New annulation techniques; Condensations of phosphonium ylides and substituted 2H-pyran-5-carboxylates; Preparation of cyclohexenonedicarboxylates and cyclohexadienedicarboxylates

Article abstract of DOI:10.1002/jccs.200300064

Substituted alkyl 2H-pyran-5-carboxylates condensed with alkyl 3-oxo-4-(triphenylphosphoranylidene)butanoate and alkyl 4- (triphenylphosphoranylidene)-2-butenoate to form substituted 2-vinyl-6-oxo-4cyclohexene-1,3-dicarboxylates, some of which showed ecto

Full text of DOI:10.1002/jccs.200300064

Journal of the Chinese Chemical Society, 2003, 50, 419-424
419
New Annulation Techniques; Condensations of Phosphonium Ylides and
Substituted 2H-Pyran-5-carboxylates; Preparation of
Cyclohexenonedicarboxylates and Cyclohexadienedicarboxylates
Cornelis M. Moorhoff
Department of Chemistry, University of Tasmania, GPO Box 252-75C, HOBART, Tasmania 7001, Australia
Substituted alkyl 2H-pyran-5-carboxylates condensed with alkyl 3-oxo-4-(triphenylphosphoranyl-
idene)butanoate and alkyl 4-(triphenylphosphoranylidene)-2-butenoate to form substituted 2-vinyl-6-oxo-4-
cyclohexene-1,3-dicarboxylates, some of which showed ecto-parasiticidal activity in pets and cattle, and sub-
stituted 2-vinyl-3,5-cyclohexadiene-1,3-dicarboxylates, respectively. The last mentioned product is in
marked contrast to the product obtained using the corresponding arsonium analogue.
Keywords: Alkyl 2H-pyran-5-carboxylates; Methyl 3-oxo-4-(triphenylphosphoranylidene)butanoate; Methyl
4-(triphenylphosphoranylidene)-2-butenoate; 2-Vinyl-6-oxo-4-cyclohexene-1,3-dicarboxylate;
2-Vinyl-3,5-cyclohexadiene-1,3-dicarboxylate.
Scheme I Condensation of arsonium ylids 3 and 6 and
2H-pyran-5-carboxylates 1
INTRODUCTION
New annulation techniques for the construction of sub-
COR1
COR1
stituted cyclohexenones1 and substituted cyclohexadienes2
are important in organic synthesis.Recently, we described the
condensations of arsonium ylides and 2H-pyran-5-carboxyl-
ates 1.3,4,5,6 2H-pyran-5-carboxylates 17 have the unique abil-
ity to undergo reversible electrocyclic ring opening to the
ketodiene 28 making these compounds available for Michael
attack. For example, methyl 3-oxo-4-(triphenylarsoranyl-
idene)butanoate 3 reacted with 2H-pyran-5-carboxylates 1
and gave mainly cyclohexenonedicarboxylates 4 and tetrahy-
drobenzofurandicarboxylates 5 (R2 = H) as a minor byprod-
uct4 (Scheme I). On the other hand, methyl 4-(triphenylar-
soranylidene)but-2-enoate 6 reacted with 2H-pyran-5-car-
boxylates 1 and gave mainly divinylcyclopropanecarboxyl-
ates 7.5 Tetrahydrobenzofurandicarboxylates 8 (R2 = H) were
in some cases also formed as a byproduct. (Scheme I).
In this paper we report on the Michael-Wittig conden-
sations of the phosphonium ylides namely, methyl 3-oxo-4-
(triphenylphosphoranylidene)butanoate 9a–9c and ethyl 4-
(triphenylphosphoranylidene)but-2-enoate 10 with substi-
tuted 2H-pyran-5-carboxylates 1.
X
X
+
R2
CO2Me
O
CO2Me
COR1
4
5
OH
O
X
X
a
a
g
g
Ph3As
CO2Me
O
Ph3P
Ph3P
CO2Me
R2
O
3
O
1
9
COR1
CO2Me
Ph3As
CO2Me
X
10
6
O
COR1
COR1
R2
2
X
+
R2
X = H, Cl, Br
O
R1 = OMe, SEt
R2 = H, Me
O
CO2Me
CO2Me
7
8
5-carboxylates 1 at room temperature,4 alkyl 3-oxo-4-(tri-
phenylphosphoranylidene)butanoates 9a, 9b and 9c9 reacted
with 2H-pyran-5-carboxylates 1a-1f in benzene only above
60 °C to form substituted dialkyl 2-vinyl-6-oxo-4-cyclo-
hexene-1,3-dicarboxylates 4a-4f in a mixture of three keto
diastereomers and one or two enol diastereomers (Scheme
II).4 Some retro-aldol took place with conjugated 2H-pyran-
5-carboxylates 1a-1c. No tetrahydrobenzofurans 54 were iso-
lated. The mechanism of this reaction can be formulated as
being the result of an initial Michael attack of the g-ylide
form of 9a (9b and 9c) on the ketoester 2. This is followed by
an intramolecular Wittig condensation and expulsion of
Ph3P=O to give 4a,10 4b, 4c,11 4d,4 4e4 and 4f (Table 1). Apart
from the esters of the phosphonium ylide 9a-9c,9 few other
RESULTS AND DISCUSSION
Although the arsonium ylide 3 reacted with 2H-pyran-
Present address: Boron Molecular Pty. Ltd., P.O. Box 756, Noble Park, VIC 3174, Australia

420 J. Chin. Chem. Soc., Vol. 50, No. 3A, 2003
Moorhoff
Scheme II Condensation of phosphonium ylide 9a-9c
with 2H-pyran-5-carboxylates 1
Scheme III Condensation of phosphonium ylide 10
with 2H-pyran-5-carboxylates 1
COR1
R2
COR1
H
COR1
COR1
H
COR1
COR1
3
R2
R2
R3
R3
R3
3
CgC3
CgC3
R2
O
O
O
O
O
O
R2
R2
2
2
Ph3P
CO2Et
Ph3P
COR4
1a R1 = OEt,
R2 = Me2C=CHCH=CH
1g R1 = OEt, R2 = Me
1h R1 = OPri,
R2 = Me2C=CHCH=CH
1i R1 = OBut, R2 = Me
1a R1 = OEt, R2 = Me,
O
Ph3P
COR4
COR4
g
Ph3P
CO2Et
CO2Et
g
R3 = Me2C=CHCH=CH
1b R1 = OMe, R2 = Me,
R3 = Me2C=CHCH=CH
1c R1 = OMe, R2 = H,
Wittig -Ph3P=O
O
O
-Ph3P=O
Wittig
R3
COR1
R2
COR1
Ph3P
a
Ph3P
a
R3 = MeCH=CHCH=CH
1d R1 = OMe, R2 = Me, R3 = Me
1e R1 = OMe, R2 = H, R3 = Me
1f R1 = OEt, R2 = H, R3 = Me
R2
COR4
10
CO2Et
9a
R
4 = OEt
11
9b R4 = OMe
O
9c9 4 = SEt
R
4
Table 2. Condensation Products Obtained from the Condensation of
phosphonium ylides are known that have been used for Mi-
chael-Wittig condensations for the production of cyclohex-
enone derivatives.12 No further condensation products were
identified.13 Biological screening tests revealed that cyclo-
hexenonedicarboxylates 4d and 4e showed some activity
against ectoparasites in pets and cattle.
Phosphonium Ylide 10 with 2H-pyran-5-carboxylates 1
No
R1
R2
Yield (%)
OEt
OEt
Me2C=CHCH=CH
Me
27
41
11a
11g
11h
11i
OPri
OBut
Me2C=CHCH=CH
Me
25
49
The Michael-Wittig condensation is now a well-estab-
lished useful synthetic reaction for the construction of 1,3-
cyclohexadienes.14 In this study we have found that alkyl 4-
(triphenylphosphoranylidene)-2-butenoate 10 reacted with
2H-pyran-5-carboxylates 1 in benzene at 60 °C to form sub-
stituted cyclohexa-3,5-diene-1,3-dicarboxylates 11 (Scheme
III). This is in sharp contrast to the condensation of the corre-
sponding arsonium ylide 6 which gave 2,3-divinylcyclopro-
pane-1-carboxylates 7.5 A solution of ethyl 2,2,6-trimethyl-
2H-pyran-5-carboxylate 1g was added to the phosphonium
ylide 10 in benzene and refluxed for 3 hours to give the sub-
stituted 3,5-cyclohexadiene-1,3-dicarboxylate 11g in a mod-
est yield of 41% (Table 2). A Cg-C3-Michael-attack of the
g-ylide of 10 on the ketodiene valence-tautomer of 1g fol-
lowed by an intramolecular Wittig condensation and elimina-
tion of triphenylphosphine oxide furnished the 3,5-cyclohex-
adiene-1,3-dicarboxylate 11g. The small coupling constant
of e.g. 11g (J = 1.2 Hz) of the two aliphatic protons in the ring
is consistent with the proposed stereochemistry of 11.15
EXPERIMENTAL SECTION
All reactions were carried out in a nitrogen atmosphere.
1H NMR and 13C NMR were recorded on a Varian FT-80 at 80
and 20 MHz, respectively, or on a Varian Gemini 200 spec-
trometer at 200 MHz and 50.3 MHz, respectively, in CDCl3
with TMS as an internal standard for 1H NMR. High resolu-
tion electron ionization (EI) mass spectra were obtained from
a Varian MAT 311 A instrument and high resolution chemical
ionization spectra (CI) using ammonia, were obtained from a
Table 1. Condensation Products Obtained from the Condensation of Phosphonium Ylids 9a–9c with 2H-pyran-5-carboxylates 1
No
R1
R2
R3
R4
Reaction conditions
Yield (%)
Ratio
4a10
4b
OEt
Me
Me
H
Me
H
Me2C=CHCH=CH
Me2C=CHCH=CH
MeCH=CHCH=CH
OEt
3 h, 130 °C, neat
7 h, 75 °C, C6H6
7 h, 70 °C, C6H6
5 h, 75 °C, C6H6
4 h, 75 °C, C6H6
5 h, 70 °C, C6H6
31a
35b
23c
24
33
3
9:22d
12:23d
7:16d
OMe
OMe
OMe
OMe
OEt
OMe
OMe
OMe
OMe
SEt
4c11
4d4
4e4
4f
Me
Me
Me
16:5:4e
8:3:1:1e
(-)
H
a,b,c 4%, 16% and 35% yield of retro-aldol products namely ethyl-, methyl 7-methyl-3-oxo-4,6-octadienoate11 and methyl 3-oxo-4,6-
octadienoate11 of respectively 2H-pyrans 4a, 4b and 4c. d Ratio enol:keto of 4a, 4b and 4c. e Ratio ketodiesters of 4d and 4e.

Michael-Wittig Condensations
J. Chin. Chem. Soc., Vol. 50, No. 3A, 2003 421
Table 3. 13C Chemical Shifts of Compounds 4f, 11a, 11b, 11c
Condensation of methyl 2,2-dimethyl-6-(4-methyl-
penta-1,3-dienyl)-2H-pyran-5-carboxylate 1b and
methyl 3-oxo-4-(triphenylphosphoranylidene)-
and 11da,e
21
21
21
19
O
3
O
17
O
3
17
O
17
O
O
19
7
19
butanoate 9b11
13
11
11
11
2
2
2
8
3
4
15
8
9
9
9
7
7
1
1
14
16
1
A mixture of methyl 3-oxo-4-(triphenylphosphoranyl-
idene)butanoate 9b (4.40 g, 10.6 mmol) and methyl 2,2-di-
methyl-6-(4-methylpenta-1,3-dienyl)-2H-pyran-5-carbox-
ylate 1b (2.36 g, 9.50 mol) in benzene (5 mL) was refluxed
for 7 hours in the presence of magnesium sulfate (4.00 g,
33.0 mmol) and hydroquinone (0.11 g, 1.0 mmol). The reac-
tion mixture was diluted with benzene:diethyl ether (2:3)
(50 mL) and filtered over silica gel. The filtrate was evapo-
rated and the residue chromatographed over silica gel and
eluted with diethyl ether:light petroleum (1:24), (2:23) and
(3:22) to (1:4) to give respectively the recovered 2H-pyran-
5-carboxylate 1b (0.23 g, 9.8%); methyl 7-methyl-3-oxo-
octa-4,6-dienoate (0.28 g, 16.2 %) and (1E) dimethyl 6-(4-
methylpenta-1,3-dienyl)-2-(2-methylprop-1-enyl)-4-
oxocyclohex-5-ene-1,3-dicarboxylate 4b (0.53 g, 35.2%) in
equilibrium with (1E) dimethyl 4-hydroxy-6-(4-methyl-
penta-1,3-dienyl)-2-(2-methylprop-1-enyl)cyclohexa-3,5-
diene-1,3-dicarboxylate tautomer. Compound 4b had iden-
tical spectroscopic measurements with 4b isolated from the
condensation of 3-methyl-2-butenal and phosphonium ylide
9b.11
8
12
4
10
10
18
18
18
6
6
6
4
O
S
O
5
5
5
O
O
O
O
20 22
20 22
20 22
4f
11a, 11h
11gc
11g, 11i
11hb 11ib
No
4fb
11ac
1
2
3
4
5
6
7
8
146.37
51.49
38.67
138.73
46.23
34.99
138.24
51.06
34.44
128.40
131.54
121.14
138.81
46.40
34.92
138.77
51.72
34.17
127.85
131.55
120.56
64.95
129.35
131.00
125.96
131.81
130.95
125.91
195.45
126.67
132.54
121.54
18.23
123.21*d 123.59
123.30*d 123.33
133.87
25.87,
26.30
133.57
25.84
133.84
25.95,
26.41
133.31
25.71
9, 15
10, 16
18.30,
18.72
128.27
132.07
123.84*
137.69
171.46
166.41
60.28,
60.82
18.18
23.86
18.31,
18.76
17.97
23.74
11
12
13
14
17
18
19, 20
23.23
128.29
132.15
123.86*
137.81
171.07
166.52
68.19,
60.32
164.55
191.81
61.62
24.59
14.67,
14.50
171.19
166.40
60.08,
60.70
14.15,
14.31
170.55
166.53
80.75
59.99
27.77
14.11
Condensation of methyl 2-methyl-6-(penta-1,3-dienyl)-
2H-pyran-5-carboxylate 1c and methyl 3-oxo-4-(triphen-
ylphosphoranylidene)butanoate 9b
21, 22
14.12,
14.28
21.69
14.32
a See Schemes II and III for compound numbers. At room
temperature in CDCl3 (d in ppm). b at 50 MHz. c at 20 MHz.
d Signals *can be interchanged. e NMR data of compounds 4d
and 4e are reported in the experimental and gave the same
chemical shifts as reported previously.4
A mixture of methyl 3-oxo-4-(triphenylphosphoranyli-
dene)butanoate 9b (13.9 g, 31.3 mmol) and methyl 2-meth-
yl-6-(penta-1,3-dienyl)-2H-pyran-5-carboxylate 1c (3.45 g,
15.7 mol) in benzene (20 mL) was refluxed for 4 hours in the
presence of sodium hydride (5 mg) and hydroquinone (1.70
g, 15.4 mmol). The reaction mixture was diluted with ben-
zene (40 mL) and filtered over silica gel. The filtrate was
evaporated and the residue chromatographed over silica gel
and eluted with diethyl ether:light petroleum (40-60 °C)
(1:24), (2:23) and (3:22) to (1:4) to give respectively the re-
covered 2H-pyran-5-carboxylate 1c (0.03 g, 0.9%); methyl
3-oxoocta-4,6-dienoate (0.93 g, 35.1 %) and (1E) dimethyl
6-(penta-1,3-dienyl)-2-(prop-1-enyl)-4-oxocyclohex-5-ene-
1,3-dicarboxylate 4c (1.13 g, 22.6%) in equilibrium with
(1E) dimethyl 4-hydroxy-6-(penta-1,3-dienyl)-2-(prop-1-
enyl)cyclohexa-3,5-diene-1,3-dicarboxylate tautomer. Com-
pound 4c had identical spectroscopic measurements with 4c
isolated from the condensation of crotonaldehyde and phos-
phonium ylide 9b.11
Kratos Concept ISQ instrument. Ultraviolet absorbance was
measured as solutions in 96% EtOH on a Varian SuperScan 3
spectrophotometer or on a Shimadzu UV-150 spectrophoto-
meter. Infrared spectra were obtained on a Hitachi 270-30
FTIR spectrophotometer (film, NaCl plates). Microanalyses
were performed by Microanalytisches Labor Pascher (Bonn,
Germany) or using a Carlo Erba, CHNS-O EA 1108 Elemen-
tal Analyser. Column chromatography was performed using
Merck Si-60 (40-63 mm) silica gel. Bulb-to-bulb distillations
(bp) were carried out on a Buchi GKR-51 apparatus. Diethyl
ether (ether) and tetrahydrofuran (THF) were dried and dis-
tilled from LiAlH4. Light petroleum is the fraction between
40-60 °C. 2H-Pyran-5-carboxylates 1 were synthesised from
b-ketoesters and a,b-unsaturated aldehydes.7

422 J. Chin. Chem. Soc., Vol. 50, No. 3A, 2003
Moorhoff
Table 4. 1H Chemical Shifts of Compounds (Structures Depicted with Table 3) 4f, 11a, 11g, 11h and 11ia,d
No
4fb
J
11ac
J
11gc
J
11hb
J
11ib
J
2
3
4
2.97
2.2-2.4
3.82
m
m
d, 6.9
3.34
3.9-4.4
d, 1.2
m
2.84
3.9-4.3
d, 1.2
m
3.35
4.06
d, 1.2
d, 11.0
2.77
4.01
s
d, 10.3
5
6
7
8
6.99
6.09
4.98
d, 5.8
d, 5.8
dm, 9.5
6.90
5.95
5.06
dd, 5.8, 0.5
dq, 5.8, 1.3
dm, 10.2
7.05
6.15
5.00
d, 6.1
d, 6.1
dm, 9.9
6.89
5.93
5.00
d, 5.7
dd, 5.7, 1.4
dm, 10.3
5.92
5.38
5.59
1.66
s
ddm, 15.0, 6.4
dq, 15.0, 6.7
d, 6.4
9
1.62
1.85
1.85
2x s
2x s
1.64
1.81
1.94
d, 1.3
d, 1.4
d, 1.3
1.64
1.91
1.82
1.83
6.25
d, 1.3
s
2x s
1.61
1.76
1.90
s
s
s
15
10
16
11
12
13
19
20
21
22
2.03
s
6.18
6.57
5.87
4.06
4.15
1.17
1.26
d, 15.0
dd, 15.0, 10.2
dm, 10.2
d, 15.3
6.60 dd, 15.3, 10.7
5.93
4.96
4.17
1.18
1.26
dm, 10.7
h, 6.2
q, 7.2
d, 6.2
t, 7.2
4.16
2.94
1.24
1.28
q, 7.1
q, 7.4
t, 7.1
t, 7.4
2x q, 7.0
4.09
4.15
1.20
1.24
2x q, 7.1
2x t, 7.1
-
-
4.13
1.38
1.23
q, 7.2
s
t, 7.2
2x t, 7.0
a At room temperature in CDCl3 (d in ppm). b at 200 MHz. c at 80 MHz. d NMR data of compounds 4d and 4e is reported in the
experimental and gives the same chemical shifts as reported previously.4
Condensation of methyl 2,2,6-trimethyl-2H-pyran-5-
carboxylate 1d and methyl 3-oxo-4-(triphenylphos-
phoranylidene)butanoate 9b
7.32. This compound 4d was identical to 4d obtained from
the condensation of 1d and the arsonium ylide 3.4
A mixture of methyl 3-oxo-4-(triphenylphosphoranyli-
dene)butanoate 9a (2.80 g, 6.74 mmol) and methyl 2,2,6-
trimethyl-2H-pyran-5-carboxylate 1d (1.15 g, 6.31 mol) in
benzene (10 mL) was heated for 5 hours at 75 °C in the pres-
ence of hydroquinone (1.00 g, 9.08 mmol). The reaction mix-
ture was diluted with light petroleum:diethyl ether (1:1) (50
mL) and filtered over silica gel. The filtrate was evaporated
and the residue chromatographed over silica gel and eluted
with diethyl ether:light petroleum (40-60 °C) (1:19), (1:9)
and (1:3) to give recovered 2,6,6-trimethyl-2H-pyram-5-car-
boxylate 1d (80 mg, 7.0%), 3-(methoxycarbonyl)-6-methyl-
hepta-3,5-diene (30 mg, 2.6%) and dimethyl 6-methyl-2-(2-
methylprop-1-enyl)-4-oxocyclohex-5-ene-1,3-dicarboxylate
4 4d (0.42 g, 23.8%). bp 125 °C (airbath) at 10-5 mm Hg. lmax
= 231, 316 (e = 11270, 1660). 1H NMR (major keto isomer,
64%): d 1.64 (3H, d, J = 1.5 Hz), 1.68 (3H, d, J = 1.4 Hz), 1.96
(3H, d, J = 3.6 Hz), 3.17 (1H, dd, J = 12.5, 0.4 Hz), 3.53-3.85
(2H, m), 3.69 and 3.71 (6H, 2s), 4.95 (1H, dm, J = 9.7 Hz),
6.01 (1H, sm); 13C NMR: d 17.85 (CH3), 21.89 (CH3), 25.78
(CH3), 40.70 (CH), 51.78 and 52.03 (2x MeO), 53.11 (CH),
58.56 (CH), 122.50 (CH), 127.27 (CH), 137.31 (C) 157.09
(C), 169.45 (C=O), 171.53 (C=O), 192.28 (C=O); HRMS
(EI) calcd. for C15H20O5 m/z 280.1311, found 280.1309. Anal.
Calcd. for C15H20O5: C, 64.27; H, 7.19. Found: C, 64.09; H,
Condensation of methyl 2,6-dimethyl-2H-pyran-5-
carboxylate 1e and methyl 3-oxo-4-(triphenylphos-
phoranylidene)butanoate 9a
A mixture of methyl 3-oxo-4-(triphenylphosphoranyli-
dene)butanoate 9a (2.80 g, 6.74 mmol) and methyl 2,6-di-
methyl-2H-pyran-5-carboxylate 1e (0.90 g, 5.35 mol) in ben-
zene (6 mL) was heated for 4 hours at 75 °C in the presence of
hydroquinone (0.90 g, 8.17 mmol). The reaction mixture was
diluted with light petroleum:diethyl ether (1:1) (50 mL) and
filtered over silica gel. The filtrate was evaporated and the
residue chromatographed over silica gel and eluted with di-
ethyl ether:light petroleum (1:3) to give dimethyl 6-methyl-
2-(prop-1-enyl)-4-oxocyclohex-5-ene-1,3-dicarboxylate4 4e
(0.47 g, 33.0%). bp 115 °C (airbath) at 10-5 mm Hg. lmax
=
1
229, 317 (e = 11060, 860). H NMR (major keto isomer,
62%): d 1.63 (3H, d, J = 5, 1.5 Hz), 1.92 (3H, s), 2.95-3.9 (3H,
m), 3.71 and 3.68 (6H, 2s), 5.1-5.6 (2H, m), 5.93 (1H, sm).
13C NMR: d 17.88 (CH3), 22.08 (CH3), 44.55 (CH), 52.04 and
52.16 (2x MeO), 52.99 (CH), 58.25 (CH), 127.37 (CH),
128.36 (CH), 130.25 (CH), 156.74 (C), 169.38 (C=O), 171.37
(C=O), 192.19 (C=O); HRMS (EI) calcd. for C14H18O5 m/z
266.1154, found 266.1153. Anal. Calcd. for C14H18O5: C,
63.14; H, 6.81. Found: C, 62.78; H, 6.89. This compound 4e
gave identical data to 4e obtained from the condensation of

Michael-Wittig Condensations
J. Chin. Chem. Soc., Vol. 50, No. 3A, 2003 423
1e and the arsonium ylide 3.4
but-3-enoate 10 (0.70 g, 1.87 mmol) and ethyl 2,2,6-trimeth-
yl-2H-pyran-5-carboxylate 1g (0.48 g, 1.83 mmol) in ben-
zene (5 mL) was refluxed for 8 hours in the presence of
hydroquinone (0.1 g, 0.91 mmol). The reaction mixture was
diluted with light petroleum:diethyl ether (1:1) (100 mL) and
filtered over silica gel. The filtrate was evaporated and the
residue chromatographed over silica gel and eluted with di-
ethyl ether:light petroleum (40-60 °C) (3:17), diethyl 6-
methyl-2-(2-methylprop-1-enyl)-3,5-cyclohexadiene-1,3-
dicarboxylate 11g 0.76 g, 40.8%). bp 125 °C (airbath) at 0.04
mm Hg. lmax = 296 (e = 7030). HRMS (EI) calcd. for
C17H24O4 m/z 292.1674, found 292.1702. Anal. Calcd. for
C17H24O4: C, 69.84; H, 8.27. Found: C, 69.55; H, 8.22.
Condensation of ethyl 2,6-trimethyl-2H-pyran-5-
carboxylate 1f and S-ethyl 3-oxo-4-(triphenylphos-
phoranylidene)butanoate 9c9
A mixture of crude S-Ethyl 3-oxo-4-(triphenylphos-
phoranylidene)butanoate 9c9 (15 g, 0.037 mol) and ethyl
2,6-trimethyl-2H-pyran-5-carboxylate 1f (1.1 g, mol) in ben-
zene (150 mL) was heated for 6 hours at 75 °C in the presence
of hydroquinone (0.90 g, 8.17 mmol). The mixture was di-
luted with light petroleum:diethyl ether (1:1) (50 mL) and fil-
tered over silica gel. The filtrate was evaporated and the resi-
due chromatographed over silica gel and eluted with diethyl
ether:light petroleum (1:9) and (3:7) to give respectively
uncharacterized sulphurous compounds including some
unreacted 2H-pyran-5-carboxylate 1f and 1-ethyl,3-S-Ethyl
6-methyl-2-(prop-1-enyl)-4-oxocyclohex-5-ene-1,3-dicar-
boxylate 4f (0.35 g, 3.1 %). bp 115 °C (airbath) at 10-2 mm
Hg. lmax = 206 (sh), 234, 344 (e = 7300, 9900, 2700). IR lmax
(film) = 2978 (m), 2933 (m), 1733 (s), 1666 (s), 1634 (m),
1582 (s), 1445 (m), 1378 (m), 1191 (s), 1158 (m), 1032 (m),
967 (m) cm-1. HRMS (EI) calcd. for C16H22O4S m/z 310.1239,
found 310.1243. MS: 310 (10), 282 (5), 249 (50), 221 (10),
175 (20), 95 (100). Anal. Calcd. for C16H22O4S: C, 61.91; H,
7.14; S, 10.33. Found: C, 61.82; H, 7.41; S, 10.01.
Condensation of 1-methylethyl 2,2-dimethyl-6-(4-methyl-
penta-1,3-dienyl)-2H-pyran-5-carboxylate 1h and ethyl
4-(triphenylphosphoranylidene)but-3-enoate 10
A mixture of ethyl 4-(triphenylphosphoranylidene)but-
3-enoate 10 (0.55 g, 1.47 mmol) and 1-methylethyl 2,2-di-
methyl-6-(4-methylpenta-1,3-dienyl)-2H-pyran-5-carboxyl
ate 1h (0.25 g, 0.905 mmol) in benzene (1 mL) was heated for
75 minutes at 75 °C in the presence of hydroquinone (0.11 g,
1.0 mmol). The reaction mixture was diluted with light petro-
leum:ethyl acetate (1:1) (50 mL) and filtered over silica gel.
The filtrate was evaporated and the residue chromatographed
over silica gel and eluted with ethyl acetate:light petroleum
(40-60 °C) (1:9), (1E) 3-(1-methylethyl),1-ethyl 6-(4-meth-
ylpenta-1,3-dienyl)-2-(2-methylprop-1-enyl)-3,5-cyclohex-
adiene-1,3-dicarboxylate 11h (0.085 g, 25.2%). IR (cm-1):
nmax 2983 (s); 2933 (s); 2875 (m); 1730 (s); 1710 (s); 1631
(m); 1448 (m); 1375 (m); 1259 (s); 1108 (s).
Condensation of ethyl 2,2-dimethyl-6-(4-methylpenta-1,3-
dienyl)-2H-pyran-5-carboxylate 1a and ethyl 4-(triphen-
ylphosphoranylidene)but-3-enoate 10
A mixture of ethyl 4-(triphenylphosphoranylidene)-
but-3-enoate 10 (5.0 g, 13.3 mmol) and ethyl 2,2-dimethyl-
6-(4-methylpenta-1,3-dienyl)-2H-pyran-5-carboxylate 1a
(1.25 g, 6.37 mol) in benzene (10 mL) was heated for 15
hours at 75 °C in the presence of hydroquinone (0.11 g, 1.0
mmol). The reaction mixture was diluted with benzene: di-
ethyl ether (1:1) (50 mL) and filtered over silica gel. The fil-
trate was evaporated and the residue chromatographed over
silica gel and eluted with diethyl ether:light petroleum (40-60
°C) (1:19) to give (1E) diethyl 6-(4-methylpenta-1,3-di-
enyl)-2-(2-methylprop-1-enyl)-3,5-cyclohexadiene-1,3-di-
carboxylate 11a (0.18 g, 27.4%). bp 120 °C (airbath) at 0.04
mm Hg. lmax = 371, 248 (e = 19750, 10390). HRMS (EI) calcd.
for C22H30O4 m/z 358.2144, found 358.2167. Anal. Calcd. for
C22H30O4: C, 72.70; H, 7.93. Found: C, 72.59; H, 8.07.
Condensation of 1,1-Dimethylethyl 2,2,6-trimethyl-2H-
pyran-5-carboxylate 1i and ethyl 4-(triphenylphos-
phoranylidene)but-3-enoate 10
A mixture of ethyl 4-(triphenylphosphoranylidene)-
but-3-enoate 10 (0.48 g, 1.28 mmol) and t-butyl 2,2,6-tri-
methyl-2H-pyran-5-carboxylate 1i (0.17 g, 0.7578 mmol) in
benzene (1 mL) was heated at 75 °C for 2 hours in the pres-
ence of hydroquinone (0.1 g, 0.91 mmol). The reaction mix-
ture was diluted with light petroleum:ethyl acetate (1:1) (100
mL) and filtered over silica gel. The filtrate was evaporated
and the residue chromatographed over silica gel and eluted
with ethyl acetate:light petroleum (40-60 °C) (1:9) to give
3-(1,1-dimethylethyl)-1-ethyl 6-methyl-2-(2-methylprop-1-
enyl)-3,5-cyclohexadiene-1,3-dicarboxylate 11i (0.12 g,
49.4%). bp 125 °C (airbath) at 0.04 mm Hg. lmax = 299.5. IR
(cm-1): nmax 2984 (s), 2960 (s), 1710 (s), 1706 (s), 1615 (m),
1590 (m), 1445 (m), 1368 (m), 1263 (s), 1142 (s), 842 (m),
Condensation of ethyl 2,2,6-trimethyl-2H-pyran-5-
carboxylate 1g and ethyl 4-(triphenylphosphoranyli-
dene)but-3-enoate 10
A mixture of ethyl 4-(triphenylphosphoranylidene)-

424 J. Chin. Chem. Soc., Vol. 50, No. 3A, 2003
Moorhoff
757 (m). Found: MH+ (LSIMS), 321.20596. C19H29O4 re-
quires M, 321.20659.
2. (a) Pramod, K.; Ramanathan, H.; Rao, G. S. R. S. J. Chem.
Soc. Perk. Trans. 1 1983, 7. (b) Buchi, G.; Wuest, H. Helv.
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I. N.; Serebryakov, E. P. Russ. Chem. Bull. 1996, 45, 144.
3. Moorhoff, C. M. Tetrahedron Lett. 1996, 37, 9349.
4. Moorhoff, C. M. Tetrahedron 1997, 53, 2241.
ACKNOWLEDGMENTS
5. Moorhoff, C. M. J. Chem. Res. (M) 1997, 866. J. Chem. Res.
(S) 1997, 130.
6. Moorhoff, C. M.; Winkler, D. New J. Chem. 1998, 12, 1485.
7. Moorhoff, C. M. Synthesis 1997, 685.
8. (a) Gosink, T. A. J. Org. Chem. 1974, 39, 1942. (b) Boehm,
S.; Kuthan, J. Collect. Czech. Chem. Commun. 1983, 48,
1007 (Chem. Abstr. 1983, 99, 87336).
9. Moorhoff, C. M. J. Chem. Soc., Perk. Trans. 1 1997, 1987.
10. Moorhoff, C. M.; Schneider, D. F. Tetrahedron Lett. 1987,
28, 4721.
11. Moorhoff, C. M.; Schneider, D. F.; Winkler, D. J. Chem. Res.
(M) 1998, 3461. J. Chem. Res. (S) 1998, 763.
12. (a) Broquet, C. Tetrahedron 1975, 31, 1331. (b) Martin, S.
F.; Desai, S. R. J. Org. Chem. 1977, 42, 1664. (c) Martin S.
F.; Desai, S. R. J. Org. Chem. 1978, 43, 4673.
The author thanks David Schneider (University of
Stellenbosch) for helpful discussions during the developmen-
tal stages of this project; Dr. Graham Rowbottom (University
of Tasmania) and Microanalitisches Labor Pascher for ele-
mental analyses; Hendrik Spies (University of Stellenbosch)
for NMR-analyses of compounds 4d, 4e, 11a and 11g; Verona
Truter (University of Stellenbosch) and Dr. Noel Davies
(University of Tasmania) for mass spectral analyses; Novartis
Australasia for testing of compounds. Financial assistance
from the Foundation for Research Development (South Af-
rica) and Australian Research Council is gratefully acknowl-
edged.
13. Yang, J-D.; Kim, M-S.; Lee, M.; Baik W.; Koo, S. Synthesis
2000, 801.
Received May 28, 2002.
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