Chiral bipyridine-copper(I) complex-catalyzed enantioselective allylic oxidation of cyclic alkenes

Article abstract of DOI:10.1016/S0957-4166(01)00160-4

Chiral copper(I)-bipyridine complexes were prepared and used as catalysts in the enantioselective allylic oxidation of cyclic alkenes with tert-butyl perbenzoate. The yields ranged from moderate to good and enantioselectivities up to 70% were observed.

Full text of DOI:10.1016/S0957-4166(01)00160-4

TETRAHEDRON:
ASYMMETRY
Pergamon
Tetrahedron: Asymmetry 12 (2001) 1007–10013
Chiral bipyridine–copper(I) complex-catalyzed enantioselective
†
allylic oxidation of cyclic alkenes
Wing-Sze Lee, Hoi-Lun Kwong,* Hoi-Ling Chan, Wing-Wai Choi and Lai-Yuen Ng
Department of Biology and Chemistry, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon, Hong Kong SAR, China
Received 15 February 2001; accepted 2 April 2001
Abstract—Chiral copper(I)–bipyridine complexes were prepared and used as catalysts in the enantioselective allylic oxidation of
cyclic alkenes with tert-butyl perbenzoate. The yields ranged from moderate to good and enantioselectivities up to 70% were
observed. © 2001 Elsevier Science Ltd. All rights reserved.
3
0
1
. Introduction
recently by Ko cˇ ovsk y´ et al. We recently reported the
synthesis of chiral bipyridine alcohols 1–6 and their use
in the asymmetric diethylzinc addition reaction, in
The copper-catalyzed allylic oxidation of olefins with
peresters has been the subject of numerous synthetic
and mechanistic investigations.
reaction, unactivated olefins can be functionalized into
chiral allylic carboxylates, which are important interme-
diates in the synthesis of biologically active compounds.
Early attempts toward asymmetric allylic oxidation
3
1
which excellent enantioselectivities were obtained. In
an extension of the synthetic scope of this class of
ligand, we report herein the use of bipyridine alcohols
1–8 in the copper-catalyzed asymmetric allylic oxida-
tion of olefins with tert-butyl perbenzoate (Scheme 1).
1–7
Through this useful
8
using Cu complexes of (+)-a-ethyl camphorate, chiral
9
9
Schiff bases and optically active amino acids gave
poor enantioselectivities. In the last decade better
results have started to appear. Several groups have
reported the use of oxazoline-containing ligands in the
Cu-catalyzed allylic oxidation of alkenes, which gave
2. Results and discussion
Ligands 1–6 were prepared in good yields according to
31
the previously reported procedures. Ligands 7 and 8
were prepared by cross coupling of bromopyridyl alco-
hols 9 and 10 with 2-pyridylzinc chloride using catalytic
amounts of tetrakis(triphenylphosphine)palladium(0)
10–19
good enantioselectivity.
However, a universal prob-
lem that still remains is the very poor reaction rate. The
reactions sometimes require close to a month to reach
completion. Also, some ligands are not stable enough
to withstand the harsh oxidizing environment of the
reaction. It is therefore a challenge to develop new
ligand systems for this reaction.
31,32
catalyst (Scheme 2).
Ligands 7 and 8 were isolated
in 73 and 75% yield, respectively.
Having prepared these C - and C -symmetric bipyridine
1 2
ligands, they were tested in the Cu-catalyzed allylic
oxidations of cyclohexene. The reactions were carried
Chiral bipyridine ligands have received extensive atten-
tion in asymmetric catalysis in the past 10 years. They
were reported to have applications in several asym-
metric reactions, such as Cu-catalyzed cyclopropana-
out with
6
mol% of 1–8 and
6
5
mol% of
[Cu(CH CN)
]PF as catalyst at room temperature in
3
4
acetonitrile. All reactions were allowed to proceed until
the catalyst turnover slowed or stopped. The results are
summarized in Table 1. Ligand 1–CuPF complex gave
cyclohex-2-enyl benzoate as the product with 57% iso-
lated yield and 93% conversion after 48 h (entry 1). The
enantiomeric excess (e.e.) of the product was 52%. The
2
0–26
27
tion,
catalyzed allylic substitution.
Cu-catalyzed allylic oxidations have also been obtained
Zn-catalyzed allylic alkylation, and Pd-
6
28,29
Very good results for
other ligand–CuPF complexes were found to be active
6
catalysts (entries 6–9 and 14–16). Isolated yields were
from moderate to good and the enantioselectivities
were varied with product e.e.s ranging between 0 and
*
Corresponding
bhhoik@cityu.edu.hk
author.
Fax:
(852)-2788-7406;
e-mail:
†
Dedicated to Professor K. Barry Sharpless for the occasion of his
0th birthday.
6
65%. In general, reactions with C -symmetric ligands
2
0
957-4166/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0957-4166(01)00160-4

1
008
W.-S. Lee et al. / Tetrahedron: Asymmetry 12 (2001) 1007–1013
Scheme 1.
were slightly faster than those with C -symmetric lig-
10–13). Variation of Cu salts had a great effect on both
the enantioselectivity and reactivity. For 1, the best
result was achieved with Cu(OTf) as the copper source.
The reaction took 48 h and gave product with 95%
conversion and 58% e.e. (entry 3). [Cu(CH CN) ]ClO
4
gave slightly lower conversion and e.e. By using either
CuBr or CuCl as the metal precursor, the reaction
occurred slowly and no enantioselectivity was induced
by the catalyst (entries 4 and 5).
1
ands. The C -ligands gave (R)-allylic benzoates as the
2
major product. Interestingly, the absolute configura-
tions of the major products obtained for the C -sym-
1
metric ligands 5 and 7 were opposite to their
3
4
corresponding C -symmetric ligands 1 and 3. This sug-
2
gests that the transition states of the reactions pro-
moted by complexes of 1 and 3 may be diffe-
rent from those of the reactions promoted by com-
plexes of 5 and 7. Similar observations were also
17
reported in the literature. Of the four C -symmetric
For 5, different trends were observed. The highest
enantioselectivity (65% e.e.) was still obtained with
[Cu(CH CN) ]PF (entry 9). The highest reaction rate
1
ligands, the best result was achieved with 5. It gave 65%
e.e. and 65% conversion after 48 h (entry 9). In con-
trast, 6 and 8 gave no asymmetric induction (entries 14
and 16).
3
4
6
was observed with [Cu(CH CN) ]ClO (entry 10),
3
4
4
which gave 74% conversion after 48 h. However,
CuOTf, CuBr or CuCl as the precursor gave very poor
product e.e.s and/or conversions (entries 11–13). Pre-
liminary rate studies indicated that the rate of the
With 1 and 5 being the best ligands, reaction conditions
were optimized by varying the Cu salts (entries 2–5 and
Scheme 2.

W.-S. Lee et al. / Tetrahedron: Asymmetry 12 (2001) 1007–1013
1009
Table 1. Asymmetric allylic oxidation of cyclohexene promoted by chiral bipyridine copper(I) complexes
Entry
Ligand L
Catalyst
Time (h)
Conversion (%)a
Yield (%)b
E.e. (%)c
1
2
3
4
5
6
7
8
9
1
1
1
1
1
2
3
4
5
5
5
5
5
6
7
8
[Cu(CH CN) ]PF
6
48
48
48
48
60
60
48
48
48
48
72
48
48
72
96
72
93
81
95
73
63
63
59
57
65
74
54
14
0
57
70
63
78
71
79
44
47
52 (R)
47 (R)
58 (R)
0
3
4
[Cu(CH CN) ]ClO
3
4
4
CuOTf
CuCl
CuBr
0
[Cu(CH CN) ]PF
22 (R)
31 (R)
30 (R)
65 (S)
64 (S)
16 (S)
3
4
6
6
6
6
[Cu(CH CN) ]PF
3
4
[Cu(CH CN) ]PF
3
4
[Cu(CH CN) ]PF
43
38
77
3
4
10
11
12
13
14
15
16
[Cu(CH CN) ]ClO
3
4
4
CuOTf
CuCl
CuBr
N.D.d
N.D.d
66
N.D.
d
d
N.D.
[Cu(CH CN) ]PF
42
73
40
0
3
4
6
6
6
[Cu(CH CN) ]PF
80
68
8 (S)
0
3
4
[Cu(CH CN) ]PF
3
4
a
b
c
Conversions were calculated based on the ratio of tert-butyl perbenzoate and product obtained from GC.
Yields were isolated and were calculated based on conversion.
Determined by HPLC analysis using a chiral OD column (hexane/propan-2-ol=1000/1). Absolute configuration was determined by comparing
1
7
the order of elution with samples of known configurations.
d
Not determined.
reaction is affected by the concentration of the copper
catalyst but not the alkene or tert-butyl perbenzoate
concentration. Work is in progress to understand the
kinetics and mechanism of the reaction.
observed for ligand 5 using either [Cu(CH CN) ]PF or
3
4
6
[Cu(CH CN) ]ClO , (entries 5 and 6). However, using
3
4
4
CuOTf or CuBr as the metal source gave poorer results
in terms of enantioselectivity or conversion (entries 7
and 8).
Ligands 1 and 5 were also found to catalyze the allylic
oxidation of cyclopentene. The results of this study are
summarized in Table 2. For the ligand 1, the best
enantioselectivity of 61% was achieved with CuBr
The absolute configurations of the products obtained
for C -bipyridine 1 (R) and C -bipyridine 5 (S) were
2
1
again opposite. From the above results, it seems that
the effect of the copper salt is strongly dependent on
the substrate and the specific ligand. The reactions
promoted with [Cu(CH CN) ]PF were generally faster
(
entry 4), which is in sharp contrast to the equivalent
reaction with cyclohexene. The reactions with different
copper salts proceeded at comparable rates (entries
3
4
6
1–4). Similar rates and enantioselectivities were
than those with other Cu salts.
Table 2. Asymmetric allylic oxidation of cyclopentene promoted by copper(I) complexes of chiral bipyridine ligands 1 and 5
Entry
Ligand L
Catalyst
Time (h)
Conversion (%)a
Yield (%)b
E.e. (%)c
1
2
3
4
5
6
7
8
1
1
1
1
5
5
5
5
[Cu(CH CN) ]PF
6
48
48
48
48
48
48
48
144
88
81
90
81
78
84
81
37
64
70
88
59
83
87
82
53
26 (R)
38 (R)
32 (R)
61 (R)
56 (S)
55 (S)
29 (S)
54 (S)
3
4
[Cu(CH CN) ]ClO
3
4
4
4
CuOTf
CuBr
[Cu(CH CN) ]PF
3
4
6
[Cu(CH CN) ]ClO
3
4
CuOTf
CuBr
a
Percent conversions were calculated based on the ratio of tert-butyl perbenzoate and product obtained from GC.
Yields were isolated and were calculated based on conversion.
b
c
Determined by HPLC analysis using a chiral OD column (hexane/propan-2-ol=1000/1). Absolute configuration was determined by comparing
1
7
the order of elution with samples of known configurations.

1
010
W.-S. Lee et al. / Tetrahedron: Asymmetry 12 (2001) 1007–1013
Table 3. Asymmetric allylic oxidation of cycloheptene and cyclooctene promoted by copper(I) complexes of chiral bipyridine
ligands 1 and 5
Entry
Ligand L
Substrate
Conversion (%)a
Yield (%)b
E.e. (%)
1
2
3
4
1
1
5
5
n=1
n=2
n=1
n=2
79
35
71
31
62
72
69
81
61 (R)c
d
70 (R)
c
21 (S)
12 (S)
d
a
Percent conversions were calculated based on the ratio of tert-butyl perbenzoate and product obtained from GC.
Yields were isolated and were calculated based on conversion.
b
c
Determined by HPLC analysis using a chiral OJ column (hexane/propan-2-ol=1000/1). Absolute configuration was determined by comparing
3
0
the order of elution with samples of known configurations.
d
Determined by HPLC analysis using a chiral OD column (hexane/propan-2-ol=1000/1). Absolute configuration was determined by comparing
the order of elution with that of products from cyclohexene and cyclopentene.
With the use of 1 or 5 and [Cu(CH CN) ]PF as
and 13 and 14 were prepared by similar methods using
palladium(0)-catalyzed cross coupling of bromopyridyl
alcohols 9 and 10 with phenylboronic acid (Scheme
3
4
6
catalyst under the optimized reaction conditions as
cyclohexene, we also examined the oxidation of cyclo-
heptene and cyclooctene (Table 3). In the case of
cycloheptene, conversions between 79 and 71% for 1
and 5, respectively, were obtained after 4 days (entries
31,32
4).
Ligands 11–14 were all active in catalyzing
allylic oxidation. However, all of them gave very low
product e.e.s of <5%. The results seem to suggest that
1–8 are not functioning as N,O-ligands.
1
and 3). However, reaction promoted by 1 gave higher
enantioselectivity than 5 (61 and 21% e.e. for 1 and 5,
respectively). In the case of cyclooctene, the reaction
proceeded at a much lower rate than other substrates.
Ligands 1 and 5 only gave 35 and 31% conversion,
respectively, after 4 days (entries 2 and 4). The enan-
tioselectivity obtained with 1 was again markedly
greater than 5 (70 and 12% e.e. for 1 and 5, respec-
tively). Additionally, the absolute configurations of the
products achieved with 1 and 5 were opposite to each
other.
With these observations and the absolute configura-
tions of the products formed by the C - and C -sym-
metric ligands, we proposed the models shown in
1
2
Although bipyridine ligands 1–8 can function as N,N-
bidentate ligands, they could also function as N,O-
bidentate ligands. A previous study using 1–6 showed
that they probably function as N,O-ligands in the alkyl-
31
ation of aldehydes. In order to reveal more details of
the nature of the active catalytic species, we prepared
the phenyl substituted pyridylalcohols 11–14 and com-
pared their reactivity with 1–8, respectively (Scheme 3).
The synthesis of 11 and 12 were reported previously
Scheme 3.
Scheme 4.

W.-S. Lee et al. / Tetrahedron: Asymmetry 12 (2001) 1007–1013
1011
Schemes 5 and 6, in which ligands 1 and 5, respectively,
were used with cyclohexene, to explain the results here.
The first set of models for 1 (Scheme 5) was similar to
still needs further investigation and we are continuing
our efforts to find other, better catalysts for this
reaction.
those proposed based on chiral C -symmetric N,N-
2
1
1
bidentate and N,N,N-tridentate ligand–copper com-
1
2
plex catalysts. In these models, the favored transition
states are depicted with the cyclohexenyl and benzoate
groups positioned to minimize interaction with the
bulky pendant group of the bipyridine ligand. In the
second set of models, for 5 (Scheme 6), we proposed
that the removal of a bulky pendant group from one
side of the ligand leads to the change in the coordina-
tion of the cyclohexenyl group. In order to further
minimize interaction with the pendant group of the
ligand, the opposite prochiral face then coordinates to
the metal center.
3. Experimental
3
.1. General methods
Acetonitrile was distilled under N2 over calcium
hydride. Chemicals were of reagent-grade quality and
were obtained commercially. Ligands 1–6 and 9–12
31
were prepared according to the literature. Infrared
−
1
spectra, in the range 500–4000 cm , were recorded as
KBr plates on a Perkin–Elmer model 1600 FTIR spec-
1
13
trometer. H and C NMR spectra were recorded on a
Varian 300 MHz Mercury instrument. Positive-ion
FAB mass spectra were recorded on a Finnagin MAT
5 spectrometer as 3-nitrobenzylalcohol matrices. Elec-
tron-ionization mass spectra were recorded on a
Hewlett–Packard 5890II GC instrument coupled with a
970 mass selective detector. Elemental analyses were
performed on a Vario EL elemental analyzer. Optical
rotation was measured by a JASCO DIP-370 digital
polarimeter. Melting points were measured by an elec-
trothermal digital melting point apparatus. Reactions
were monitored by GC using a Hewlett–Packard
In conclusion, we have successfully demonstrated that
1
–8 are good catalytic ligands for the copper-catalyzed
allylic oxidation of olefins. In the case of cyclooctene,
we achieved an e.e. of 70%. Comparison of the enan-
tioselectivity of the reactions of 11–14 with those of
9
1
–8, indicates that 1–8 do not function as N,O-biden-
5
tate ligands in the allylic oxidation reaction. However,
the exact nature of the coordination of these ligands
5
890II GC instrument with an Ultra 2-crosslinked 5%
PhMesilcone (25 m×0.2 mm×0.33 mm) column.
3
.2. General procedures for the synthesis of bipyridine
ligands 7 and 8
A solution of 2-bromopyridine (1.1 g, 7 mmol) in THF
(
30 mL) was cooled to −78°C and treated slowly with a
solution of n-butyllithium in hexanes (2.5 M, 2.8 mL, 7
mmol). The resulting red–brown solution was stirred at
this temperature for 30 min and was then transferred by
cannula into a cold (−78°C) solution of dry ZnCl (0.96
2
g) in THF (20 mL) (ZnCl was used after fusion by
2
flame-drying under reduced pressure). The color of the
solution remained at this temperature. After warming
to rt, the mixture was stirred until the color changed to
yellow–brown. This mixture was transferred into a
stirred solution of bromopyridyl alcohol 9 or 10 (3.5
mmol) and of tetrakis(triphenylphosphine)palladium(0)
Scheme 5.
(
0.4 mmol, 0.4 g) in THF (20 mL). After stirring for 16
h at rt, saturated aqueous NaHCO3 (100 mL) was
added, and the layers were separated. The aqueous
layer was extracted with CH Cl (3×50 mL) and the
2
2
combined organic layers were washed with brine (50
mL), dried over Na SO and filtered. The solvent was
2
4
removed under reduced pressure to give crude product,
which was purified by column chromatography. The
1
13
product was then characterized by IR, H NMR,
C
NMR, CHN and MS analysis.
3
.2.1. Bipyridine ligand 7. The above general procedure
was followed. Usual work-up gave 0.79 g (73%) of 7:
25
mp 76.5–78.5°C; [h] =−60.0 (c 0.52, CCl ); IR (KBr):
3355.3 s, 1572.1 s, 1559.6 s; H NMR (300 MHz,
D
4
1
Scheme 6.

1
012
W.-S. Lee et al. / Tetrahedron: Asymmetry 12 (2001) 1007–1013
CDCl ): l 0.50 (s, 3H), 1.03 (s, 3H), 1.04 (s, 3H), 1.19
3.3.2. Pyridyl alcohol 14. Following the above proce-
dure, using bromopyridyl alcohol 10 and usual work-up
3
(
m, 1H), 1.39 (m, 1H), 1.52 (m, 1H), 1.80–1.95 (m, 2H),
.26–2.44 (m, 2H), 6.10 (s, 1H), 7.32 (m, 1H), 7.56 (d,
25
2
1
8
2
8
1
3
gave 0.74 g (44%) of 14: mp 58–60°C; [h] =−35.4 (c
D
1
H, J=7.7 Hz), 7.70–7.80 (m, 2H), 8.20–8.40 (d, 2H),
0.52, CCl ); IR (KBr): 3422.2 s, 1566.7 s; H NMR
4
1
3
.68 (m, 1H); C NMR (75 MHz, CDCl ): l 17.18,
(CDCl ): l 1.28 (s, 3H), 1.30 (s, 3H), 1.20–1.40 (m, 1H),
3
3
2.25, 24.39, 29.30, 32.50, 41.97, 46.00, 48.79, 51.93,
3.72, 118.58, 120.66, 122.99, 123.53, 136.08, 136.67,
48.90, 152.80, 155.42, 161.46; MS (EI) m/z (rel. int.):
1.90–2.25 (m, 6H), 2.50–2.70 (m, 1H), 4.98 (s, 1H),
7.35–7.50 (m, 4H), 7.62 (d, 1H, J=7.7 Hz), 7.75 (t, 1H,
13
J=7.7 Hz), 8.01 (d, 2H, J=6.9 Hz); C NMR
+
08 (M , 7), 280 (32), 227 (88), 211 (base), 170 (30), 155
(CDCl ): l 23.52, 25.05, 25.77, 27.80, 29.87, 38.95,
3
(
9
99). Anal. calcd for C H N O: C, 77.92; H, 7.79; N,
.09. Found: C, 77.67; H, 7.84; N, 9.27%.
40.13, 53.54, 78.74, 118.01, 118.17, 126.63, 128.44,
2
0
24
2
128.83, 137.06, 138.64, 154.96, 165.97; MS (EI) m/z
+
(
rel. int.): 293 (M , 29), 265 (52), 210 (70), 182 (64), 169
3
.2.2. Bipyridine ligand 8. The above procedure was
(65), 154 (base). Anal. calcd for C H NO: C, 81.87;
H, 7.90; N, 4.77. Found: C, 82.35; H, 8.25; N, 4.26%.
20 23
followed. Usual work-up gave 0.77 g (75%) of 8: mp
2
5
8
3
9.5–91.5°C; [h] =−19.4 (c 0.51, CCl ); IR (KBr):
D 4
1
355.3 s, 1572.1 s, 1559.8 s; H NMR (300 MHz,
3
.4. General procedure for copper-catalyzed allylic oxi-
CDCl ): 1.27 (s, 3H), 1.31 (s, 3H), 1.20–1.40 (m, 1H),
3
dation Cu(I) complexes of ligands 1–8 as catalyst
1.90–2.30 (m, 6H), 2.60–2.75 (m, 1H), 4.75 (s, 1H), 7.32
(
m, 1H), 7.50, (d, 1H, J=7.7 Hz), 7.70–7.90 (m, 2H),
The copper catalyst was generated by stirring 1–8 (0.06
8
1
2
1
1
2
.30 (d, 1H, J=7 Hz), 8.41 (d, 1H, J=7.7 Hz), 8.67 (d,
1
3
mmol) with copper(I) salt (0.05 mmol) in CH CN (3
3
H, J=4.4 Hz); C NMR (75 MHz, CDCl ): 23.52,
3
mL) under nitrogen. Alkene (4 mmol) was added, fol-
lowed by the slow addition of tert-butyl perbenzoate (1
mmol, 190 mL) over a 1 min period. The reaction was
monitored by GLC and was quenched by adding a
5.06, 27.78, 29.90, 38.92, 40.11, 53.55, 78.85, 118.91,
19.74, 120.80, 123.56, 136.62, 137.30, 148.86, 153.83,
+
55.51, 165.63; MS (EI) m/z (rel. int.): 294 (M , 21),
11 (69), 183 (51), 170 (43), 155 (base). Anal. calcd for
saturated solution of NaHCO . The mixture was
3
C H N O: C, 77.52; H, 7.53; N, 9.52. Found: C,
1
9
22
2
extracted with diethyl ether and evaporated. The
product was purified by column chromatography
7
7.67; H, 7.84; N, 9.27%.
(
petroleum ether/EtOAc) and was then characterized by
H NMR, C NMR, IR, and GC–MS. The enan-
3
.3. General procedure for the synthesis of pyridyl
1
13
alcohols 13 and 14
tiomeric excess of the product was determined by
HPLC with a Daicel Chiralcel OD or OJ column, using
hexane/propan-2-ol=1000/1 as the eluent.
A solution of bromopyridyl alcohol 9 or 10 (5.76
mmol) and tetrakis(triphenylphosphine)palladium(0)
(
0.17 mmol, 0.2 g) in toluene (12 mL) was treated with
a solution of Na CO (11.53 mmol, 1.22 g) in H O (6
2
3
2
mL), followed by a solution of phenylboronic acid (6.92
mmol, 0.84 g) in MeOH (3 mL). The mixture was
Acknowledgements
stirred at 85°C for 4 h under N . After cooling to rt, a
2
solution of concentrated aqueous NH3 (2.9 mL) in
saturated aqueous Na CO (29 mL) was added and the
Financial support for this research from the Hong
Kong Research Grants Council (CERG Grant No.
2
3
mixture was extracted with CH Cl (3×50 mL). The
2
2
9
040543) and the City University of Hong Kong (SRG
Grant No. 7001062) is gratefully acknowledged.
combined organic layers were washed with brine (50
mL), dried over Na SO and filtered. Evaporation of
2
4
the filtrate under reduced pressure gave crude product,
which was purified by chromatography (25:1 petroleum
ether–ethyl acetate). The product was characterized by
References
1
13
IR, H NMR, C NMR, MS and CHN.
1
. Kharasch, M. S.; Fono, A. J. Org. Chem. 1958, 23, 324.
3
.3.1. Pyridyl alcohol 13. Following the above proce-
2. Kochi, J. K. J. Am. Chem. Soc. 1961, 83, 3162.
3. Beckwith, A. L. J.; Evans, G. W. Proc. Chem. Soc. 1962,
63.
dure, using bromopyridyl alcohol 9 and usual work-up
2
5
gave 0.78 g (44%) of 13: mp 107–109°C; [h] =−71.2 (c
D
1
0
.51, CCl ); IR (KBr): 3359.8 s, 1570.1 s; H NMR
4. Denney, D. Z.; Appelbaum, A.; Denney, D. B. J. Am.
4
(CDCl ): l 0.49 (s, 3H), 1.03 (s, 3H), 1.04 (s, 3H), 1.17
Chem. Soc. 1962, 84, 4969.
3
(
2
m, 1H), 1.38 (d, 2H, J=10 Hz), 1.51 (m, 1H), 1.84 (m,
H), 2.38 (m, 2H), 6.25 (s, 1H), 7.35–7.50 (m, 4H), 7.59
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2084.
(
d, 1H, J=7.7 Hz), 7.70 (t, 1H, J=7.7 Hz), 7.99 (d, 2H,
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1
3
J=7.7 Hz); C NMR (CDCl ): l 17.21, 22.31, 24.40,
3
2
1
1
2
9.29, 32.49, 41.94, 45.95, 48.78, 51.81, 83.66, 117.71,
21.36, 126.48, 128.46, 128.79, 136.79, 138.51, 153.79,
8. Denney, D. B.; Napier, R.; Cammarata, A. J. Org. Chem.
+
61.72; MS (EI) m/z (rel. int.): 307 (M , 6), 279 (28),
1965, 30, 3151.
26 (74), 210 (base), 169 (31), 154 (99). Anal. calcd for
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C H NO: C, 82.35; H, 7.84; N, 4.58. Found: C, 82.05;
2
1
24
H, 7.88; N, 4.33%.

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