides to Propargylamines
6
CuF2 2H2O
THF
62
3
7
Cu(acac)2
Cu(acac)2
Cu(acac)2
Cu(acac)2
Cu(acac)2
Cu(acac)2
THF
77
8
dioxane
CH3CN
DME
DCE
77
9
trace
84
10
11
12
4
6
24
MTBE
10
trace
a Reaction conditions: phenylacetylene (51.1 mg, 0.5 mmol), trimethy-
lamine N-oxide dihydrate (111.1 mg, 1.0 mmol), catalyst (0.05 mmol),
solvent (2.0 mL), 110 °C, under a nitrogen atmosphere. b Isolated yield.
c No reaction.
dihydrate 2 were performed in the presence of Cu(acac)2 as a
catalyst in DME at 110 °C under a nitrogen atmosphere.
The reactions of the terminal alkynes 1aÀp with trimethyla-
mine N-oxide dihydrate 2 were performed under the optimized
conditions, and the results are summarized in Table 2. The
reactions of the aromatic alkynes phenylacetylene (1a) and
4-methylphenylacetylene (1b) with trimethylamine N-oxide
dihydrate 2 smoothly proceeded to furnish the corresponding
popargylamines 3a and 3b in high yields (84% and 93%, res-
pectively; entries 1 and 2). There was a slight decrease in the
reaction yield when 4-bromophenylacetylene (1c), which bore
the electron-withdrawing group Br on its benzene ring, was exa-
mined (80% yield of 3c; entry 3). However, only a moderate yield
was obtained from the reaction of 2 with 4-fluorophenylacetylene
(1d), which bore the strong electron-withdrawing group F on its
benzene ring (68% yield of 3d; entry 4). These results indicated
that the reaction yield was remarkably influenced by the electro-
nic property of the substituent linked on the benzene ring of the
aromatic alkyne. Regarding the aliphatic alkynes 1eÀp (entries
5À17), all except 1f underwent the desired reactions efficiently
to give the corresponding products 3e and 3gÀp in moderate to
good yields (entries 5, 7À16; 67%À89% yields). Previous studies
have shown that aliphatic alkynes showed poor reactivities in the
copper-catalyzed direct oxidative alkynylation of tertiary amines
in the presence of an oxidant.9 In the present study, product
1-(N,N-dimethylamino)-4-phthalimido-2-butyne (3h) appeared
to be an interesting intermediate that can be used for the syn-
thesis of propargylic diamines.17 The reaction conditions em-
ployed were found to tolerate ester, hydroxy, and aldehyde
groups. Aldehyde group is well-known to be easily oxidized to
carboxyl group in the presence of a conventional oxidant.
The above results prompted us to investigate the direct
oxidative alkynylation of other tertiary amine N-oxides to
determine the scope of tertiary amine N-oxide substrates. When
N-methylmorpholine N-oxide monohydrate (4)18 and benzyldi-
methylamine N-oxide (5) were treated with phenylacetylene
under standard conditions, the corresponding products 6 and
7 were obtained in low yields (48% and 35%, respectively;
Scheme 2).
A possible mechanism19 for the direct oxidative alkynylation
of tertiary amine N-oxides to propargylamines is shown in
Scheme 3. The reaction of 2 with a Cu(II) catalyst16 could pro-
duce the iminium ion intermediate 8 (coordinated to copper
hydroxide). This intermediate could then react with phenylace-
tylene to generate iminium ion intermediate 9 (coordinated to
copper acetylide). The nucleophilic attack9b of copper acetylide
on the iminium ion intermediate 9 yields the desired product 3a.
The Cu(II) catalyst is regenerated after the reaction. The reac-
tions of the less acidic aliphatic alkynes also proceeded efficiently
to give the corresponding products in satisfactory yields. The
efficiency is possibly attributed to the strong basicity of the [Cu]-
OH generated in situ.
In conclusion, we have established a new, simple, and effective
method for synthesizing propargylamines using tertiary amine
N-oxides in the absence of external oxidant. Aside from aromatic
alkynes, the less acidic aliphatic alkynes could also be utilized in
the Cu(II)-catalyzed direct oxidative alkynylation of trimethyla-
mine N-oxide. Although the reactions of some tertiary amine
N-oxides showed inferior efficiencies, the present method can be
valuably complemented with previous methods for synthesizing
propargylamines.
’ EXPERIMENTAL SECTION
All reactions were carried out under a nitrogen atmosphere using
standard Schlenk techniques. THF, DME, dioxane, and MTBE were
distilled from sodium/benzophenone. DCE and MeCN were distilled
from CaH2. NMR spectra were run in CDCl3 on a 400 MHz instrument
and recorded at the following frequencies: proton (1H, 400 MHz),
carbon (13C, 100 MHz).
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Table 2. Copper-Catalyzed Oxidative Alkynylation of the CÀH Bond in Trimethylamine N-Oxide To Yield Propargylaminesa
a Conditions: terminal alkyne 1 (0.5 mmol), trimethylamine N-oxide dihydrate (111.1 mg, 1.0 mmol), Cu(acac)2 (13.1 mg, 0.05 mmol), DME (2.0 mL),
110 °C, nitrogen atmosphere. b Isolated yield. c DME (4.0 mL) was used. d Reaction was carried out at 120 °C.
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NOTE
General Procedure for the Synthesis of Propargylamines
(3aÀp). Amixtureofalkyne(0.5mmol), Cu(acac)2 (13.1 mg, 0.05 mmol),
trimethylamine N-oxidedihydrate(111.1mg,1.0mmol),andDME(2.0mL)
was placed in a 25 mL sealed tube under a nitrogen atmosphere. The mixture
was then stirred at 110 °C until the reaction was completed (as determined
by thin-layer chromatography). The solvent was then removed under re-
duced pressure. Finally, the residue was purified by chromatography on silica
gel (petroleum ether:ethyl acetate, 3:1) to afford propargylamines.
N,N-Dimethyl-3-phenylprop-2-yn-1-amine (3a):20 yield 84%, 66.9 mg,
colorless oil; 1H NMR (CDCl3, 400 MHz) δ 2.37 (s, 6H), 3.47 (s, 2H),
7.29À7.30 (m, 3H), 7.43À7.45 (m, 2H); 13C NMR (CDCl3, 100 MHz)
δ 44.3, 48.6, 84.6, 85.2, 123.2, 128.0, 128.3, 131.7.
825, 1013, 1038, 1106, 1209, 1359, 1456, 1508, 2776, 2831, 2860, 2941,
3045 cmÀ1; HRMS (EI) m/z calcd. for C13H17NO2 [M]+ 219.1259,
found 219.1254.
4-(2-Bromo-4-methoxyphenoxy)-N,N-dimethylbut-2-yn-1-amine (3l):
yield 72%, 107.4 mg, yellow oil; 1H NMR (CDCl3, 400 MHz) δ 2.25 (s,
6H), 3.28 (s, 2H), 3.77(s, 3H), 4.75 (s, 2H), 6.81 (dd, J = 10.0 Hz, 3.0 Hz,
1H), 7.04 (d, J = 10.0 Hz, 1H), 7.12 (d, J = 3.0 Hz, 1H); 13C NMR (CDCl3,
100 MHz) δ 44.1, 48.0, 55.8, 58.3, 79.7, 83.2, 113.3, 113.6, 116.3, 118.8,
148.5, 154.8; IR (neat) 800, 842, 863, 1002, 1041, 1105, 1213, 1277, 1456,
1493, 1575, 1604, 2776, 2824, 2860, 2940 cmÀ1; HRMS (EI) m/z calcd for
C13H16NO2Br [M]+ 297.0364, found 297.0367.
Methyl 4-((4-(dimethylamino)but-2-yn-1-yl)oxy)benzoate (3m):
1
N,N-Dimethyl-3-(p-tolyl)prop-2-yn-1-amine (3b):21 yield 93%, 81.0
mg, colorless oil; 1H NMR (CDCl3, 400 MHz) δ 2.34 (s, 3H), 2.37 (s,
6H), 3.46 (s, 2H), 7.11 (d, J = 7.8 Hz, 2H), 7.33 (d, J = 7.9 Hz, 2H); 13C
NMR (CDCl3, 100 MHz) δ 21.6, 44.4, 48.8, 84.0, 85.4, 120.3, 129.2,
131.7, 138.2.
yield 76%, 94.0 mg, light yellow oil; H NMR (CDCl3, 400 MHz) δ
2.26 (s, 6H), 3.29 (s, 2H), 3.89 (s, 3H), 4.79 (s, 2H), 7.01 (d, J = 8.8 Hz,
2H), 8.00 (d, J = 8.8 Hz, 2H); 13C NMR (CDCl3, 100 MHz) δ 44.3,
48.1, 52.1, 56.4, 79.4, 83.5, 114.7, 123.4, 131.7, 161.5, 166.9; IR (neat)
846, 1003, 1105, 1171, 1281, 1435, 1509, 1581, 1606, 1717, 2776, 2823,
2861, 2948 cmÀ1; HRMS (EI) m/z calcd for C14H17NO3 [M]+
247.1208, found 247.1203.
(4-((4-(Dimethylamino)but-2-yn-1-yl)oxy)phenyl)methanol (3n):
yield 72%, 79.0 mg, colorless solid; mp 61À63 °C; 1H NMR (CDCl3,
400 MHz) δ 1.88 (s, 1H), 2.25 (s, 6H), 3.27 (s, 2H), 4.62 (s, 2H), 4.73
(s, 2H), 6.97 (d, J = 8.4 Hz, 2H), 7.30 (d, J = 8.3 Hz, 2H); 13C NMR
(CDCl3, 100 MHz) δ 44.2, 48.0, 56.3, 64.9, 80.1, 82.7, 115.0, 128.6,
134.3, 157.3; IR (neat) 812, 1010, 1175, 1216, 1458, 1511, 1586, 1610,
2782, 2826, 2866, 2945, 3358 cmÀ1; HRMS (EI) m/z calcd. for
C13H17NO2 [M]+ 219.1259, found 219.1254.
4-((4-(Dimethylamino)but-2-yn-1-yl)oxy)benzaldehyde (3o): yield
74%, 80.6 mg, yellow oil; 1H NMR (CDCl3, 400 MHz) δ 2.26 (s, 6H),
3.29 (s, 2H), 4.82 (s,2H), 7.10 (d, J = 8.7 Hz, 2H), 7.85 (d, J = 8.8 Hz,
2H), 9.90 (s, 1H); 13C NMR (CDCl3, 100 MHz) δ 44.2, 48.0, 56.4, 79.1,
83.8, 115.3, 130.5, 131.9, 162.6, 190.9; IR (neat) 832, 1000, 1162, 1225,
1455, 1508, 1579, 1600, 1696, 2777, 2823, 2941 cmÀ1; HRMS (EI) m/z
calcd for C13H15NO2 [M]+ 217.1103, found 217.1111.
3-(4-Bromophenyl)-N,N-dimethylprop-2-yn-1-amine (3c): yield 80%,
95.3 mg, colorless oil; 1H NMR (CDCl3, 400 MHz) δ 2.36 (s, 6H), 3.45
(s, 2H), 7.30 (d, J = 8.3 Hz, 2H), 7.43 (d, J = 8.2 Hz, 2H); 13C NMR
(CDCl3, 100 MHz) δ 44.5, 48.7, 84.3, 86.1, 122.3, 122.4, 131.7, 133.3;
HRMS (EI) m/z calcd for C11H12NBr [M]+ 237.0153, found 237.0158.
3-(4-fluorophenyl)-N,N-dimethylprop-2-yn-1-amine (3d):21 yield
1
68%, 60.4 mg, colorless oil; H NMR (CDCl3, 400 MHz) δ 2.36 (s,
6H), 3.45 (s, 2H), 6.97À7.02 (m, 2H), 7.40À7.43 (m, 2H); 13C NMR
(CDCl3, 100 MHz) δ 44.4, 48.7, 84.3, 84.5, 115.6 (d, J = 11.9 Hz), 119.4,
133.7 (d, J = 8.2 Hz), 162.5 (d, J = 247.4 Hz); HRMS (EI) m/z calcd for
C11H12NF [M]+ 177.0954, found 177.0954.
3-Cyclohexyl-N,N-dimethylprop-2-yn-1-amine (3e):22 yield 85%,
70.3 mg, colorless oil; 1H NMR (CDCl3, 400 MHz) δ 1.26À1.77
(m, 10H), 2.28 (s, 6H), 2.40 (m, 1H), 3.21 (s, 2H); 13C NMR (CDCl3,
100 MHz) δ 25.0, 26.1, 29.2, 33.1, 44.3, 48.4, 74.8, 89.8.
N,N-Dimethylundec-2-yn-1-amine (3f):23 yield 53%, 51.9 mg, color-
less oil; 1H NMR (CDCl3, 400 MHz) δ 0.86À0.90 (m, 3H), 1.27À1.49
(m, 12H), 2.18À2.22 (m, 2H), 2.28 (s, 6H), 3.20 (s, 2H); 13C NMR
(CDCl3, 100 MHz) δ 14.3, 18.9, 22.8, 29.06, 29.09, 29.3, 29.4, 32.0, 44.3,
48.4, 75.0, 85.6.
2-((4-(Dimethylamino)but-2-yn-1-yl)oxy)benzaldehyde (3p): yield
68%, 73.9 mg, yellow oil; 1H NMR (CDCl3, 400 MHz) δ 2.25 (s, 6H),
3.28 (s, 2H), 4.87 (s, 2H), 7.07 (dd, J = 7.6 Hz, 7.4 Hz, 1H), 7.14 (d,
J = 8.4 Hz, 1H), 7.56 (dd, J = 8.4 Hz, 7.4 Hz, 1H), 7.85 (d, J = 7.7 Hz,
1H), 10.49 (s, 1H); 13C NMR (CDCl3, 100 MHz) δ 44.2, 48.0, 56.9,
79.1, 83.9, 113.5, 121.5, 128.5, 135.7, 160.6, 189.6; IR (neat) 758, 999,
N,N-Dimethyl-5-phenylpent-2-yn-1-amine (3g):22 yield 84%, 79.0 mg,
1
colorless oil; H NMR (CDCl3, 400 MHz) δ 2.26 (s, 6H), 2.52 (tt,
J = 7.6 Hz, 2.0 Hz, 2H), 2.84 (t, J = 7.6 Hz, 2H), 3.22 (t, J = 2.0 Hz),
7.19À7.23 (m, 3H), 7.27À7.31 (m, 2H); 13C NMR (CDCl3, 100 MHz) δ
20.9, 35.4, 44.2, 48.2, 75.8, 84.5, 126.3, 128.4, 128.5, 140.8.
1102, 1219, 1459, 1482, 1599, 1689, 2776, 2823, 2861, 2940 cmÀ1
;
HRMS (ES) m/z calcd for C13H16NO2 [M + H]+ 218.1181, found
218.1182.
2-(4-(Dimethylamino)but-2-yn-1-yl)isoindoline-1,3-dione (3h):17
1
Procedure for the Synthesis of Propargylamine 4-(3-
Phenylprop-2-yn-1-yl)morpholine (6).25 A mixture of phenyla-
cetylene (51.1 mg, 0.5 mmol), Cu(acac)2 (13.1 mg, 0.05 mmol),
N-methylmorpholine N-oxide monohydrate (202.8 mg, 1.5 mmol),
and DME (2.0 mL) was placed in 25 mL sealed tube under a nitrogen
atmosphere. The mixture was then stirred at 110 °C until the reaction
was complete (as determined by thin-layer chromatography). The
solvent was then removed under reduced pressure. Finally, the residue
was purified by chromatography on silica gel (petroleum ether/
ethyl acetate, 3:1) to afford 6 (colorless oil) in 48% yield (48.5 mg):
1H NMR (CDCl3, 400 MHz) δ 2.65 (t, J = 4.6 Hz, 4H), 3.51 (s, 2H),
3.77 (t, J = 4.6 Hz, 4H), 7.29À7.32 (m, 3H), 7.42À7.45 (m, 2H); 13C
NMR (CDCl3, 100 MHz) δ 48.2, 52.6, 67.0, 84.2, 85.7, 123.1, 128.3,
128.4, 131.8.
Procedure for the Synthesis of N-Benzyl-N-methyl-3-
phenylprop-2-yn-1-amine (7).9b A mixture of phenylacetylene
(51.1 mg, 0.5 mmol), Cu(acac)2 (0.05 mmol), N,N-dimethyl-1-phenyl-
methanamine oxide (151.2 mg, 1.0 mmol), and DME (2.0 mL) was
placed in 25 mL sealed tube under a nitrogen atmosphere. The mixture
wasthen stirredat 110°Cuntilthereaction was completed(as determined
by thin-layer chromatography). The solvent was then removed under
yield 71%, 86.3 mg, white solid, mp 94À96 °C; H NMR (CDCl3,
400 MHz) δ 2.26 (s, 6H), 3.21 (t, J = 1.8 Hz, 2H), 4.50 (t, J = 1.9 Hz,
2H), 7.73À7.75 (m, 2H), 7.87À7.89 (m, 2H); 13C NMR (CDCl3, 100
MHz) δ 27.3, 44.2, 47.9, 78.42, 78.43, 123.5, 132.1, 134.1, 167.1.
N,N-Dimethyl-4-phenoxybut-2-yn-1-amine (3i):24 yield 89%, 84.3 mg,
colorless oil; 1H NMR (CDCl3, 400 MHz) δ 2.27 (s, 6H), 3.29 (s, 2H),
4.74 (s, 2H), 6.70À7.00 (m, 3H), 7.28À7.32 (m, 2H);13C NMR(CDCl3,
100 MHz) δ 44.1, 48.0, 56.1, 80.0, 82.7, 115.0, 121.3, 129.4, 157.7.
N,N-Dimethyl-4-(4-nitrophenoxy)but-2-yn-1-amine (3j): yield 79%,
92.7 mg, yellow oil; 1H NMR (CDCl3, 400 MHz) δ 2.26 (s, 6H), 3.28 (t,
J = 1.8 Hz, 2H), 4.84 (t, J = 1.8 Hz, 2H), 7.06 (d, J = 9.3 Hz, 2H), 8.22 (d,
J = 9.3 Hz, 2H); 13C NMR (CDCl3, 100 MHz) δ 44.4, 48.1, 56.9, 78.6,
84.4, 115.2, 126.0, 142.1, 162.7; IR (neat) 752, 845, 997, 1111, 1230,
1261, 1342, 1455, 1514, 1591, 1608, 2778, 2823, 2862, 2940, 3084 cmÀ1
;
HRMS (EI) m/z calcd for C12H14N2O3 [M]+ 234.1004, found
234.1001.
4-(4-Methoxyphenoxy)-N,N-dimethylbut-2-yn-1-amine (3k): yield
83%, 91.0 mg, colorless oil; 1H NMR (CDCl3, 400 MHz) δ 2.26 (s, 6H),
3.28 (t, J = 1.8 Hz, 2H), 3.77 (s, 3H), 4.68 (t, J = 1.9 Hz, 2H), 6.84 (d, J =
9.2 Hz, 2H), 6.93 (d, J = 9.2 Hz, 2H); 13C NMR (CDCl3, 100 MHz)
δ 44.1, 48.0, 55.7, 56.9, 80.2, 82.6, 114.5, 116.1, 151.8, 154.3; IR (neat)
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NOTE
reduced pressure. Finally, the residue was purified by chromatography on
silica gel (petroleum ether:ethyl acetate, 10:1) to afford 7 (colorless oil)
in 35% yield (41.5 mg): 1H NMR (CDCl3, 400 MHz) δ 2.40 (s, 3H), 3.51
(s, 2H), 3.64 (s, 2H), 7.24À7.38 (m, 8H), 7.46À7.48 (m, 2H); 13C NMR
(CDCl3, 100 MHz) δ 42.2, 45.9, 60.4, 84.6, 85.9, 123.5, 127.4, 128.2,
128.4, 128.5, 129.4, 131.9, 138.6.
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’ ASSOCIATED CONTENT
S
Supporting Information.
Characterization for com-
b
pounds, including copies of 1Hand13C NMR spectra. This material
is available free of charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
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Corresponding Author
*E-mail: mingbao@dlut.edu.cn, yuxiaoqiang@dlut.edu.cn.
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’ ACKNOWLEDGMENT
(19) Hwang, D.-R.; Uang, B.-J. Org. Lett. 2002, 4, 463.
(20) Bieber, L. W.; da Silva, M. F. Tetrahedron Lett. 2004, 45, 8281.
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(23) Shaibakova, M. G.; Makhmudiyarov, G. A.; Khalilov, L. M.;
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We are grateful to the National Natural Science Foundation of
China (Nos. 20972021 and 21072023) for their financial support.
This work was also supported by the Program for Changjiang
Scholars and Innovative Research Teams in Universities (No.
IRT0711) and the Specialized Research Fund for the Doctoral
Program of Higher Education (No. 20090041110012).
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