Asymmetric intramolecular aldol reaction mediated by (S)-N-substituted-N- (2-pyrrolidinylmethyl)amine to prepare Wieland-Miescher ketone

Article abstract of DOI:10.3987/COM-10-S(E)119

New or known N-substituted-N-(2-pyrrolidinylmethyl)amine derivatives bearing a variety of alkyl and aryl substituents were easily prepared from N-Boc-proline or N-Boc-N-(2-pyrrolidinylmethyl)amine. The enantioselectivity of the intramolecular asymmetric aldol reaction mediated by a combination of the amine derivative and TFA to prepare Wieland-Miescher ketone was examined. During the examination, optimal amount of TFA in the reaction was identified. The Japan Institute of Heterocyclic Chemistry.

Full text of DOI:10.3987/COM-10-S(E)119

HETEROCYCLES, Vol. 82, No. 2, 2011
1727
HETEROCYCLES, Vol. 82, No. 2, 2011, pp. 1727 - 1737. © The Japan Institute of Heterocyclic Chemistry
Received, 31st Augus, 2010, Accepted, 21st October, 2010, Published online, 2nd November, 2010
DOI: 10.3987/COM-10-S(E)119
ASYMMETRIC INTRAMOLECULAR ALDOL REACTION MEDIATED
BY (S)-N-SUBSTITUTED-N-(2-PYRROLIDINYLMETHYL)AMINE TO
PREPARE WIELAND-MIESCHER KETONE
Yuichi Akahane, Kohei Inomata,* and Yasuyuki Endo
Tohoku Pharmaceutical University, 441 Komatsushima, Aobaku, Sendai
9818558, Japan, Email: inomata@tohokupharm.ac.jp
This paper is dedicated to Professor Dr. Albert Eschenmoser on the occasion of
his 85th birthday.
Abstract – New or known N-substituted-N-(2-pyrrolidinylmethyl)amine deriva-
tives bearing a variety of alkyl and aryl substituents were easily prepared from
N-Boc-proline or N’-Boc-N-(2-pyrrolidinylmethyl)amine. The enantioselectivity
of the intramolecular asymmetric aldol reaction mediated by a combination of the
amine derivative and TFA to prepare Wieland-Miescher ketone was examined.
During the examination, optimal amount of TFA in the reaction was identified.
Wieland-Miescher ketone (2), which was prepared by L-proline-mediated asymmetric intramolecular
aldol reaction of the trione (1), has been a highly useful synthon in total syntheses of a variety of natural
products.1,2 This asymmetric aldol reaction has become known as the Hajos-Parrish-Eder-Sauer-Wiechert
(HPESW) reaction,3 and has been widely recognized to involve an enamine-based mechanism. In the
reaction, a hydrogen bond between an oxygen atom on the cyclohexane and a carboxylic acid in L-proline
has played a very important role to stabilize a transition state to achieve a highly enantioselective
process.4-6
In the area of organocatalysis,7 (S)-2-(pyrrolidinylmethyl)pyrrolidine (4) has been employed as a new
catalyst to achieve highly efficient asymmetric reactions, including intra- and intermolecular aldol
reaction.8 Amine-Brønsted acid catalysis has also been utilized in asymmetric Diels-Alder reaction and
1,4-addition reaction to construct new chiral centers.9,10 However, to our knowledge, there have been few
attempts to use a combination of chiral amine and Brønsted acid in the HPESW reaction.11

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HETEROCYCLES, Vol. 82, No. 2, 2011
Recently, we have reported that a combination of (S)-2-(pyrrolidinylmethyl)pyrrolidine (4) and TFA
successfully mediated the HPESW reaction to afford (R)-Wieland-Miescher ketone [(R)-2] accompanied
with 81% ee.12 The process was characterized by an inversion of enantioselectivity when compared with
the similar reaction mediated by L-Proline. Also, the reaction using 4 without a Brønsted acid afforded
(S)-2 with lower enantioselectivity (Scheme 1). We have also established HPESW reaction utilizing
N-benzyl-N-(2-pyrrolidinylmethyl)amine derivatives in the presence of TFA.13 In the study, we have
observed that steric hindrance around N-benzyl moiety was played an important role to achieve higher
enantioselectivity. From these aspects, chiral amines bearing various N-substituents have been still
required to find more effective mediators. We report herein alternative chiral amine mediators in the
HPESW reaction. Specifically, we attempted to use known and new N-(2-pyrrolidinylmethyl)amine (5)
containing a variety of substituents such as alkyl, cycloalkyl, branched alkyl and arylalkyl (Scheme 1).
O
O
O
O
4 (1.0 equiv.)
TFA (1.5 equiv.)
4 (1.0 equiv.)
4a
4a
DMSO
with lower ee
DMSO
O
O
O
1
1
(S)-2
1
(R)-2
(53% yield, 81% ee)
5e: R1 = cyclohexylmethyl
5f: R1 = diphenylmethyl
5g: R1 = (9-fluorenyl)methyl
1
this work
H
N
5a
5b
: R = Me
N
1
R1
: R = t-Bu
N
N
5c: R1 = cyclohexyl
5d: R1 = i-Pr
H
H
5
4
Scheme 1
Among the amines (5) shown in scheme 1, 5a was prepared from N-cbz-L-Proline according to the known
method reported by Iseki et al.14 Amines (5b8, 5c15) were prepared from N-Boc-L-Proline (6) respectively
in the similar manner reported by Mukaiyama et al.15 Thus, DCC-mediated coupling reaction with 6 and a
corresponding amine, and a following deprotection of Boc-moiety in the presence of TFA yielded amide
(7). Lithium aluminium hydride (LAH) reduction of amide group afforded 5b and 5c respectively. The
other ones (5d,15 5e, 5f16 and 5g) were easily prepared by a simple reductive alkylation of
N’-Boc-N-(2-pyrrolidinylmethyl)amine (8)13 with corresponding carbonyl compounds (9), and a
following acidic deprotection of Boc moiety (Scheme 2).
We first examined to determine the optimal amount of TFA in the HPESW reaction mediated by a chiral
amine. Thus, the effect of TFA quantities on the yield and ee of 2 in the HPSEW reaction, mediated by 4,
was examined in detail. All reactions were carried out with 1.0 equiv of 4 in DMSO at rt in the presence
of TFA over the range of 0 to 170 mol% (Table 1 and Figure 1). Although the yield of 2 revealed almost

HETEROCYCLES, Vol. 82, No. 2, 2011
1729
same level around 50-65% in all cases, the absolute configuration of 2 was inverted from S to R at the
range of 40-50 mol% of TFA. Higher ee was observed upon increasing the amount of TFA, and the
parameter reached to a plateau over 100 mol% of TFA. In the presence of more than 100 mol% of TFA,
longer time was required to complete the reaction. From these results, the optimal amount of TFA to
achieve a high ee was in the range from 100 mol% to 170 mol%. Since the highest ee value was observed
in entry 9, 150 mol% of TFA was selected for further application.
1) DCC, HOBt
R1NH2, rt
LAH
NHR1
5b, 5c
CO2H
N
N
2) TFA
CH2Cl2, rt
THF
reflux
6
Boc
H
(58 ~ 59% from )
O
6
7
O
O
9
H
1) , rt
9e
9d
NH2
5d ~ 5g
N
2) NaBH4
Boc
(42 ~ 64%
MeOH, 0oC
O
O
8
from )
8
3) TFA
CH2Cl2, rt
9f
9g
Scheme 2
Table 1
4 (1.0 equiv.)
TFA (n mol%)
1
2
(R)- or (S)-
DMSO
rt
TFA
(mol %)
0
Time
(h)
10
4
Yield a
Ee b ,c
(%)
-19
-14
-8
Config.d
Entry
(%)
55
55
63
61
63
66
65
60
52
51
2
S
1
2
20
S
3
30
4
S
4
40
4
-1
S
5
50
4
9
R
R
R
R
R
R
6
60
4
17
7
80
4
49
8
100
150
170
16
48
48
77
9
81
10
78
a Isolated yield.
b Determined by HPLC equipped with a chiral stationary phase column.
c Ee of (S)-2 was denoted by a minus sign.
d Absolute configuration of a major enantiomer of 2.

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HETEROCYCLES, Vol. 82, No. 2, 2011
Figure 1. The effects of TFA quantities in the HPESW reaction mediated by amine (4)
Table 2
5 (1.0 equiv.)
TFA (1.5 equiv.)
(R)-2
1
DMSO
rt
Time
Yielda
Eeb
Entry
Amine
(h)
48
9
(%)
44(14)
62
(%)
58
68
68
70
68
50
63
1
2
3
4
5
6
7
5a
5b
5c
5d
5e
5f
24
9
47
67
10
24
14
53
53
5g
55
a Isolated yield.
b The recovery of starting 1 was shown in parentheses.
cDetermined by HPLC equipped with a chiral stationary phase
column.
d Same result in Table 1.
Next, the aldol reactions of 1 using a stoichiometric amount of 5 in the presence of 1.5 equiv. of TFA to
yield (R)-2 were carried out. The results were compiled in Table 2. All of the reactions mediated by 5
afforded (R)-2 in moderate yield. The reaction proceeded slowly in the case of 5a bearing a simple methyl
substituent and the reaction was not completed even after 48 h. Cycloalkyl-substituted derivatives such as
5c and 5e were not also very effective and (R)-2 was obtained in 47% and 53% yield respectively (entries
3 and 5). However, 5b and 5d bearing a tertiary or a secondary branched alkyl substituent respectively
improved the yield of (R)-2 (entries 2 and 4). These results suggested us that steric hindrance on

HETEROCYCLES, Vol. 82, No. 2, 2011
1731
N-substituents in 5 obviously affected the reactivity but not greatly improved the enatioselectivity. In
comparison with entries 6 and 7, the reaction mediated by N-(9-fluorenyl)methyl derivative (5g) revealed
slightly higher ee than the case of diphenylmethyl one (5f). This result suggested that a planarity and a
conformationally restriction of two benzene rings might be very important role to the enatioselectivity. In
the previous report, we described that the ammonium moiety, which was produced from an amino
substituent and a Brønsted acid, stabilized a transition state by hydrogen bonds between a mediator and a
substrate.12 Since the present mediators bearing various N-substituents revealed the slightly lower ee than
the case of previous N-benzyl derivatives,13 the stabilization of a transition state was due to the
circumstance around the ammonium moiety. Thus, the mediators substituted by a bulky group directly
such as 5b-5g may inhibit the formation of strong hydrogen bonds to stabilize a favor transition state.
These aspects suggested us that N-substituents such as a benzyl group having both a moderate steric
hindrance and a moderate planarity were a very important structure to achieve higher ee in the HPESW
reaction.
In conclusion, we have established a procedure to prepare N-(2-pyrrolidinylmethyl)amine derivatives (5)
bearing a variety of alkyl and aryl substituents. We also have established a new chiral route to provide
(R)-Wieland-Miescher ketone [(R)-2] by using the combination of synthetic 5 and TFA. Furthermore, we
have determined the optimal amount of TFA in HPESW reaction mediated by a chiral amine. These
results may enable the creation of efficient organocatalysts for a wide variety of asymmetric reactions.
Further work on a detail of the reaction mechanism and the development of a more efficient catalyst for
the reactions is currently in progress.
EXPERIMENTAL
1
Melting points are uncorrected. IR spectra were recorded on a JASCO-FT-IR-5000 spectrometer. H
13
13
NMR spectra and C NMR spectra were recorded on a JEOL-AX-400 (1H 400 MHz, C 100 MHz)
spectrometer and calibrated using trimethysilane as the internal standard. Mass spectra were recorded on a
JEOL-DX-303 or a JEOL-JMS-MS700 spectrometer. Enantiomeric excesses were determined on a
Waters-HPLC 600 instrument equipped with a chiral stationary phase column. Optical rotations were
measured with a JASCO-DIP-370 digital polarimeter.
(S)-N-t-Butyl-N-(2-pyrrolidinylmethyl)amine (5b)
To a stirred solution of N-Boc-L-Proline (6) 5.0 g (23.3 mmol) in CH2Cl2 (50 mL) were added DCC 4.9 g
(23.8 mmol) and 1-hydroxybenzotriazole (HOBt) 3.2 g (23.8 mmol) at rt. After stirring at the same
temperature for 30 min, t-butylamine 1.7 g (23.3 mmol) was added and the mixture was further stirred at
rt for 24 h. The mixture was filtered through a Celite pad and the filtrate was washed with saturated
aqueous NaHCO3 and brine. After drying (Na2SO4), the solvent was removed under reduced pressure to

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HETEROCYCLES, Vol. 82, No. 2, 2011
afford crude product. To the stirred solution of the crude product in CH2Cl2 (70 mL) was added TFA 17.7
mL (233 mmol) at rt and the mixture was stirred at the same temperature for 10 h. The mixture was
extracted with H2O. The combined aqueous layer was basified by 10% aqueous NaOH and was extracted
with CH2Cl2. The combined organic layer was dried (Na2SO4) and the solvent was removed under
reduced pressure to afford crude 7. To a stirred suspension of LAH 1.3 g (35 mmol) in THF (70 mL) was
added a solution of 7 in THF (20 mL) at 0 oC. The mixture was further heated under reflux for 24 h. 10%
aqueous NaOH (14 mL) was carefully added to the mixture at 0 oC and the mixture was stirred at rt for 2
h. The mixture was filtered through a Celite pad and the filtrate was evaporated under reduced pressure.
The residue was chromatographed (CHCl3/MeOH/NH4OH =15/1/0.1) to afford 5b 2.1 g (58% from 6) as
a yellow oil.
27
25
[]D +11.8 (c 1.00, CHCl3), [lit.,8a []D +12.0 (c 1.98, CHCl3)]; IR (film) cm-1 3429, 2980, 1407;
1H-NMR (400 MHz, CDCl3) 1.09 (9H, s), 1.29-1.37 (1H, m), 1.65-1.81 (4H, m), 1.84-1.92 (1H ,m),
2.47 (1H, dd, J = 8.4 Hz, 11.2 Hz), 2.55 (1H, dd, J = 4.8 Hz, 11.2 Hz), 2.84-2.94 (2H, m), 3.11-3.17 (1H,
13
m); C-NMR (100 MHz, CDCl3) 25.5, 28.9, 29.7, 46.3, 47.7, 49.9, 59.0; EIMS (m/z) 156 (M+), 70
(100%); HRMS calcd. for C9H20N2 156.1626, found 156.1623.
(S)-N-Cyclohexyl-N-(2-pyrrolidinylmethyl)amine (5c)
In the similar manner described for 5b, 5c was obtained by the use of cyclohexylamine instead of t-butyl-
amine.
28
24
Yield 59% (yellow oil); []D +9.8 (c 1.00, EtOH), [lit.,15 []D +10.3 (c 1.01, EtOH)]; IR (film)
1
cm-1 3401, 2931, 2856, 1408; H- NMR (400 MHz, CDCl3) 1.03-1.34 (6H, m), 1.60-1.63 (1H, m),
1.67-1.78 (6H, m), 1.84-1.91 (3H, m), 2.37-2.43 (1H, m), 2.49 (1H, dd, J = 8.8 Hz, 11.6 Hz), 2.66 (1H,
dd, J = 4.8 Hz, 11.2 Hz), 2.86-2.92 (2H, m), 3.19 (1H, ddd, J = 4.8 Hz, 7.4 Hz, 15.6 Hz); 13C-NMR (100
MHz, CDCl3) 25.0, 25.6, 29.7, 33.4, 33.4, 46.3, 52.0, 57.0, 58.5; EIMS (m/z) 182 (M+), 70 (100%);
HRMS calcd. for C11H22N2 182.1783, found 182.1786.
(S)-N-Isopropyl-N-(2-pyrrolidinylmethyl)amine (5d)
To a stirred solution of 813 3.5 g (17.5 mmol) in acetone (30 mL) at rt. After stirring at the same
temperature for 8 h, the solvent was removed under reduced pressure. The residue was dissolved to
MeOH (30 mL) and NaBH4 333 mg (8.75 mmol) was added to the mixture as a small portion over 10 min
o
o
at 0 C. After stirring at 0 C for 7 h, the solvent was removed under reduced pressure. The residue was
dissolved to AcOEt and the mixture was washed with saturated aqueous NaHCO3 and brine. The organic
layer was dried (Na2SO4) and the solvent was removed under reduced pressure. The residue was
dissolved to CH2Cl2 (70 mL) and TFA 13 mL (175 mmol) was added to the mixture at rt. After stirring at
the same temperature for 15 h, the mixture was extracted with H2O. The combined aqueous layer was

HETEROCYCLES, Vol. 82, No. 2, 2011
1733
basified by 10% aqueous NaOH and the mixture was extracted with CH2Cl2. The combined organic layer
was dried (Na2SO4) and the solvent was removed under reduced pressure. The residue was
chromatographed (CHCl3/MeOH/NH4OH =10/1/0.1) to afford 5d 1.6 g (64% from 8) as a yellow oil.
28
26
[]D +16.0 (c 1.00, MeOH), [lit.,15 []D +16.5 (c 1.07, EtOH)]; IR (film) cm-1 3401, 2977, 1411;
1H-NMR (400 MHz, CDCl3) 1.05 (3H, d, J = 4.3 Hz), 1.06 (3H, d, J = 4.3 Hz), 1.28-1.37 (1H, m),
1.68-1.76 (4H, m), 1.84-1.91 (1H, m), 2.46 (1H, dd, J = 4.8 Hz, 11.4 Hz), 2.63 (1H, dd, J = 4.8 Hz, 11.4
13
Hz), 2.75-2.81 (1H, m), 2.88-2.92 (2H, m), 3.20 (1H, ddd, J = 4.8 Hz, 7.4 Hz, 15.9 Hz); C-NMR (100
MHz, CDCl3) 23.0, 25.7, 29.8, 46.4, 48.8, 52.9, 58.5; EIMS (m/z) 142 (M+), 70 (100%); HRMS calcd.
for C8H18N2 142.1470, found 142.1437.
(S)-N-Cyclohexylmethyl-N-(2-pyrrolidinylmethyl)amine (5e)
To a stirred solution of 8 3.5 g, (17.5 mmol) in dichloromethane (35 mL) was added cyclohexane-
carboxaldehyde 2.3 mL (19.3 mmol) at rt. After stirring at the same temperature for 9 h, the solvent was
removed under reduced pressure. The residue was dissolved to MeOH (35 mL) and NaBH4 333 mg (8.75
mmol) was added to the mixture as a small portion over 10 min at 0 oC. After stirring at 0 oC for 7 h, the
solvent was removed under reduced pressure. The residue was dissolved to AcOEt and the mixture was
washed with saturated aqueous NaHCO3 and brine. The organic layer was dried (Na2SO4) and the
solvent was removed under reduced pressure. The residue was dissolved to CH2Cl2 (70 mL) and TFA 13
mL (175 mmol) was added to the mixture at rt. After stirring at the same temperature for 15 h, the
mixture was extracted with H2O. The combined aqueous layer was basified by 10% aqueous NaOH and
the mixture was extracted with CH2Cl2. The combined organic layer was dried (Na2SO4) and the solvent
was removed under reduced pressure. The residue was chromatographed (CHCl3/MeOH/NH4OH
=10/1/0.1) to afford 5e 1.6 g (47% from 8) as a yellow oil.
28
1
[]D +12.1 (c 1.00, MeOH); IR (film) cm-1 3400, 2924, 2851, 1409; H-NMR (400 MHz, CDCl3)
0.85-0.94 (2H, m), 1.10-1.36 (4H, m), 1.40-1.49 (1H, m), 1.65-1.78 (9H, m), 1.83-1.91 (1H, m), 2.44
(2H, dd, J = 2.4 Hz, 6.8 Hz), 2.49 (1H, dd, J = 8.2 Hz, 11.6 Hz), 2.59 (1H, dd, J = 4.8 Hz, 11.8Hz),
13
2.85-2.95 (2H, m), 3.18-3.25 (1H, m); C-NMR (100 MHz, CDCl3) 25.6, 26.0, 26.6, 29.7, 31.3, 37.8,
46.4, 55.3, 56.9, 58.2; EIMS (m/z) 196 (M+), 70 (100%); HRMS calcd. for C12H24N2 196.1939, found
196.1916.
(S)-N-Diphenylmethyl-N-(2-pyrrolidinylmethyl)amine (5f)
In the smilar manner described for 5e, 5f was obtained by the use of benzophenone instead of
cyclohexanecarboxaldehyde.
20
25
Yield 42% (yellow oil); []D +19.2 (c 0.84, MeOH), [lit.,16 []D +20.0 (c 1.0, MeOH)]; IR (film)
1
cm-1 3283, 2956, 2869, 1452, 1405; H-NMR (400 MHz, CDCl3) 1.30-1.37 (1H, m), 1.65-1.92 (3H,

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HETEROCYCLES, Vol. 82, No. 2, 2011
m), 2.48 (1H, dd, J = 8.4 Hz, 11.6 Hz), 2.59 (1H, dd, J = 4.8 Hz, 11.8 Hz), 2.87-2.91 (2H, m), 3.27 (1H,
ddd, J = 4.8 Hz, 7.2 Hz, 11.7 Hz), 4.81 (1H, s), 7.19-7.21 (2H, m), 7.29 (4H, dt, J = 2.0 Hz, 7.2 Hz),
7.38-7.41 (4H, m); 13C-NMR (100 MHz, CDCl3) 25.4, 29.5, 46.2, 52.8, 58.5, 67.6, 126.9, 127.2, 128.4,
144.0; EIMS (m/z) 266 (M+), 70 (100%); HRMS calcd. for C18H22N2 266.1783, found 266.1787.
(S)-N-(9-Fluorenyl)-N-(2-pyrrolidinylmethyl)amine (5g)
In the smilar manner described for 5e, 5g was obtained by the use of 9-fluorenone instead of
cyclohexanecarboxaldehyde.
21
Yield 48% (yellow oil); []D -8.6 (c 1.00, CHCl3); IR (film) cm-1 3285, 2926, 2871, 144.7, 1403;
1H-NMR (400 MHz, CDCl3) 1.17-1.26 (1H, m), 1.61-1.68 (2H, m), 1.72-1.80 (1H, m), 2.08 (2H, brs),
2.22 (1H, dd, J = 8.0 Hz, 11.8 Hz), 2.34 (1H, dd, J = 4.8 Hz, 11.8 Hz), 2.82-2.86 (2H, m), 3.09-3.15 (1H,
m), 4.96 (1H, s), 7.33-7.39 (4H, m), 7.59-7.62 (2H, m), 7.69-7.71 (2H, m); 13C-NMR (100 MHz, CDCl3)
25.4, 29.3, 46.2, 48.6, 58.9, 63.4, 119.8, 124.7, 127.2, 127.8, 140.6, 145.6; EIMS (m/z) 264 (M+), 70
(100%); HRMS calcd. for C18H20N2 264.1626, found 264.1624.
The effect of quaintities of TFA in the HPESW reaction
To a stirred solution of the trione (1) 147 mg (0.75 mmol) in DMSO (1.5 mL) was added the amine (4)
121 L (0.75 mmol) and TFA 86 L (1.1 mmol) at rt. The reaction mixture was stirred at rt for 48 h, then
diluted with ethyl acetate (AcOEt), washed with saturated aqueous NaHCO3 and brine, and dried
(MgSO4). The solvent was removed under reduced pressure. The crude product was chromatographed on
silica gel (AcOEt/CH2Cl2/hexane = 1/1/4) to afford (R)-2 70 mg (52%) as a pale yellow oil. The optical
purity was determined to be 81% ee by HPLC with a chiral stationary phase. HPLC conditions: Chiralcel
OD, 2-propanol/hexane = 1/10 (v/v), flow rate 1.0 mL/min, detected at 254 nm, tR = 14.6 min for (S)-2,
15.7 min for (R)-2. The results in Table 1 were obtained by the same manner changing the amount of
TFA in the range from 0 to 170 mol%.
Typical procedure of HPESW reaction mediated by chiral amine (5)
To a stirred solution of 5d 203 mg (0.70 mmol) and TFA 86 L (1.13 mmol) in DMSO (1.5 mL) was
added 1 147 mg (0.75 mmol) at rt. After stirring at the same temperature for 9 h, the mixture was diluted
with AcOEt and the mixture was washed with saturated aqueous NaHCO3 and brine. The organic layer
was dried (Na2SO4) and the solvent was removed under reduced pressure. The residue was
chromatographed (AcOEt/CH2Cl2/hexane = 1/1/4) to afford (R)-2 84 mg (67%) as a pale yellow oil. The
optical purity was determined to be 70% ee by the same manner described above.
[]D25 -69.1: 70% ee (c 1.00, benzene), [lit., [(S)-2],3l []D25 +100 (c 1.40, benzene)]; IR (film) cm-1
1714, 1668; 1H-NMR (400 MHz, CDCl3) 1.46 (3H, s), 1.67-1.78 (1H, m), 2.10-2.19 (3H, m), 2.44-2.53
13
(4H, m), 2.68-2.77 (2H, m), 5.87 (1H, s); C-NMR (100 MHz, CDCl3) 22.8, 23.2, 29.6, 31.7, 33.5,

HETEROCYCLES, Vol. 82, No. 2, 2011
1735
37.6, 50.5, 125.8, 165.8, 198.2, 211.0; EIMS (m/z) 178 (M+, 100%); HRMS calcd. for C11H14O2 178.0992,
found 178.0988.
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