N-heterocyclic carbene mediated Reformatsky reaction of aldehydes with a-trimethylsilylcarbonyl compounds

Article abstract of DOI:10.1016/j.tet.2012.11.015

N-Heterocyclic carbenes have been employed as highly efficient organocatalysts to mediate silyl-Reformatsky type reaction. In the presence of only 0.5 mol % nucleophilic carbene 1, various aldehydes coupled with α-trimethylsilylethylacetate very smoothly in DMF at room temperature to provide the corresponding β-hydroxyesters in moderate to high yields. α-Trimethylsilylketone and α-trimethylsilylamide can also undergo the addition reaction to give β-hydroxyketone and b-hydroxyamide in moderate yields.

Full text of DOI:10.1016/j.tet.2012.11.015

Tetrahedron 69 (2013) 607e612
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Tetrahedron
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N-Heterocyclic carbene mediated Reformatsky reaction of aldehydes
with a-trimethylsilylcarbonyl compounds
,
b
a
,
a
a
a,
*
Xiao-Lei Zou a, Guang-Fen Du a , Wan-Fu Sun , Lin He , Xiao-Wei Ma , Cheng-Zhi Gu , Bin Dai
*
*
a Key Laboratory for Green Processing of Chemical Engineering of Xinjiang Bingtuan, School of Chemistry and Chemical Engineering, Shihezi University, Xinjiang 832003, PR China
b Center for Physical and Chemical analysis, Xinjiang University, Urumqi, Xinjiang 830046, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 16 June 2012
Received in revised form 14 October 2012
Accepted 2 November 2012
Available online 9 November 2012
N-Heterocyclic carbenes have been employed as highly efficient organocatalysts to mediate silyl-
Reformatsky type reaction. In the presence of only 0.5 mol % nucleophilic carbene 1, various aldehydes
coupled with
corresponding
lamide can also undergo the addition reaction to give
yields.
a
b
-trimethylsilylethylacetate very smoothly in DMF at room temperature to provide the
-hydroxyesters in moderate to high yields. -Trimethylsilylketone and -trimethylsily-
-hydroxyketone and -hydroxyamide in moderate
a
a
b
b
Keywords:
N-Heterocyclic
carbenes
Ó 2012 Elsevier Ltd. All rights reserved.
Aldehydes
a
-Trimethylsilylethylacetate
Reformatsky reaction
-Hydroxyesters
b
1. Introduction
reaction,7 Cyanation reaction,8 Pudovik reaction,9 Cyanomethyla-
tion reaction,10 and other transformation.11 Herein, we would like
to disclose our preliminary results of NHCs catalyzed silyl-
The reaction of
a-halogenated esters, zinc dust, and carbonyl
compounds, named Reformatsky reaction,1 is one of the most
fundamental organic transformations, which provides a convenient
Reformatsky reaction of
reaction mainly mediated by several fluorides12 or organo-
phosphines,13 giving
-hydroxyesters in moderate to high yields.
a-silylester with aldehydes. This type of
synthesis of
b
-hydroxyesters and their derivatives.2 Over the past
b
half-century, great efforts have been made to develop these
reactions, mainly involving heterogeneous reaction with activated
zinc reagents or other metals,3 homogeneous reaction with dia-
lkylzincs4 as well as catalytic enantioselective Reformatsky
reaction.5 However, some drawbacks, such as using stoichiomeric
amounts of metals, unselective dehydration of the desired prod-
ucts, low yield, and poor stereoselectivity restrain the application of
this classical reaction. Therefore, the development of efficiently
catalytic method for Reformatsky-type reaction is extremely
desirable.
As an important type of organocatalyst, N-heterocyclic carbenes
(NHCs) have been applied widely in the formation of CeC bond via
umpolung strategy.6 Recently, we and other groups have demon-
strated the remarkable ability of NHCs to activate organo-silicon
reagents in some important reaction, such as Mukaiyama aldol
2. Results and discussion
Initially, we have selected the coupling of benzaldehyde with
a
-trimethylsilylethylacetate as a model reaction for the optimi-
zation of various reaction parameters. The results are summa-
rized in Table 1. It was observed that 1,3-bis (2,6-
diisopropylphenyl)imidated-2-ylidene (IPr)14 can initiate the re-
action in DMF, giving
b-hydroxyester 9a in 68% yield (Table 1,
entry 1). Encouraged by this result, several different types of NHC
generated in situ from the corresponding precursor and a base
were screened. It was found that NHC derived from imidazolium
salt 2 and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in situ can
catalyze the reaction efficiently (Table 1, entry 2). Whereas NHC
generated from saturated imidazolinium salt 3 only promote the
reaction with low efficiency (Table 1, entry 6). To our surprise,
NHCs derived from thiazolium salts 4, 5, and triazolium salt 6
cannot initiate the reaction at the same conditions (Table 1, en-
tries 7e9). Other media, such as toluene, THF, dichloromethane,
* Corresponding authors. E-mail addresses: duguangfen@shzu.edu.cn (G.-F. Du),
helin@shzu.edu.cn (L. He), db_tea@shzu.edu.cn (B. Dai).
0040-4020/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2012.11.015

608
X.-L. Zou et al. / Tetrahedron 69 (2013) 607e612
Table 1
Table 2
Evaluation of NHCs and conditions for silyl-Reformatsky reactiona
Survey of aldehydes in NHC-catalyzed silyl-Reformatsky reactiona
OH
1) IPr (0.5 mol%)
OH
CHO
CO2Et
DMF, rt
1) NHC, solvent
+
RCHO
Me3SiCH2CO2Et
+
CO2Et
Me3SiCH2CO2Et
2) HCl, 0.5 h
R
2) HCl, 0.5 h
9a
7
7a
8a
8a
9
Entry
Aldehydes
Time
(h)
Product
Yieldb
(%)
Cl
Ar
Cl
N
N
N
N
N
N
Ar
Ar
Ar
Ar
Ar
OH
1
2
3
CHO
CO2Et
Ar=2,6-(i-Pr)2C6H3
1
2
24
72
Ar=1,3,5-Me3C6H2
Ar=2,6-(i-Pr)2C6H3
I
Cl
N
Cl
OH
N
Ph
CHO
OH
OH
S
N
Me
S
N
Bn
N
6
CO2Et
CO2Et
CO2Et
24
23
76
84
4
5
Me
Me
Entry
NHC
1, (10 mol %)
Solvent
Time (h)
Yieldb (%)
OH
CHO
1
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
24
24
24
24
24
24
24
24
24
24
24
24
24
24
24
24
24
36
68
54
29
41
24
17
NR
NR
NR
38
51
36
17
41
71
72
52
d
2c
3c
4c
5c
6c
7c
8c
9c
10
11
12
13
14
15
16
17
18
2, DBU (10 mol %)
2, KO-tBu(10 mol %)
2, Cs2CO3(10 mol %)
2, DIPEA(10 mol %)
3, DBU (10 mol %)
4, DBU (10 mol %)
5, DBU (10 mol %)
6, DBU (10 mol %)
1, (10 mol %)
1, (10 mol %)
1, (10 mol %)
1, (10 mol %)
1, (10 mol %)
3
4
MeO
F
MeO
OH
CHO
24
83
DMF
F
toluene
DCM
Et2O
OH
OH
CHO
CHO
THF
CO2Et
CO2Et
5
6
24
24
89
82
CH3CN
DMF
1, (5 mol %)
1, (0.5 mol %)
1, (0.1 mol %)
No catalyst
Cl
Cl
DMF
DMF DMF
a
8a (1.5 equiv), 7a (1.0 equiv), solvent: 1.0 mL rt.
Isolated yields.
Using 12 mol % NHC-precursors and 10 mol % base.
b
c
F3C
F3C
OH
CHO
ether, and acetonitrile were also evaluated and the results
indicated that DMF was the best choice with respect to yield
(Table 1, entries 10e14). Lowered catalyst loading to 5 mol %, no
obvious effect to the yield was found (Table 1, entry 15). Further
decreased the NHC to 0.5 mol %, good yield was maintained
(Table 1, entry 16). However, lowering the NHC loading to
0.1 mol %, led a dramatic decrease in the yield (Table 1, entry 17).
Finally, a control experiment confirmed that the reaction did not
occur in the absence of NHC (Table 1, entry 18).
The optimized reaction conditions (0.5 mol % IPr, DMF) were
then applied to a variety of aldehydes to investigate the generality
of the reaction. As indicated in Table 2, aryl aldehydes bearing
both electron-donating and electron-withdrawing groups worked
CO2Et
7c
22
76
O2N
O2N
OH
OH
MeO
CHO
CHO
CHO
MeO
CO2Et
CO2Et
CO2Et
8
23
24
21
90
80
87
Br
Br
9
OH
well to give the corresponding
b-hydroxyesters in high yield
O2N
O2N
10
(Table 2, entries 1e7), while the position of the substituents had
no obvious impact on the yield (Table 2, entries 8e14).
Interestingly,
aromatic aldehyde, such as furfural were also proved to be good
candidates for the coupling, gave -hydroxyesters in high yield
(Table 2, entries 15e17). Gratifyingly, cinnamaldehyde was also
good reactant for the addition, offered 9t in 80% yield (Table 2,
entry 18). It is noteworthy to mention that aliphatic aldehydes,
such as phenylpropionaldehyde and cyclohexanecarboxaldehyde
b-naphthaldehyde, heliotrapine as well as hetero-
OH
CHO
CO2Et
b
11
12
21
24
82
93
Cl
Cl
OH
CHO
CF3
CO2Et
can also react with
the alkyl-substituted
respectively (Table 2, entries 19 and 20).
a
-trimethylsilylethylacetate, but only provided
b
-hydroxyester in 32% and 31% yield,
CF3

X.-L. Zou et al. / Tetrahedron 69 (2013) 607e612
609
Table 2 (continued )
Based on the experimental results and previous studies, we
postulate that this coupling reaction proceeds in the following
manner (Scheme 2), NHC attacks the silicon atom of silylated
reagent to form a possible hexavalent silicon intermediate 1, which
might initiate the addition to aldehyde and afford the final
Entry
Aldehydes
Time
(h)
Product
Yieldb
(%)
OH
CHO
Me
CO2Et
CO2Et
b-hydroxyesters after acidic work up.
13
24
24
83
92
Me
N
N
OH
Ar
Ar
CHO
OMe
14
Me
Me
EWG
Me
DMF
Si
Me3SiCH2EWG
DMF
RCHO
OMe
(I)
OH
OH
CHO
CO2Et
CO2Et
15
16
48
23
90
89
CH2EWG
O
R
N
N
Ar
Ar
CHO
O
O
O
O
SiMe3
N
Ar
Ar
N
OH
OSiMe3
HCl
R
CH2EWG
R
CH2EWG
17
18
24
23
83
80
CO2Et
O
CHO
Scheme 2. Plausible mechanism of NHC-catalyzed silyl-Reformatsky reaction of
O
OH
aldehydes.
OH
CHO
CO2Et
CO2Et
3. Conclusions
In summary, we have successfully devised a simple, highly
efficient, mild, and environmentally friendly organocatalyst pro-
moted protocol for the synthesis of b-hydroxycarbonyl compounds.
Further exploration of chiral organocatalysts-mediated asymmetric
silyl-Reformatsky reaction is now in progress in our laboratory.
OH
CHO
19
48
24
32
31
OH
CHO
4. Experimental section
4.1. General methods
CO2Et
20
a
8a (1.5 equiv), 7 (1.0 equiv), solvent: 1.0 mL rt.
Isolated yields.
Performed the reaction at ꢀ50 ꢁC to rt.
b
c
Unless otherwise indicated, all reactions were conducted under
nitrogen atmosphere in oven-dried glassware with magnetic stir-
ring bar. Column chromatograph was performed with silica gel
(200e300 mesh) and analytical TLC on silica gel 60-F254. 1H NMR
(400 MHz), 13C NMR (100 MHz) spectra were recorded on a Varian
Inova-400 spectrometer in CDCl3, with tetramethylsilane as an
Beside
lylcarbonyl compounds, such as
-trimethylsilylamide 8c were also tested for the addition reaction
a
-trimethylsilylethylacetate, other
a-trimethylsi-
a
-trimethylsilylketone 8b and
a
under similar reaction conditions,
b
-hydroxyketone 9u and
internal standard and reported in parts per million (d). EI mass
b
-hydroxyamide 9v can be obtained in 50% and 45% yield,
spectra were measured on Agilent 7890A/5975C GCeMS and
respectively (Scheme 1).
methanol or acetonitrile was used to dissolve the sample. IR spectra
OH
9u, 50%
OH
O
1) IPr (0.5 mol%)
DMF, rt
CHO
Me3SiCH2COMe
+
(1)
2) HCl, 0.5 h
8b
7a
O
1) IPr (0.5 mol%)
DMF, rt
CHO
N
Me3SiCH2CONMe2
+
(2)
2) HCl, 0.5 h
8c
9v, 45%
7a
Scheme 1. Silyl-Reformatsky reaction of a-trimethylsilylketone and a-trimethylsilylamide.

610
X.-L. Zou et al. / Tetrahedron 69 (2013) 607e612
were recorded on KBr films with a Nicolet Avatar 360. All starting
materials were obtained from commercial supplies and used as
received. Anhydrous THF, ether, toluene were distilled from
sodium. Anhydrous DMF was distilled from calcium hydride.
Petroleum ether (PE), where used, has a boiling range of 60e90 ꢁC.
chromatography on silica gel (PE/EtOAc, 8:1) to afford 9e as a col-
orless oil, 61 mg (89%); IR (KBr film): 3465, 2982, 2935, 2903, 1731,
1715, 1593, 1489, 1401, 1370, 1192, 1093, 1010, 828, 543 cmꢀ1 1H
;
NMR (400 MHz, CDCl3)
3.59 (br s, 1H), 4.14 (q, J¼7.2 Hz, 2H), 5.05e5.08 (m, 1H), 7.26e7.31
(m, 4H); 13C NMR (100 MHz, CDCl3)
14.1, 43.3, 61.0, 69.6, 127.1,
128.6, 133.4, 141.1, 172.2; GCeMS (EI): m/z 228.1 (Mþ).
d
1.24 (t, J¼7.2 Hz, 3H), 2.61e2.72 (m, 2H),
d
4.2. General procedure for the preparation of b-hydroxyesters
9aef, 9het
4.2.6. Ethyl 3-hydroxy-3-(4-(trifluoromethyl)phenyl)propanoate (9f)15
Prepared according to general procedure and purified by chroma-
tography on silica gel (PE/EtOAc, 6:1) to afford 9f as a slightly yellow
oil, 64 mg (82%); IR (KBr film): 3470, 3076, 2980, 2930, 2855, 1736,
1670, 1592, 1581, 1511, 1473, 1455, 1333, 1281, 1166, 1092, 1029, 937,
.
IPr (0.6 mg, 0.0015 mmol) was dissolved in 1.0 mL dry DMF and
cooled to 0 ꢁC, then aldehyde (0.3 mmol) and
-trimethylsilyle-
thylacetate (82.4 L, 0.45 mmol) were loaded via syringe under N2.
a
m
Subsequently the reaction solution was stirred at room tempera-
ture until full consumption of the starting aldehyde indicated by
TLC, 3 mL 1 N HCl was added at this moment and the mixture was
continuously stirred for 0.5 h, then the mixture was extracted by
ethyl acetate (3ꢂ15 mL). The combined organic phase was washed
with saturated sodium bicarbonate and H2O, dried by anhydrous
Na2SO4, and concentrated under vacuum. The crude product was
purified through flash column chromatography (silica gel, PE/
EtOAc, 8:1e4:1) to give the desired products.
807, 696 cmꢀ1
;
1H NMR (400 MHz, CDCl3)
d
1.27 (t, J¼7.2 Hz, 3H),
2.71e2.73 (m, 2H), 3.56 (br s, 1H), 4.19 (q, J¼7.2 Hz, 2H), 7.49e7.67 (m,
4H); 13C NMR (100 MHz, CDCl3)
14.1, 43.1, 61.1, 69.6, 122.7, 125.5 (q,
d
J¼4 Hz), 126.0, 130.4 (q, J¼33 Hz), 146.4 (d, J¼1 Hz), 172.2; GCeMS
(EI): m/z 262.1 (Mþ).
4.2.7. Ethyl 3-hydroxy-3-(4-nitrophenyl)propanoate (9g).16 IPr (0.6
mg, 0.0015 mmol) and 4-nitrobenzaldehyde (45 mg, 0.3 mmol) were
dissolved in 1.0 mL dry DMF and cooled to ꢀ50 ꢁC, then
a-trime-
4.2.1. Ethyl 3-hydroxyl-3-phenylpropanoate (9a).5b Prepared accord-
ing to general procedure and purified by chromatography on silica
gel (PE/EtOAc, 6:1) to afford 9a as a colorless oil, 42 mg (72%); IR (KBr
film): 3492, 3089, 3066, 3050, 2985, 2930, 2855, 1734, 1714, 1556,
thylsilylethylacetate (82.4 mL, 0.45 mmol) was loaded via syringe
under N2. Subsequently the reaction solution was stirred from
ꢀ50 ꢁC to room temperature until full consume of the
4-nitrobenzaldehyde indicated by TLC, 3 mL 1 N HCl was added at
this moment and the mixture was continue stirred for 0.5 h, then the
mixture was extracted by ethyl acetate (3ꢂ15 mL). The combined
organic phase was washed with saturated sodium bicarbonate and
H2O. Organic phase was dried by anhydrous Na2SO4 and concen-
trated under vacuum. The crude product was purified through flash
column chromatography (silica gel, PE/EtOAc, 6:1) to afford 9g as
a slightly yellow oil 54 mg (76%); IR (KBr film): 3477, 3090, 2984,
2930, 2902, 1732, 1721, 1648,1581,1535,1478,1446, 1396,1346,1297,
1265, 1194, 1087, 1069, 1034, 906, 813, 736, 689, 617 cmꢀ1; 1H NMR
1457, 1399, 1373, 1314, 1264, 1159, 1116, 1033, 868, 759, 696 cmꢀ1
;
1H NMR (400 MHz, CDCl3)
3.32 (br s,1H), 4.18 (q, J¼7.2 Hz, 2H), 5.12e5.15 (m,1H), 7.26e7.40 (m,
d
1.26 (t, J¼7.2 Hz, 3H), 2.68e2.79 (m, 2H),
4H); 13C NMR (100 MHz, CDCl3)
d 14.2, 43.3, 60.9, 70.3, 125.7, 127.8,
128.5, 142.5, 172.4; GCeMS (EI): m/z 194.0 (Mþ).
4.2.2. Ethyl 3-hydroxyl-3-p-tolylpropanoate (9b).5b Prepared accord-
ing to general procedure and purified by chromatography on silica
gel (PE/EtOAc, 6:1) to afford 9b as a colorless oil, 47 mg (76%); IR (KBr
film): 3487, 2982, 2915, 2863, 1729, 1515, 1452, 1407, 1372, 1294,
(400 MHz, CDCl3)
J¼3.4 Hz,1H), 4.19 (q, J¼7.2 Hz, 2H), 5.22e5.26 (m,1H), 7.52e7.74 (m,
2H), 8.12e8.27 (m, 2H); 13C NMR (100 MHz, CDCl3)
14.1, 43.0, 61.2,
d
1.27 (t, J¼7.2 Hz, 3H), 2.71e2.81 (m, 2H), 3.80 (d,
1189, 1160, 1037, 816 cmꢀ1 1H NMR (400 MHz, CDCl3)
; d 1.26
(t, J¼7.2 Hz, 3H), 2.35(s, 3H), 2.65e2.78 (m, 2H), 3.35 (br s, 1H), 4.17
d
(q, J¼7.2 Hz, 2H), 5.08e5.11 (m, 1H), 7.15e7.27 (m, 4H); 13C NMR
69.2, 121.7 (d, J¼189 Hz), 130.7 (d, J¼233 Hz), 144.7, 148.3, 172.0;
(100 MHz, CDCl3)
d 14.2, 21.1, 43.4, 60.8, 70.2, 125.6, 129.2, 137.4,
GCeMS (EI): m/z 238.1 (Mþ).
139.7, 172.4; GCeMS (EI): m/z 208.1 (Mþ).
4.2.8. Ethyl 3-hydroxy-3-(3-methoxyphenyl)propanoate (9h).17 Pre-
pared according to general procedure and purified by chromatog-
raphy on silica gel (PE/EtOAc, 4:1) to afford 9h as a colorless oil,
60 mg (90%); IR (KBr film): 3489, 2982, 2934, 2901, 2835, 1734,
1710, 1599, 1584, 1556, 1484, 1453, 1378, 1259, 1160, 1041, 855, 787,
4.2.3. Ethyl 3-hydroxy-3-(4-methoxyphenyl)propanoate (9c).5b Pre-
pared according to general procedure and purified by chromatog-
raphy on silica gel (PE/EtOAc, 6:1) to afford 9c as a colorless oil,
56 mg (84%); IR (KBr film): 3494, 2982, 2960, 2936, 2904, 2834,
1729, 1711, 1652, 1505, 1462, 1396, 1371, 1308, 1245, 1168, 1024,
696 cmꢀ1
;
1H NMR (400 MHz, CDCl3)
d
1.26 (t, J¼7.2 Hz, 3H),
832 cmꢀ1
;
1H NMR (400 MHz, CDCl3)
d
1.25 (t, J¼7.1 Hz, 3H),
2.66e2.77 (m, 2H), 3.36 (br s,1H), 3.80 (s, 3H), 4.17 (q, J¼7.2 Hz, 2H),
2.63e2.78 (m, 2H), 3.29 (br s,1H), 3.79 (s, 3H), 4.16 (q, J¼7.1 Hz, 2H),
5.08e5.11 (m, 1H), 6.80e6.95 (m, 2H), 7.23e7.27 (m, 2H); 13C NMR
5.05e5.09 (m, 1H), 6.85e6.89 (m, 2H), 7.26e7.30 (m, 2H); 13C NMR
(100 MHz, CDCl3)
d 14.1, 43.4, 55.2, 60.9, 70.2, 111.1, 113.3, 117.9,
(100 MHz, CDCl3)
d
14.2, 43.4, 55.3, 60.8, 69.9, 113.9, 127.0, 134.8,
129.5, 144.3, 159.8, 172.3; GCeMS (EI): m/z 224.1 (Mþ).
159.1, 172.4; GCeMS (EI): m/z 224.1 (Mþ).
4.2.9. Ethyl 3-(3-bromophenyl)-3-hydroxypropanoate (9i).17 Pre-
pared according to general procedure and purified by chromatog-
raphy on silica gel (PE/EtOAc, 4:1) to afford 9i as a colorless oil,
65 mg (80%); IR (KBr film): 3473, 3064, 2982, 2935, 2903, 2867,
1731, 1711, 1592, 1568, 1473, 1395, 1374, 1290, 1192, 1069, 1038, 891,
4.2.4. Ethyl 3-(4-fluorophenyl)-3-hydroxypropanoate (9d).5b Pre-
pared according to general procedure and purified by chromatog-
raphy on silica gel (PE/EtOAc, 8:1) to afford 9d as a colorless oil,
53 mg (83%); IR (KBr film): 3477, 2980, 2937, 2898, 1730, 1719, 1606,
1560, 1510, 1371, 1300, 1222, 1155, 1037, 839, 662 cmꢀ1
;
1H NMR
1.26 (t, J¼7.2 Hz, 3H), 2.64e2.76 (m, 2H), 3.41
(br s, 1H), 4.18 (q, J¼7.2 Hz, 2H), 5.09e5.12 (m, 2H), 7.00e7.06 (m,
2H), 7.26e7.37 (m, 2H); 13C NMR (100 MHz, CDCl3)
14.1, 43.3, 61.0,
784, 697, 661 cmꢀ1
;
1H NMR (400 MHz, CDCl3)
d
1.26 (t, J¼7.2 Hz,
(400 MHz, CDCl3)
d
3H), 2.66e2.75 (m, 2H), 3.49 (br s, 1H), 4.18 (q, J¼7.2 Hz, 2H),
5.07e5.10 (m, 1H), 7.19e7.55 (m, 4H); 13C NMR (100 MHz, CDCl3)
d
d 14.1, 43.2, 61.0, 69.6, 122.6, 124.3, 128.9, 130.1, 130.8, 144.8, 172.2;
70.0, 115.3 (d, J¼21 Hz), 127.3 (d, J¼8 Hz), 138.3 (d, J¼4 Hz), 161.0,
GCeMS (EI): m/z 272.0 (Mþ).
163.5, 172.3; GCeMS (EI): m/z 212.1 (Mþ).
4.2.10. Ethyl 3-hydroxy-3-(3-nitrophenyl)propanoate (9j).16 Prepared
according to general procedure and purified by chromatography on
silica gel (PE/EtOAc, 4:1) to afford 9j as a slightly yellow oil, 62 mg
4.2.5. Ethyl 3-(4-chlorophenyl)-3-hydroxypropanoate (9e).5b Pre-
pared according to general procedure and purified by

X.-L. Zou et al. / Tetrahedron 69 (2013) 607e612
611
(87%); IR (KBr film): 3493, 3110, 3081, 2982, 2926, 2872, 2860, 2447,
chromatography on silica gel (PE/EtOAc, 8:1) to afford 9p as a col-
orless oil, 63 mg (89%); IR (KBr film): 3465, 3069, 2982, 2903, 2776,
2031, 1846, 1731, 1604, 1501, 1489, 1445, 1368, 1248, 1096, 1038, 930,
2356, 2332, 1732, 1714, 1650, 1607, 1556, 1520, 1395, 1370,1350, 1191,
1069, 1033, 847, 740, 692 cmꢀ1 1H NMR (400 MHz, CDCl3)
; d 1.25
(td, J¼7.2, 0.52 Hz, 3H), 2.66e2.78 (m, 2H), 3.77 (br s, 1H), 4.17
863, 809, 725, 650 cmꢀ1 1H NMR (400 MHz, CDCl3)
; d 1.26
(q, J¼7.2 Hz, 2H), 5.20e5.23 (m, 1H), 7.50e7.72 (m, 2H), 8.10e8.25
(t, J¼7.2 Hz, 3H), 2.60e2.74 (m, 2H), 3.36 (br s, 1H), 4.16 (q, J¼7.2 Hz,
(m, 2H); 13C NMR (100 MHz, CDCl3)
d 14.1, 43.0, 61.2, 69.4, 121.7
2H), 5.01e5.04 (m, 1H), 5.93 (s, 2H), 6.74e6.87 (m, 3H); 13C NMR
(d, J¼189 Hz), 123.7, 126.5, 130.7 (d, J¼233 Hz), 146.0 (d, J¼271 Hz),
(100 MHz, CDCl3) d 14.1, 43.4, 60.8, 70.2, 101.0, 106.3, 108.1, 119.1,
149.8, 172.0; GCeMS (EI): m/z 239.0 (Mþ).
136.7, 147.0, 147.8, 172.3; GCeMS (EI): m/z 238.1 (Mþ).
4.2.11. Ethyl 3-(2-chlorophenyl)-3-hydroxypropanoate (9k).17 Pre-
pared according to general procedure and purified by chromatog-
raphy on silica gel (PE/EtOAc, 6:1) to afford 9k as a colorless oil,
56 mg (82%); IR (KBr film): 3481, 3061, 2982, 2930, 2907, 2866,
2365, 2326, 1722, 1646, 1568, 1535, 1505, 1476, 1436, 1390, 1371,
4.2.17. Ethyl 3-(furan-2-yl)-3-hydroxypropanoate (9q).5f Prepared
according to general procedure and purified by chromatography on
silica gel (PE/EtOAc, 8:1) to afford 9q as a yellow oil, 46 mg (83%); IR
(KBr film): 3457, 3124, 2982, 2934, 1734, 1650, 1631, 1556, 1540,
1504, 1456, 1373, 1314, 1163, 1029, 883, 811, 740, 597 cmꢀ1; 1H NMR
1299, 1262, 1194, 1164, 1125, 1079, 1029, 891, 859, 757 cmꢀ1
NMR (400 MHz, CDCl3)
3.65 (br s, 1H), 4.19 (q, J¼7.2 Hz, 2H), 5.47e5.50 (m, 1H), 7.19e7.64
;
1H
(400 MHz, CDCl3)
d
1.26 (t, J¼7.2 Hz, 3H), 2.79e2.92 (m, 2H), 3.32
d
1.27 (t, J¼7.2 Hz, 3H), 2.54e2.87 (m, 2H),
(br s, 1H), 4.18 (q, J¼7.2 Hz, 2H), 5.11e5.14 (m, 1H), 6.26e6.33 (m,
2H), 7.36e7.37 (m, 2H); 13C NMR (100 MHz, CDCl3)
d 14.1, 39.8, 60.9,
(m, 4H); 13C NMR (100 MHz, CDCl3)
d
14.1, 41.4, 61.0, 67.0, 127.0,
64.2, 106.3, 110.2, 142.2, 154.8, 171.9; GCeMS (EI): m/z 184.0 (Mþ).
127.2, 128.7, 129.3, 131.3, 139.9, 172.5; GCeMS (EI): m/z 228.0 (Mþ).
4.2.18. (E)-Ethyl 3-hydroxy-5-phenylpent-4-enoate (9r).5f Prepared
according to general procedure and purified by chromatography on
silica gel (PE/EtOAc, 6:1) to afford 9r as a colorless oil, 53 mg (80%);
IR (KBr film): 3456, 3083, 3063, 3030, 2982, 2931, 1726, 1649, 1600,
4.2.12. Ethyl 3-hydroxy-3-(2-(trifluoromethyl)phenyl)propanoate (9l)18.
Prepared according to general procedure and purified by chroma-
tography on silica gel (PE/EtOAc, 4:1) to afford 9l as a slightly yellow
oil, 73 mg (93%); IR (KBr film): 3493, 3075, 2986, 2934, 2907, 1734,
1714, 1607, 1540, 1457, 1374, 1314, 1259, 1160, 1116, 1057, 1029, 965,
1498, 1449, 1400, 1369, 1281, 1168, 1098, 968, 852, 774 cmꢀ1 1H
;
NMR (400 MHz, CDCl3)
d
1.27 (t, J¼7.2 Hz, 3H), 2.58e2.68 (m, 2H),
866, 768, 653 cmꢀ1; 1H NMR (400 MHz, CDCl3)
d
1.27 (t, J¼7.2 Hz, 3H),
3.21 (br s, 1H), 4.18 (q, J¼7.2 Hz, 2H), 4.70e4.75 (m, 1H), 6.22 (dd,
J¼6.1, 16.0 Hz, 1H), 6.65 (dd, J¼16.0 Hz, 1H), 7.22e7.25 (m, 1H),
7.29e7.32 (m, 2H), 7.36e7.38 (m, 2H); 13C NMR (100 MHz, CDCl3)
2.60e2.71 (m, 2H), 3.66 (d, J¼2.4 Hz, 1H), 4.20 (q, J¼7.2 Hz, 2H),
5.53e5.56 (m, 1H), 7.36e7.83 (m, 4H); 13C NMR (100 MHz, CDCl3)
d
14.1, 43.4, 61.0, 65.9, 122.9, 125.5, 125.6, 126.5, 127.7, 132.4, 141.4,
d 14.2, 41.6, 60.9, 68.9, 126.5, 127.8, 128.6, 130.0, 130.7, 136.4, 172.2;
172.2; GCeMS (EI): m/z 262.1 (Mþ).
GCeMS (EI): m/z 220.1 (Mþ).
4.2.13. Ethyl 3-hydroxy-3-o-tolylpropanoate (9m).17 Prepared accord-
ing to general procedure and purified by chromatography on silica gel
(PE/EtOAc, 6:1) to afford 9m as a colorless oil, 52 mg (83%); IR (KBr
film): 3481, 3070, 3017, 2982, 2927, 2867,1735,1715,1560,1485,1465,
4.2.19. Ethyl 3-hydroxy-5-phenylpentanoate (9s).5b Prepared accord-
ing to general procedure and purified by chromatography on silica
gel (PE/EtOAc, 8:1) to afford 9s as a colorless oil, 21 mg (32%); IR (KBr
film): 3481, 3057, 3025, 2982, 2926, 2866, 1735, 1714, 1599, 1556,
1496,1457, 1370,1298,1188, 1152, 1025, 938, 752, 696 cmꢀ1; 1H NMR
1372, 1302, 1267, 1186, 1162, 1038, 947, 866, 760, 726, 616 cmꢀ1
;
1H
1.27 (t, J¼7.2 Hz, 3H), 2.34 (s, 3H), 2.60e2.72
(m, 2H), 3.21 (br s, 1H), 4.19 (q, J¼7.2 Hz, 2H), 5.32e5.35 (m, 1H),
7.12e7.50 (m, 4H); 13C NMR (100 MHz, CDCl3)
14.2, 19.0, 42.1, 60.9,
NMR (400 MHz, CDCl3)
d
(400 MHz, CDCl3)
d
1.27(t, J¼7.2 Hz, 3H), 1.69e1.89 (m, 2H),
2.41e2.54 (m, 2H), 2.66e2.86 (m, 2H), 3.09 (br s, 1H), 3.99e4.05 (m,
1H), 4.17 (q, J¼7.2 Hz, 2H), 7.16e7.30 (m, 5H); 13C NMR (100 MHz,
d
67.0, 125.2, 126.4, 127.6, 130.4, 134.3, 140.5, 172.6; GCeMS (EI): m/z
CDCl3) d 14.2, 31.8, 38.1, 41.3, 60.7, 67.2, 125.9, 128.4, 128.5, 141.7,
208.1 (Mþ).
173.0; GCeMS (EI): m/z 222.1 (Mþ).
4.2.14. Ethyl 3-hydroxy-3-(2-methoxyphenyl)propanoate (9n).17 Pre-
pared according to general procedure and purified by chromatog-
raphy on silica gel (PE/EtOAc, 6:1) to afford 9n as a colorless oil,
62 mg (92%); IR (KBr film): 3480, 3070, 2975, 2937, 2836, 1734, 1714,
1603, 1589, 1487, 1459, 1396, 1371, 1286, 1241, 1182, 1150, 1112, 1024,
4.2.20. Ethyl 3-cyclohexyl-3-hydroxypropanoate (9t).5b Prepared
according to general procedure and purified by chromatography on
silica gel (PE/EtOAc, 8:1) to afford 9t as a colorless oil, 19 mg (31%);
IR (KBr film): 3489, 2984, 2922, 2847, 1736, 1700, 1449, 1370, 1310,
1281, 1168, 1100, 1025, 886, 732 cmꢀ1 1H NMR (400 MHz, CDCl3)
;
758, 612 cmꢀ1
;
1H NMR (400 MHz, CDCl3)
d
1.24 (t, J¼7.2 Hz, 3H),
d
0.94e1.21 (m, 5H), 1.26 (t, J¼7.2 Hz, 3H), 1.32e1.38 (m, 1H),
2.64e2.83 (m, 2H), 3.52 (d, J¼5.2 Hz, 1H), 3.82 (s, 3H), 4.15 (q,
1.63e1.66 (m, 2H), 1.72e1.75 (m, 2H), 1.82e1.87 (m, 1H), 2.36e2.52
(m, 2H), 2.87 (br s, 1H), 3.74e3.77 (m, 1H), 4.15 (q, J¼7.2 Hz, 2H); 13C
J¼7.2 Hz, 2H), 5.32e5.36 (m, 1H), 6.84e7.43 (m, 4H); 13C NMR
(100 MHz, CDCl3)
d
14.2, 41.7, 55.2, 60.7, 66.5, 110.3, 120.8, 126.5,
NMR (100 MHz, CDCl3) d 14.2, 26.0, 26.2, 26.4, 28.3, 28.8, 38.6, 43.0,
128.5, 130.6, 156.0, 172.6; GCeMS (EI): m/z 224.1 (Mþ).
60.7, 72.1, 173.6; GCeMS (EI): m/z 200.1 (Mþ).
4.2.15. Ethyl 3-hydroxy-3-(naphthalen-2-yl)propanoate (9o).5b Pre-
pared according to general procedure and purified by chromatogra-
phy on silica gel (PE/EtOAc, 6:1) to afford 9q as a slightly yellow oil,
66 mg (90%); IR (KBr film): 3473, 3053, 2982, 2926, 2860, 1734, 1714,
1603, 1556, 1504, 1457, 1374, 1267, 1176, 1066, 1033, 950, 898, 855,
4.2.21. 4-Hydroxy-4-phenylbutan-2-one (9u).19 IPr (0.6 mg,
0.0015 mmol) was dissolved in 1.0 mL dry DMF and cooled to 0 ꢁC,
then benzaldehyde (30.6
mL, 0.3 mmol) and 1-(trimethylsilyl)
propan-2-one 8b (59 mg, 0.45 mmol) were loaded via syringe
under N2. Subsequently the reaction solution was stirred at room
temperature until full consume of the benzaldehyde indicated by
TLC, 3 mL 1 N HCl was added at this moment and the mixture was
continue stirred for 0.5 h, then the mixture was extracted by ethyl
acetate (3ꢂ15 mL). The combined organic phase was washed with
saturated sodium bicarbonate and H2O. Organic phase was dried by
anhydrous Na2SO4 and concentrated under vacuum. The crude
product was purified through flash column chromatography (silica
gel, PE/EtOAc, 4:1) to afford 9u as a colorless oil, 25 mg (50%); IR
819, 748 cmꢀ1
;
1H NMR (400 MHz, CDCl3)
d
1.22 (t, J¼7.2 Hz, 3H),
2.72e2.84 (m, 2H), 3.55 (br s, 1H), 4.15 (q, J¼7.2 Hz, 2H), 5.25e5.28
(m, 1H), 7.42e7.48 (m, 3H), 7.78e7.80 (m, 4H); 13C NMR (100 MHz,
CDCl3)
d 14.2, 43.4, 60.9, 70.4, 123.8, 124.5, 126.0, 126.2, 127.7, 128.0,
128.4, 133.0, 133.3, 140.0, 172.4; GCeMS (EI): m/z 244.1 (Mþ).
4.2.16. Ethyl 3-(benzo[d][1,3]dioxol-5-yl)-3-hydroxypropanoate
(9p).15 Prepared according to general procedure and purified by

612
X.-L. Zou et al. / Tetrahedron 69 (2013) 607e612
Horita, Y.; Inomata, K. Chem. Lett. 2001, 254; (e) Adrian, J. C., Jr.; Snapper, M. L. J.
Org. Chem. 2003, 68, 2143; (f) Sato, K.; Tarui, A.; Kita, T.; Ishida, Y.; Tamura, H.;
Omote, M.; Ando, A.; Kumadaki, I. Tetrahedron Lett. 2004, 45, 5735; (g) Dondoni,
A.; Massi, A.; Sabbatini, S. Chem. Eur. J. 2005, 11, 7110.
5. (a) Fornalczyk, M.; Singh, K.; Stuart, A. M. Org. Biomol. Chem. 2012, 10, 3332; (b)
Wolf, C.; Moskowitz, M. J. Org. Chem. 2011, 76, 6372; (c) Lin, N.; Chen, M.-M.;
Luo, R.-S.; Deng, Y.-Q.; Lu, G. Tetrahedron: Asymmetry 2010, 21, 2816; (d) Ben-
fatti, F.; Cozzi, P. G. Tetrahedron: Asymmetry 2010, 21, 1503; (e) Cozzi, P. G.;
Benfatti, F.; Capdevila, M. G.; Mignogna, A. Chem. Commun. 2008, 3317; (f)
Cozzi, P. G.; Mignogna, A.; Vicennati, P. Adv. Synth. Catal. 2008, 350, 975; (g)
(KBr film): 3600, 3030, 1705, 1600, 1496, 1455, 1300, 1067, 756,
698 cmꢀ1 1H NMR (400 MHz, CDCl3)
2.18 (s, 3H), 2.76e2.91
(m, 2H), 3.34 (br s, 1H), 5.13 (dd, J¼3.3, 9.2 Hz, 1H), 7.25e7.35 (m,
;
d
5H); 13C NMR (100 MHz, CDCl3)
d 30.8, 52.0, 69.9, 125.7, 127.7, 128.6,
142.8, 209.2; GCeMS (EI): m/z 164.0 (Mþ).
4.2.22. 3-Hydroxy-N,N-dimethyl-3-phenylpropanamide (9v).20 IPr
(0.6 mg, 0.0015 mmol) was dissolved in 1.0 mL dry DMF and cooled
ꢀ
ꢀ~
ꢀ
Fernandez-Ibanez, M. A.; Macia, B.; Minnaard, A. J.; Feringa, B. L. Org. Lett. 2008,
to 0 ꢁC, then benzaldehyde (30.6
mL, 0.3 mmol) and N,N-dimethyl-
ꢀ
ꢀ~
ꢀ
10, 4041; (h) Fernandez-Ibanez, M. A.; Macia, B.; Minnaard, A. J.; Feringa, B. L.
ꢀ
ꢀ~
ꢀ
2-(trimethylsilyl)acetamide 8c (72 mg, 0.45 mmol) were loaded via
syringe under N2. Subsequently the reaction solution was stirred at
room temperature until full consume of the benzaldehyde
indicated by TLC, 3 mL 1 N HCl was added at this moment and the
mixture was continue stirred for 0.5 h, then the mixture was
extracted by ethyl acetate (3ꢂ15 mL). The combined organic phase
was washed with saturated sodium bicarbonate and H2O. Organic
phase was dried by anhydrous Na2SO4 and concentrated under
vacuum. The crude product was purified through flash column
chromatography (silica gel, PE/EtOAc, 4:1) to afford 9v as a colorless
oil, 26 mg (45%); IR (KBr film) 3400, 3029, 2922, 1620, 1498, 1450,
Chem. Commun. 2008, 2571; (i) Fernandez-Ibanez, M. A.; Macia, B.; Minnaard,
A. J.; Feringa, B. L. Angew. Chem., Int. Ed. 2008, 47, 1317; (j) Cozzi, P. G. Angew.
Chem., Int. Ed. 2006, 45, 2951.
6. For recent reviews, see: (a) Enders, D.; Balensiefer, T. Acc. Chem. Res. 2004, 37,
534; (b) Zeitler, K. Angew. Chem., Int. Ed. 2005, 44, 7506; (c) Enders, D.; Nie-
meier, O.; Henseler, A. Chem. Rev. 2007, 107, 5606; (d) Marion, N.; Díez-
ꢀ
Gonzalez, S.; Nolan, S. P. Angew. Chem., Int. Ed. 2007, 46, 2988 for other recent
papers, see: (e) Enders, D.; Niemeier, O.; Balensiefer, T. Angew. Chem., Int. Ed.
2006, 45, 1463; (f) Takikawa, H.; Hachisu, Y.; Bode, J. W.; Suzuki, K. Angew.
Chem., Int. Ed. 2006, 45, 3492; (g) Dirocco, D. A.; Oberg, K. M.; Dalton, D. M.;
Rovis, T. J. Am. Chem. Soc. 2009, 131, 10872; (h) Li, G.-Q.; Dai, L.-X.; You, S. L. Org.
Lett. 2009, 11, 1623; (i) DiRocco, D. A.; Rovis, T. J. Am. Chem. Soc. 2011, 133, 10402;
(j) Bugaut, X.; Liu, F.; Glorius, F. J. Am. Chem. Soc. 2011, 133, 8130; (k) Sun, F.-G.;
Sun, L.-H.; Ye, S. Adv. Synth. Catal. 2011, 353, 3134; (l) Wang, X.-B.; Zou, X.-L.; Du,
G.-F.; Liu., Z.-Y.; Dai, B. Tetrahedron 2012, 68, 6498.
1422, 1396, 1260, 1150, 1060, 1025, 758, 700 cmꢀ1
(400 MHz, CDCl3) 2.58e2.72 (m, 2H), 2.94 (s, 3H), 2.98 (s, 3H), 3.96
(br s, 1H), 5.14 (dd, J¼2.9, 9.5 Hz, 1H), 7.26e7.30 (m, 1H), 7.34e7.42
;
1H NMR
7. (a) Song, J. J.; Tan, Z.; Reeves, J. T.; Yee, N. K.; Senanayake, C. H. Org. Lett. 2007, 9,
1013; (b) Du, G. F.; He, L.; Gu, C. Z.; Dai, B. Synlett 2010, 2513.
d
8. (a) Suzuki, Y.; Abu Bakar, M. D.; Muramatsu, K.; Sato, M. Tetrahedron 2006, 62,
4227; (b) Suzuki, Y.; Muramatsu, K.; Yamauchi, K.; Morie, Y.; Sato, M. Tetrahedron
2006, 62, 302; (c) Kano, T.; Sasaki, K.; Konishi, T.; Mii, H.; Maruoka, K. Tetrahedron
Lett. 2006, 47, 4615; (d) Fukuda, Y.; Maeda, Y.; Ishii, S.; Kondo, K.; Aoyama, T.
Synthesis 2006, 589; (e) Fukuda, Y.; Kondo, K.; Aoyama, T. Synthesis 2006, 2649;
(f) Fukuda, Y.; Maeda, Y.; Kondo, K.; Aoyama, T. Synthesis 2006, 1937; (g) Fukuda,
Y.; Maeda, Y.; Kondo, K.; Aoyama, T. Chem. Pharm. Bull. 2006, 54, 397; (h) Zhang,
J.; Du, G.-F.; Xu, Y.-K.; He., L.; Dai, B. Tetrahedron Lett. 2011, 52, 7153.
(m, 4H); 13C NMR (100 MHz, CDCl3)
d 35.3, 37.1, 42.0, 70.4, 125.8,
127.5, 128.5, 143.0, 172.3; GCeMS (EI): m/z 193.1 (Mþ).
Acknowledgements
9. (a) Cai, Z. H.; Du, G. F.; He, L.; Gu, C. Z.; Dai, B. Sy
nthesis 2011, 13, 2073; (b) Cai, Z. H.;
Du, G. F.; Dai, B.; He, L. Synthesis 2012, 44, 694.
This work was supported by the National Natural Science
Foundation of China (No. 21162022) and the Team Innovation
Project of Shihezi University (No. 2011ZRKETD-04).
10. Fan, Y.-C.; Du, G.-F.; Sun, W.-F.; Kang, W.; He, L. Tetrahedron Lett. 2012, 53, 2231.
11. (a) Sun, X.; Ye, S.; Wu, J. Eur. J. Org. Chem. 2006, 4787; (b) Raynaud, J.; Ciolino, A.;
Baceiredo, A.; Destarac, M.; Bonnette, F.; Kato, T.; Gnanou, Y.; Taton, D. Angew.
ꢁ
Chem., Int. Ed. 2008, 47, 5390; (c) Raynaud, J.; Liu, N.; Fevre, M.; Gnanou, Y.;
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