Aluminosilicate catalysis of chalcone Diels-Alder reactions

Article abstract of DOI:10.1080/00397910701796527

Previously unreported Diels-Alder adducts of substituted chalcones with isoprene and myrcene have been formed at more than 0°C by employing a nanoporous aluminosilicate catalyst. This catalyst eliminates problems with diene polymerization that are encountered with many other Lewis acids. The chalcone component has some size restrictions. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397910701796527

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Aluminosilicate Catalysis of Chalcone
Diels–Alder Reactions
a
a
Jennifer L. Corbett & Rex T. Weavers
a
Department of Chemistry , University of Otago , Dunedin, New Zealand
Published online: 27 Feb 2008.
To cite this article: Jennifer L. Corbett & Rex T. Weavers (2008) Aluminosilicate Catalysis of Chalcone
Diels–Alder Reactions, Synthetic Communications: An International Journal for Rapid Communication of
Synthetic Organic Chemistry, 38:4, 489-498, DOI: 10.1080/00397910701796527
To link to this article: http://dx.doi.org/10.1080/00397910701796527
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Synthetic Communications , 38: 489–498, 2008
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910701796527
Aluminosilicate Catalysis of Chalcone
Diels–Alder Reactions
Jennifer L. Corbett and Rex T. Weavers
Department of Chemistry, University of Otago, Dunedin, New Zealand
Abstract: Previously unreported Diels–Alder adducts of substituted chalcones with
isoprene and myrcene have been formed at less than 08C by employing a nanoporous
aluminosilicate catalyst. This catalyst eliminates problems with diene polymerization
that are encountered with many other Lewis acids. The chalcone component has
some size restrictions.
Keywords: aluminosilicate catalyst, chalcone, Diels–Alder, isoprene, myrcene
Panduratin A (1), a natural anti-inflammatory compound isolated from
Boesenbergia pandurata (finger root ginger),
[1]
is regarded as being
formally derived from a Diels–Alder reaction between a chalcone and the
monoterpene, ocimene. Our interest was to synthesize analogs of 1 for
assessment as potential anti-inflammatories. Literature reports of uncatalyzed
Diels–Alder reactions of chalcones are relatively few in number, and those
[
2]
that have been successful have required forcing conditions.
Received in the USA August 21, 2007
Address correspondence to Rex T. Weavers, Department of Chemistry, University
of Otago, Box 56, Dunedin 9054, New Zealand. E-mail: rweavers@chemistry.otago.
ac.nz
4
89

4
90
J. L. Corbett and R. T. Weavers
Trial studies were conducted, employing isoprene (2) as the diene and
either cinnamaldehyde or chalcone (3a) as the dienophile. In both cases,
heating the two compounds for an extended period at 808C in the absence
of solvent resulted in no reaction. Use of the Lewis acid catalysts FeCl on
3
.
silica, BF3 Et O, or EtAlCl resulted in extensive polymerization of the
isoprene with no significant adduct formation.
2
2
An aluminium hexagonal molecular silica (Al-HMS), prepared by reaction
of tetraethyl orthosilicate and aluminium isopropoxide in the presence of hexa-
decylamine, has been reported to catalyze the Diels–Alder reaction between
[
3]
isoprene and methyl acrylate. Reaction proceeded at 218C to give a 95%
yield of the adduct. We have now employed this catalyst to prepare some new
adducts of isoprene and myrcene with various substituted chalcones
(
Scheme 1, Table 1).
Reaction of chalcone 3a with 2 at 218C and at room temperature gave
similar yields, but the NMR spectrum of the crude mixture at the higher
temperature showed a small but significant increase in the levels of minor
by-products. These NMR spectra revealed that the product was almost
entirely one regioisomer.
Further NMR spectral studies revealed the orientation of the
cycloaddition; in particular the homonuclear correlation spectroscopy
(
(
COSY) and heteronuclear multiple bond correlation (HMBC) experiments
Fig. 1). The COSY spectrum of the purified product showed the separation
1
00
00
of the phenyl H NMR resonances into a deshielded (H-2 -H-6 ) and a
000
000
shielded set (H2 -H-6 ). Heteronuclear single-quantum coherence (HSQC)
and HMBC correlations to these allowed assignment of all phenyl carbon
0
00
000
signals. The HMBC spectrum linked H-2 /6 (d 7.20) to a methine carbon
0
signal (d 42.8) that could be assigned to C-2 . Correlation was also
0
000
000
observed between H-2 (d 3.33) and C-2 /6 (d 127.5). A COSY correlation
0
0
to H-2 established the H-1 signal (d 3.93). The two allylic methylene groups
C-3 and C-6 ) could be distinguished by a COSY correlation between the
0 0
(
olefinic
0
0
proton,
d 2.31, 2.36), along with the facts that the H-6 peaks were broader than
H-5
(d
5.50),
and
0
the
H-6
signals
(
Scheme 1. Diels–Alder reactions of chalcones.

Chalcone Diels–Alder Reactions
491
Table 1. Reaction of isoprene (2) with chalcones at 218C catalyzed by Al-HMS
Product
(% yield)
Diene
Dienophile
X ¼
Time (h)
2
2
2
2
2
2
2
5
5
5
5
5
5
5
3a
3b
3c
3d
3e
3f
H
o-OCH
46
70
94
69
75
75
73
70
70
47
69
74
75
73
4a (61)
4b (76)
4c (43)
3
m-OCH3
p-OCH3
No reaction
4e (28)
4f (78)
p-CH
p-F
3
3g
3a
3b
3c
3d
3e
3f
o-OH
H
o-OCH
No reaction
6a (73)
6b (76)
3
m-OCH3
p-OCH
6c (23)
3
No reaction
No reaction
6f (78)
p-CH
p-F
3
3g
o-OH
No reaction
0
those of H-3 and there was an HMBC correlation from the methyl proton
0
resonance (d 1.74) to the C-3 carbon signal (d 39.0). COSY correlations
0
0
0
0
linked H-3 to H-2 and H-6 to H-1 establishing 3a as the regioisomer that
0
0
had been formed. HMBC correlation between H-5 and C-1 (d 46.6) gave
1
further support for this conclusion. The H NMR coupling constants
0
0
measured for H-1 (J ¼ 5.5, 10, 11 Hz) and H-2 (J ¼ 7, 10, 10 Hz) were con-
0
0
sistent with a diaxial relationship between H-1 and H-2 , in accordance with
the anticipated trans stereochemistry.
Reaction with isoprene was attempted with a variety of substituted
chalcones (Scheme 1, Table 1). Successful synthesis of adducts was
achieved with o- and m-methoxychalcone, but the p-isomer did not react
either at 218C or at room temperature. However, the p-methyl and fluoro
derivatives did produce Diels–Alder adducts. o-Hydroxy chalcone also
yielded no adduct.
Figure 1. Key COSY and HMBC correlations in 3b.

4
92
J. L. Corbett and R. T. Weavers
The fact that the o- and m-methoxy chalcones reacted but the p-isomer did
not suggested that the controlling feature was a size factor rather than an elec-
tronic one. Molecular modeling was carried out in an effort to establish struc-
tural limits for a successful reaction. Conformational searching on chalcone 3a
2
1
yielded five low-energy conformations within a 2 kJ mol energy window.
These forms had either transoid or cisoid conformations of the enone
system. Analysis of the other chalcones yielded similar sets of structures.
The lowest-energy conformation for chalcone 3a had a transoid geometry,
and for size comparison, the conformation matching was used for each of
the substituted chalcones, even in cases (3b, 3d, and 3g) where this was not
the lowest-energy form. In each case, examination of the constructed
surface for the lowest-energy conformation revealed that all the reactants
used, with the exception of the unreactive p-methoxychalcone, extended no
˚
further than 7.5A from the center of the reacting double bond. This gives
some indication of the size of the catalytic site. The lack of reactivity of
o-hydroxychalcone, which does not have an apparent size constraint,
implies that strong polar interactions may interfere with appropriate orien-
tation of the dienophile within the catalyst.
The catalyst proved to be capable of accommodating a larger diene.
Reaction of the same set of dienophiles with myrcene (5) also yielded some
adducts (Scheme 1, Table 1).
Quite good yields were obtained in three cases, but with a larger diene
there appeared to be a little less tolerance for a larger dienophile, as p-methyl-
chalcone did not react under the conditions used.
This catalyst system provides simple access to some otherwise
inaccessible Diels–Alder adducts. NMR studies reveal that the regioselectiv-
ity is the same in all cases. Similar catalyst systems with larger pore size may
allow successful reaction with bulkier substituted chalcones.
EXPERIMENTAL
With the exception of 3g, which was synthesized using the method outlined in
Ref. [4], the substituted chalcones were synthesized from the corresponding
[
5]
substituted acetophenone and benzaldehyde using NaOH in dioxane.
aq
1
Compounds 3b–3g were characterized by comparison of H, C, and
13
19
F
[6]
(
compound 3f) NMR spectra with published data. Melting points were
obtained on a Mettler Toledo FP62 instrument calibrated with benzoic acid
mp 122.48C). IR spectra were recorded on a Perkin-Elmer Spectrum BX
FTIR system as KBr disks or as neat films. NMR spectra were recorded at
(
1
13
5
at 282 MHz ( F) on a Varian Inova-300 spectrometer. Spectra were
00 MHz ( H) and 125 MHz ( C) on a Varian Inova-500 spectrometer or
1
9
1
recorded in CDCl and are referenced to residual CHCl for H (d 7.26),
3
3
1
CDCl for C (d 77.1), and external CF COOH for F (d 77.0). High-resol-
3
19
3
3
ution electrospray mass spectra were recorded on a Bruker Daltonics

Chalcone Diels–Alder Reactions
493
MicroTOF spectrometer. Microanalyses were performed by the Campbell
Microanalytical Laboratory, University of Otago. Molecular mechanics con-
formational searches were performed with the aid of PCModel version 9
using the MMX forcefield with the mixed Monte Carlo coordinate
[7]
movements/bond rotations strategy for the generation of initial structures.
The default cutoff criteria were employed. Molecular surfaces and distances
[8]
were calculated using the UCSF Chimera package.
Aluminum Hexagonal Molecular Silica (Al-HMS)
A homogenous solution of tetraethyl orthosilicate (10.6 g, 51.1 mmol) and
aluminum isopropoxide (1.45 g, 7110 mmol) was added to a vigorously
stirred solution of hexadecylamine (3.53 g, 14.6 mmol) in ethanol (45.0 ml,
766 mmol) and deionized water (23.3 g, 1290 mmol) at room temperature.
The mixture was vigorously stirred for 96 h. The white gel was collected by
filtration, dried at room temperature under an N flow, and then calcined in
2
dry air in an electric furnace at 5008C for 5 h.
General Procedure for Al-HMS-Catalyzed Diels–Alder Reaction
Al-HMS was predried for 2 h at 4008C/0.5 mm prior to reaction. Al-HMS
(0.304 g) was added to a mixture of dienophile (1.0 mmol) and diene
(3.0 mmol) in dry petroleum ether (6.00 mL) at room temperature. The
mixture was then stirred vigorously at 218C for the designated time.
The catalyst was removed by filtration, and the solvent was evaporated. The
crude material was chromatographed on silica gel, eluting with a dichloro-
methane/petroleum ether gradient. Reactions are reported according to this
convention: dienophile (mass, amount), diene, reaction time, product (mass,
percent yield).
Data
(4-Methyl-6-phenylcyclohex-3-enyl)(phenyl)methanone (4a)
Compound 3a (0.224 g, 1.08 mmol), 2, 46 h, 4a (off-white crystals, 0.182 g,
2
1
6
3
1
1%). Recrystallized petroleum ether. Mp ¼ 101.08C. IR nmax (KBr)/cm
058, 3001, 2976, 2925, 2896, 2827, 1672, 1592, 1578, 1497, 1447, 1380,
1
280, 1235, 1200, 1180, 1002, 863, 773, 751, 703, 539. H NMR d 1.74
0000 0 0
(
3H, br. s, H-1 ), 2.29 (2H, m, H-3 ), 2.31 (1H, m, H-6 ), 2.36 (1H, m,
0
0
H-6 ), 3.33 (1H, ddd, J ¼ 10, 10, 7 Hz, H-2 ), 3.93 (1H, ddd, J ¼11, 10,
0
0
000
5
.5 Hz, H-1 ), 5.50 (1H, br. s, H-5 ), 7.05 (1H, tt, J ¼ 7, 1.5 Hz, H-4 ),
000 000
7
.16 (2H, ddm, J ¼ 8, 8 Hz, H-3 , 5 ), 7.20 (2H, dd, J ¼ 7, 1.5 Hz,

4
94
J. L. Corbett and R. T. Weavers
0
00
000
00
00
00
H-2 , 6 ), 7.36 (2H, ddm, J ¼ 8, 8 Hz, H-3 , 5 ), 7.47 (1H, dd, J ¼ 7.5,
00
00
13
1
.5 Hz, H-4 ), 7.80 (2H, dd, J ¼ 8, 1.5 Hz, H-2 , 6 ). C NMR d 23.2
0000 0 0 0 0 0
(
C-1 ), 30.9 (C-6 ), 39.0 (C-3 ), 42.8 (C-2 ), 46.6 (C-1 ), 119.3 (C-5 ),
000 000 000 00 00 000 000
1
26.2 (C-4 ), 127.5 (C-2 , 6 ), 128.0 (C-2 , 6 ), 128.4 (C-3 , 5 ), 128.5
00 00 00 0 00 000
(
C-3 , 5 ), 132.8 (C-4 ), 134.1 (C-4 ), 137.4 (C-1 ), 144.7 (C-1 ),
203.7 (C-1). Anal. calcd. for C H O: C, 86.92; H, 7.29. Found: C,
20 20
86.83; H, 7.04.
(
2-Methoxyphenyl)(4-methyl-6-phenylcyclohex-3-enyl)methanone (4b)
Compound 3b (0.249 g, 1.04 mmol), 2, 70 h, 4b (pale yellow crystals, 0.243 g,
2
1
7
3
1
6%). Recrystallized petroleum ether. Mp ¼ 838C. IR n
(KBr)/cm
max
060, 3043, 3015, 2955, 2929, 2889, 2840, 1670, 1600, 1578, 1483, 1436,
0
1
0000
400. H NMR d 1.71 (3H, br. s, H-1 ), 2.21 (2H, d, J ¼ 8 Hz, H-3 ), 2.36
0
0
(
1H, m, H-6 ), 2.41 (1H, dm, J ¼ 17 Hz, H-6 ), 3.19 (1H, ddd, J ¼ 11, 8,
0
0
00
8
Hz, H-2 ), 3.79 (1H, ddd, J ¼ 11, 11, 5 Hz, H-1 ), 3.85 (3H, s, H-2 -
0
0
0
OMe), 5.51 (1H, br. s, H-5 ), 6.73 (1H, ddd, J ¼ 7.5, 7.5, 1 Hz, H-5 ), 6.81
00
00
(
1H, dd, J ¼ 7.5, 1.5 Hz, H-6 ), 6.84 (1H, d, J ¼ 8 Hz, H-3 ), 7.08 (1H, m,
000 000 000
H-4 ), 7.13 (2H, dd, J ¼ 7.5, 7.5 Hz, H-3 , 5 ), 7.14 (2H, dd, J ¼ 7.5,
000
000
00
13
1
.5 Hz, H-2 , 6 ), 7.29 (1H, td, J ¼ 7.5, 1.5 Hz, H-4 ). C NMR 23.3
0000 0 0 0 0 00
(
C-1 ), 29.3 (C-6 ), 38.6 (C-3 ), 43.7 (C-2 ), 51.8 (C-1 ), 55.5 (C-2 -OMe),
00 0 00 000 000 000
1
1
1
8
10.9 (C-3 ), 120.0 (C-5 ), 120.5 (C-5 ), 126.1 (C-4 ), 127.9 (C-2 , 6 ),
28.1 (C-3 , 5 ), 129.4 (C-6 ), 130.8 (C-1 ), 132.3 (C-4 ), 133.4 (C-4 ),
0
0
00
00
000
00
00
00
0
00
44.6 (C-1 ), 157.4 (C-2 ), 207.9 (C-1). Anal. calcd. for C H O : C,
1 22 2
2
2.32; H, 7.24. Found: C, 82.23; H, 7.39.
(
3-Methoxyphenyl)(4-methyl-6-phenylcyclohex-3-enyl)methanone (4c)
Compound 3c (0.138 g, 0.58 mmol), 2, 94 h, 4c (colorless oil, 0.077 g, 43%).
2
1
1
IR nmax (KBr)/cm 3424, 2926, 1677, 1596, 1488, 1453, 1430, 1259. H
0000
0
NMR d 1.74 (3H, br. s, H-1 ), 2.28 (2H, br. d, J ¼ 6 Hz, H-3 ), 2.31 (1H,
0
0
m, H-6 ), 2.40 (1H, dm, J ¼ 16.5 Hz, H-6 ), 3.33 (1H, ddd, J ¼ 11, 10,
0
00
6
.5 Hz, H-2 ), 3.78 (3H, s, H-3 -OMe), 3.90 (1H, ddd, J ¼ 11, 10, 5.5 Hz,
0
0
0
0
H-1 ), 5.50 (1H, br. s, H-5 ), 7.03 (1H, dd, J ¼ 8, 1 Hz, H-4 ), 7.07 (2H, tt,
000
000
00
000
J ¼ 7, 1.5 Hz, H-4 ), 7.17 (1H, ddm, J ¼ 7.5, 7.5 Hz, H-3 , 5 ), 7.20 (2H,
000
000
dd, J ¼ 8, 1.5 Hz, H-2 , 6 ), 7.29 (1H, d, J ¼ 1.5 Hz, H-2 ), 7.29 (1H, dd,
00
00 13
J ¼ 8, 8 Hz, H-5 ), 7.44 (1H, br. ddd, I ¼ 7.5, 1.5, 1.5 Hz, H-6 ). C NMR
0000
0
0
0
0
00
000
d 23.2 (C-1 ), 31.0 (C-6 ), 39.0 (C-3 ), 42.8 (C-2 ), 46.8 (C-1 ), 55.4 (C-3 -
OMe), 112.3 (C-2 ), 119.3 (C-5 ), 119.4 (C-4 ), 120.6 (C-6 ), 126.2 (C-4 ),
00
0
00
00
000 000 000 000 00 0
1
1
27.5 (C-2 , 6 ), 128.4 (C-3 , 5 ), 129.4 (C-5 ), 134.1 (C-4 ), 138.8 (C-
), 144.7 (C-1 ), 159.8 (C-3 ), 203.5 (C-1). HRMS calcd. C H NaO
2
00
000
00
2
1
22
þ
[
M þ Na] 329.1512; found 329.1516.

Chalcone Diels–Alder Reactions
4-Methylphenyl)(4-methyl-6-phenylcyclohex-3-enyl)methanone (4e)
Compound 3e (0.223 g, 1.00 mmol), 2, 75 h, 4e (colorless oil. 0.081 g, 28%).
495
(
2
1
IR n
1
(film)/cm 3060, 3028, 2912, 1673, 1606, 1453, 1408, 1285, 1233,
max
1
0000
0
180. H NMR d 1.74 (3H, br. s, H-1 ), 2.28 (1H, br. d, J ¼ 6 Hz, H-3 ), 2.31
0
0
0
(
1H, m, H-6 ), 2.35 (3H, s, H-4 -Me), 2.35 (1H, m, H-), 3.33 (1H, ddd, J ¼ 10,
0
0
1
0, 6.5 Hz, H-2 ), 3.92 (1H, ddd, J ¼ 11, 10, 5.5 Hz, H-1 ), 5.51 (1H, br.s,
0 000 000
H-5 ), 7.06 (1H, tt, J ¼ 7, 1.5 Hz, H-4 ), 7.16 (2H, dd, J ¼ 8, 8 Hz, H-3 ,
0
0
0
00
00
000
00
00
000
5
6
1
), 7.16 (2H, d, J ¼ 7.5 Hz, H-3 , 5 ), 7.20 (2H, dd, J ¼ 8, 1.5 Hz, H-2 ,
0
0
00 13
0
0
), 7.73 (2H, d, J ¼ 8 Hz, H-2 , 6 ). C NMR d 21.6 (C-4 -Me), 23.2 (C-
0
0
0
0
0
), 31.0 (C-6 ), 39.0 (C-3 ), 42.7 (C-2 ), 46.3 (C-1 ), 119.4 (C-5 ), 126.2
000 000 000 00 00 000 000 00
(
C-4 ), 127.4 (C-2 , 6 ), 128.2 (C-2 , 6 ), 128.4 (C-3 , 5 ), 129.2 (C-3 ,
), 134.1 (C-4 ), 134.8 (C-1 ), 143.5 (C-4 ), 144.9 (C-1 ), 203.2 (C-1).
00
0
00
þ
00
000
5
HRMS calcd. C H NaO [M þ Na] 313.1563; found 313.1563.
2
1
22
1
(4-Fluorophenyl)(4-methyl-6-phenylcyclohex-3-enyl)methanone (4f)
Compound 3f (0.237 g, 1.05 mmol), 2, 75 h, 4f (pale yellow oil. 0.269 g,
2
1
7
1
8%). IR nmax (KBr)/cm
3064, 3028, 2929, 1681, 1598, 1506, 1453,
1
266, 1231, 1157. H NMR d 1.74 (3H, s, H-s), 2.29 (1H, dm, J ¼ 9.5 Hz,
H-s), 2.34 (1H, m, H-s), 2.36 (1H, m, H-), 3.30 (1H, ddd, J ¼ 11, 9, 7.5 Hz,
H-s), 3.87 (1H, ddd, J ¼ 11, 10, 6 Hz, H-s), 5.50 (1H, br. s, H-s), 7.02 (2H,
dd, J ¼ 8,8.5 Hz, H-d), 7.06 (1H, m, H-s), 7.15 (2H, ddm, J ¼ 8, 8 Hz,
H-s), 7.16 (2H, dm, J ¼ 8 Hz, H-s), 7.81 (2H, dd, J ¼ 5.5, 8.5 Hz, H-d).
1
3
0000
0
0
0
0
000
C NMR d 23.2 (C-1 ), 30.8 (C-6 ), 38.9 (C-3 ), 43.0 (C-2 ), 46.6 (C-1 ),
0
0
00
0
000
1
15.5 (d, J ¼ 22 Hz, C-3 , 5 ), 119.2 (C-5 ), 126.3 (C-4 ), 127.5 (C-2 ,
000 000 000 00 00
6
), 128.4 (C-3 , 5 ), 130.6 (d, J ¼ 9.5 Hz, C-2 , 6 ), 133.8
00
0
000
(
d, J ¼ 2.5 Hz, C-1 ), 134.1 (C-4 ), 144.5 (C-1 ), 165.6 (d, J ¼ 254 Hz,
00
19
C-4 ), 202.2 (C-1). F NMR d 106.3, tt, J ¼ 5.5,8.5 Hz. HRMS calcd.
þ
C H FNaO [M þ Na] 317.1312; found 317.1312.
2
0
19
1
(4-(4-Methylpent-3-enyl)-6-phenylcyclohex-3-enyl)(phenyl)methanone (6a)
Compound 3a (0.273 g, 1.30 mmol), 5, 70 h, 6a (white crystals. 0.331 g,
1
2
7
3%). Recrystallized petroleum ether. Mp ¼ 80.68C. IR n
(KBr)/cm
max
1
969, 2907, 2833, 1666, 1448, 1234, 1198, 756, 701. H NMR d 1.62 (3H,
2
0000
0000
0000
br. s, H-4 -Me), 1.70 (3H, br. d, J ¼ 1 Hz, H-5 ), 2.12 (2H, m, H-2 ),
0
0
2
.30 (2H, m, H-3 ), 2.34 (1H, m, H-6 ), 2.41 (1H, br. ddd, J ¼ 17, 5, 5 Hz,
0
0
H-6 ), 3.31 (1H, ddd, J ¼ 10.5, 10.5, 6 Hz, H-2 ), 3.94 (1H, ddd, J ¼ 10.5,
0
0000
0
1
7
5
0.5, 5 Hz, H-1 ), 5.13 (1H, tm, J ¼ 7 Hz, H-3 ), 5.52 (1H, br. s, H-5 ),
0
0
0
0
0
0
.06 (1H, tt, J ¼ 7, 1.5 Hz, H-4 ), 7.16 (2H, ddm, J ¼ 7.5, 7.5 Hz, H-3 ,
000
000
000
), 7.19 (2H, dm, J ¼ 7.5 Hz, H-2 , 6 ), 7.37 (2H, ddm, J ¼ 8, 8 Hz,
0
0
00
00
H-3 , 5 ), 7.48 (1H, tt, J ¼ 7.5, 1 Hz, H-4 ), 7.81 (2H, dd, J ¼ 8.5, 1 Hz,
00
00 13
0000
0000
0000
H-2 , 6 ). C NMR d 17.8 (C-4 -Me), 25.8 (C-5 ), 26.5 (C-2 ), 30.9
(C-6 ), 37.4 (C-1 ), 37.4 (C-3 ), 42.9 (C-2 ), 46.8 (C-1 ), 118.9 (C-5 ),
0 0000 0 0 0 0

4
96
J. L. Corbett and R. T. Weavers
0000 000 000 000 00 00 00
24.1 (C-3 ), 126.2 (C-4 ), 127.5 (C-2 , 6 ), 128.1 (C-3 , 5 ), 128.4 (C-2 ,
1
00
000 000 0000 00 00 0
6 ), 128.5 (C-3 , 5 ), 131.7 (C-4 ), 132.8 (C-4 ), 137.4 (C-1 ), 137.8 (C-4 ),
000
44.8 (C-1 ), 203.7 (C-1). Anal. calcd. for C H O: C, 87.16; H, 8.19.
25 28
1
Found: C, 87.06; H, 8.37.
(
2-Methoxyphenyl)(4-(4-methylpent-3-enyl)-phenylcyclohex-
-enyl)methanone (6b)
3
Compound 3b (0. 225 g, 0.94 mmol), 5, 70 h, 6b (yellow oil. 0.117 g, 33%).
IR n
21
(film)/cm 2955, 2930, 2887, 1670, 1598, 1455, 1377, 1245, 1163,
max
1
0000
0000
9
11. H NMR d 1.62 (3H, br. s, H-4 -Me), 1.70 (3H, br. d, J ¼ 1 Hz, H-5 ),
0000 0000
2
.02 (2H, br. t, J ¼ 8 Hz, H-1 ), 2.11 (2H, br dt, J ¼ 8, 8 Hz, H-2 ), 2.23
0
0
(
2H, m, H-3 ), 2.47 (, ddd, J ¼ 17.5, 5, 5 Hz, H-6 ), 3.18 (1H, ddd, J ¼ 11,
0
0
1
0, 6.5 Hz, H-2 ), 3.80 (1H, ddd, J ¼ 11, 10, 5.5 Hz, H-1 ), 3.85 (3H, s,
00 0000 0
H-2 -OMe), 5.12 (1H, tm, J ¼ 7 Hz, H-3 ), 5.53 (1H, br. s, H-5 ), 6.73
0
0
00
000
(
1H, ddd, J ¼ 7.5, 7.5, 1 Hz, H-5 ), 6.80 (1H, dd, J ¼ 7.5, 2 Hz, H-6 ),
00
000
6
.84 (1H, br. d, J ¼ 8 Hz, H-3 ), 7.08 (1H, m, H-4 ), 7.13 (2H, m, H-3 ,
000 000 000 00
5
), 7.14 (2H, m, H-2 , 6 ), 7.30 (1H, ddd, J ¼ 8.5, 7.5, 1.5 Hz, H-4 ).
1
3
0000
0000
0000
0
C NMR d 17.8 (C-4 -Me), 25.8 (C-5 ), 26.5 (C-2 ), 29.4 (C-6 ), 37.0
0 0000 0 0 00
(
C-3 ), 37.4 (C-1 ), 43.8 (C-2 ), 51.9 (C-1 ), 55.5 (C-2 -OMe), 110.9 (C-
0
0
0
0
00
0
0 00 0000 000 000
), 119.6 (C-5 ), 120.5 (C-5 ), 124.3 (C-3 ), 126.1 (C-4 ), 127.9 (C-2 ,
3
6
4
000
000
00
00
0000
), 128.1 (C-3 , 5 ), 129.4 (C-6 ), 130.8 (C-1 ), 131.6 (C-4 ), 132.2 (C-
000
0
þ
00
), 137.1 (C-4 ), 144.7 (C-1 ), 157.4 (C-2 ), 208.0 (C-1). HRMS calcd.
C H NaO [M þ Na] 397.2138; found 397.2130.
2
6
30
2
(
3-Methoxyphenyl)(4-(4-methylpent-3-enyl)-phenylcyclohex-
-enyl)methanone (6c)
3
Compound 3c (0. 307 g, 1.29 mmol), 5, 70 h, 6c (colorless oil. 0.111 g, 23%).
IR n
2
1
(film)/cm 3417, 3028, 2926, 1720, 1677, 1596, 1582, 1452, 1430,
max
1
0000
1
258. H NMR d 1.61 (3H, br. s, H-4 -Me), 1.69 (3H, br. d, J ¼ 1 Hz,
0
0
000
000
0000
H-5 ), 2.02 (2H, br. t, J ¼ 7 Hz, H-1 ), 2.12 (2H, br. dt, J ¼ 7, 7 Hz,
0
0
H-2 ), 2.30 (2H, m, H-3 ), 2.43 (1H, dm, J ¼ 17 Hz, H-6 ), 3.30 (1H, ddd,
0
00
J ¼ 11, 11, 6 Hz, H-2 ), 3.78 (3H, s, H-3 -OMe), 3.91 (1H, ddd, J ¼ 11, 11,
0
0000
5
.5 Hz, H-1 ), 5.12 (1H, tm, J ¼ 7 Hz, H-3 ), 5.51 (1H, br. d, J ¼ 5 Hz,
0
0
0
0
0
0
H-5 ), 7.03 (1H, ddd, J ¼ 8, 2.5, 1 Hz, H-4 ), 7.07 (1H, tt, J ¼ 7, 1, H-4 ),
000
000
7
.17 (2H, br. dd, J ¼ 7, 7 Hz, H-3 , 5 ), 7.19 (2H, dd, J ¼ 7.5, 1.5 Hz,
000 000 00
H-2 , 6 ), 7.28 (1H, d, J ¼ 2 Hz, H-2 ), 7.29 (1H, dd, J ¼ 7.5, 7.5 Hz,
0
0
00 13
0000
H-5 ), 7.44 (1H, d, J ¼ 7.5 Hz, H-6 ). C NMR d 17.8 (C-4 -Me), 25.8 (C-
0
000
0000 0 0000 0 0
5
), 26.5 (C-2 ), 31.0 (C-6 ), 37.4 (C-1 ), 37.5 (C-3 ), 42.9 (C-2 ), 47.0 (C-
), 55.4 (C-3 -OMe), 112.3 (C-2 ), 118.9 (C-5 ), 119.4 (C-4 ), 120.7 (C-6 ),
0
00 00 0 00 00
1
1
0000
000
000
000
00
000
000
000
24.1 (C-3 ), 126.2 (C-4 ), 127.5 (C-2 , 6 ), 128.4 (C-3 , 5 ), 129.4 (C-
00
0
0
0000
0
5
2
), 131.7 (C-4 ), 137.8 (C-4 ), 138.8 (C-1 ), 144.8 (C-1 ), 159.8 (C-3 ),
þ
03.5 (C-1). HRMS calcd. C H NaO [M þ Na] 397.2138; found 397.2153.
2
6
30
2

Chalcone Diels–Alder Reactions
497
(
4-Fluorophenyl)(4-(4-methylpent-3-enyl)-phenylcyclohex-
-enyl)methanone (6f)
3
Compound 3f (0. 237 g, 1.05 mmol), 5, 75 h, 6f (colorless oil. 0.269 g, 78%).
2
1
IR n
1
(film)/cm
3422, 3028, 2925, 1678, 1597, 1376, 1230, 1156.
0000
max
0000
H NMR d 1.62 (3H, br. s, H-4 -Me), 1.70 (3H, br. d, J ¼ 1 Hz, H-5 ),
0
000
0000
2
.05 (2H, br. t, J ¼ 7.5 Hz, H-1 ), 2.12 (2H, m, H-2 ), 2.31 (2H, br. d,
0
0
0
J ¼ 6 Hz, H-3 ), 2.36 (1H, m, H-6 ), 2.38 (1H, m, H-6 ), 3.28 (1H, ddd,
0
0
J ¼ 10, 10, 6.5 Hz, H-2 ), 3.88 (1H, ddd, J ¼ 10, 10, 5.5 Hz, H-1 ), 5.13
0
000
0
(
1H, tm, J ¼ 7 Hz, H-3 ), 5.52 (1H, br. s, H-5 ), 7.02 (2H, dd, J ¼ 8.5,
00
00
000
8
.5 Hz, H-3 , 5 ), 7.06 (1H, br. tt, J ¼ 7, 2 Hz, H-4 ), 7.16 (2H, dd,
000 000 000 000
J ¼ 7.5, 7.5 Hz, H-3 , 5 ), 7.19 (2H, dd, J ¼ 7.5, 2 Hz, H-2 , 6 ), 7.82
0
0
00 13
0000
(
2H, dd, J ¼ 8.5, 5.5 Hz, H-2 , 6 ). C NMR d 17.8 (C-4 -Me), 25.8 (C-
0
000
0000 0 0000 0 0
5
), 26.5 (C-2 ), 30.9 (C-6 ), 37.3 (C-1 ), 37.4 (C-3 ), 43.0 (C-2 ), 46.8
0
00
00
0
0000
(
C-1 ), 115.5 (d, J ¼ 22 Hz, C-3 , 5 ), 118.8 (C-5 ), 124.1 (C-3 ), 126.3
000 000 000 000 000 00 00
(
C-4 ), 127.5 (C-2 , 6 ), 128.4 (C-3 , 5 ), 130.6 (d, J ¼ 9 Hz, C-2 , 6 ),
0
000
00
19
0
000
1
1
8
7
31.8 (C-4 ), 133.8 (d, J ¼ 2.5 Hz, C-1 ), 137.9 (C-4 ), 144.6 (C-1 ),
00
65.5 (d, J ¼ 254 Hz, C-4 ), 202.2 (C-1). F NMR d 2 106.2, tt, J ¼ 5.5,
þ
.5 Hz. HRMS calcd. C H F NaO [2M þ Na] 747.3984; found
5
0
54
2
2
47.4026.
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8