Ruthenium-catalyzed addition of carboxylic acids or cyclic 1,3-dicarbonyl compounds to propargyl alcohols

Article abstract of DOI:10.1016/j.tetlet.2010.10.053

Monomeric ruthenium(O) complexes containing redox-coupled dienone ligands were found to catalyze the regio-selective addition of carboxylic acids or cyclic 1,3-dicarbonyl compounds to propargyl alcohols.

Full text of DOI:10.1016/j.tetlet.2010.10.053

Tetrahedron Letters 51 (2010) 6630–6634
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Ruthenium-catalyzed addition of carboxylic acids or cyclic 1,3-dicarbonyl
compounds to propargyl alcohols
⇑
Stefanie Berger, Edgar Haak
Institut für Chemie der Otto-von-Guericke-Universität Magdeburg, Universitätsplatz 2, 39106 Magdeburg, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
Monomeric ruthenium(0) complexes containing redox-coupled dienone ligands were found to catalyze
the regio-selective addition of carboxylic acids or cyclic 1,3-dicarbonyl compounds to propargyl alcohols.
Ó 2010 Elsevier Ltd. All rights reserved.
Received 3 August 2010
Revised 7 October 2010
Accepted 11 October 2010
Available online 16 October 2010
Keywords:
Addition
Homogeneous catalysis
Propargyl alcohols
Ruthenium
Vinylidene complexes
1. Introduction
carboxylic acids like cyclic 1,3-dicarbonyl compounds pyran struc-
tures are obtained. Two related ruthenium-catalyzed reactions
Several ruthenium complexes catalyze the Markovnikov addi-
tion of carboxylic acids to alkynes.1 The analogue addition to
propargyl alcohols leads to b-oxopropyl esters by an addition
trans-esterification sequence.2 Ruthenium complexes that cata-
lyze the anti-Markovnikov addition of acids to alkynes remains
limited to a few electron rich examples.3 Concerning the ruthe-
nium-catalyzed anti-Markovnikov addition of carboxylic acids to
propargyl alcohols Dixneuf and co-workers reported the addition
of benzoic acid to terminal tertiary propargyl alcohols using
have been described. Nishibayashi and co-workers reported the
formation of pyran compounds from terminal secondary aromatic
propargyl alcohols and cyclic 1,3-dicarbonyl compounds catalyzed
by dimeric thiolate bridged complexes.6 Gimeno and co-workers
reported a ruthenium-catalyzed pyran ring formation from termi-
nal or internal secondary aromatic propargyl alcohols with 1,3-
cyclopentanedione while different 1,3-dicarbonyl compounds led
to furan ring formation instead.7
Ru(g
3-methallyl)2(dppe) as the precatalyst.4 The latter reaction
2. Results and discussion
shows a stereo-selectivity favoring the formation of (Z)-hydroxy
enolesters.
The ruthenium-catalyzed addition of carboxylic acids to terminal
tertiary aromatic or aliphatic propargyl alcohols using 1a
(R = R0 = Ph) or 1b (R = H, R0 = Me) as catalysts leads to high regio-
and stereo-selectivity to (E)-hydoxy enolesters (3). Terminal sec-
ondary propargyl alcohols form b-oxopropyl esters (4) as well due
to low regioselectivity (Scheme 1, Table 1). Internal propargyl alco-
hols remain unreactive under the same reaction conditions. The
transformation does not occur in the absence of the ruthenium
catalyst.
Cyclic 1,3-dicarbonyl compounds add to terminal propargyl
alcohols in the presence of 1a or 1b (2 mol %) to form pyran com-
pounds (5) in some cases accompanied by methylene dihydrofuran
byproducts (6), other regioisomeric products were not detected.
With 1,3-cyclopentanedione the reaction proceeds without an
additive, otherwise CF3COOH (TFA) was used as co-catalyst
(2 mol %) (Scheme 2, Table 2).
Ruthenium cyclopentadienone derivatives provide unique fea-
tures toward catalytic transformations of bi-functional substrates
due to the redox-coupling of the dienone ligand and its basic co-
ordination site. We reported previously that complexes of type 1
catalyze the formation of a- or b-amino ketones, enamino ketones,
aldehydes, ketones, imines, enynes, alkenes, and allenyl carba-
mates from propargyl alcohols.5
While extending our studies on new metal-catalyzed transfor-
mations of propargyl compounds we have now discovered that
complexes of type 1 catalyze the anti-Markovnikov addition of car-
boxylic acids to propargyl alcohols. In contrast to the Dixneuf-sys-
tem4 only (E)-hydroxy enolesters are formed. With vinylogous
⇑
Corresponding author. Tel.: +49 391 67 11413; fax: +49 391 67 12223.
E-mail address: edgar.haak@ovgu.de (E. Haak).
0040-4039/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2010.10.053

S. Berger, E. Haak / Tetrahedron Letters 51 (2010) 6630–6634
6631
R1 R2
OH
2 mol-% 1
R1
R2
R3
O
R1
R2
R3COOH
O
O
+
N
toluene, 100°C, 3 h
OH
3
2
2
N
R'
traces
O
major product
R
O
R1
Ru
2 mol-% 1
R3COOH
OC
R1
O
CO
OC
OH
H
R3
R3
O
1
+
toluene, 100°C, 3 h
OH
O
R1
O
3
4
Scheme 1. Ruthenium-catalyzed addition of carboxylic acids to propargyl alcohols.
Table 1
Addition of carboxylic acids catalyzed by 1a
Secondary and tertiary aromatic or aliphatic terminal propargyl
alcohols are suitable substrates while various internal aliphatic
propargyl alcohols remain unreactive. Aliphatic propargyl alcohols
are not transformed in the absence of the ruthenium complex. The
reaction course of internal aromatic propargyl alcohols depends on
the nature of the substrate. Secondary alcohols like 2q lead to mix-
tures of enones (7) and pyran compounds (5), while tertiary alco-
hols like 2s form enynes (8), dihydrofuran products (6), and the
regioisomeric pyran compounds 9 accompanied by isomers like
10 in some cases (Scheme 3).
Aromatic propargyl alcohols undergo TFA-catalyzed benzylic
substitution without the ruthenium catalyst to yield the propargy-
lated compound 11, as the sole product in case of secondary educt
2q (Scheme 4). The acid catalyzed dehydration of 2s to yield 8s and
the following cycloaddition of 8s with phenols to yield 2-H-chrom-
enes was reported previously by Sartori and co-workers and is clo-
sely related to the formation of compound 9.8
Pyran ring formation from acyclic 1,3-dicarbonyl compounds
that form inner chelates in unpolar solvents was not observed. Ter-
minal aliphatic propargyl alcohols like ethynylcyclohexanol (2c)
form conjugated enynes 8 accompanied by terminal alkenes 12
in the absence of a suitable nucleophile instead (Scheme 5). This
transformation does not occur without the ruthenium catalyst.
Ruthenium-catalyzed formation of pyrans or furans from enyne
8c and 1,3-dicarbonyl compounds in the presence of 1a (2 mol %)
and TFA (2 mol %) could not be detected.
Entry
R1
R2
R3
Yield 3 (%)
Yield 4 (%)
a
b
c
d
e10
f
Me
Et
C5H10
Ph
Me
Ph
Me
Me
Me
Me
Me
Me
Me
Me
52
88
85
69
43
30
53
48
71
64
<1
<1
<1
<1
48
59
<1
<1
<1
<1
Me
H
H
g
Et
C5H10
Et
Me
CH@CH2
CH@CH2
CH@CHPh
CH@CHPh
h
i
Me
j10
C5H10
R1
R2
O
+
CH2
OH
2
O
2 mol-% 1
2 mol-% TFA (exept for a-f)
toluene, 100°C, 3 h
O
O
+
R2
R1
R1 R2
O
O
5
6
Scheme 2. Ruthenium-catalyzed addition of 1,3-dicarbonyl compounds to terminal
propargyl alcohols.
Table 2
Addition of 1,3-dicarbonyl compounds to terminal propargyl alcohols catalyzed by 1a
Entry
R1
R2
1,3-Dicarbonyl compound
Yield 5 (%)
Yield 6 (%)
a
Me
Et
Me
Me
48
86
<1
<1
O
O
O
b10
c
C5H10
Ph
Me
84
61
45
71
<1
12
<1
<1
d10
e
Me
H
H
R2
R1
O
R1 R2
O
O
f10
Ph
g
Me
Et
C5H10
Ph
Me
Ph
Me
Me
51
86
80
60
44
62
<1
<1
<1
10
<1
<1
O
O
O
h
i10
j
R2
Me
H
H
R1
R1 R2
O
O
O
k
l
O
O
O
m
Et
C5H10
Me
55
49
10
13
n10
R2
R1
R1 R2
O
O
O
O
O
O
O
o10
p
Et
C5H10
Me
73
67
12
16
O
O
O
O
R2
R1
R1 R2
O

6632
S. Berger, E. Haak / Tetrahedron Letters 51 (2010) 6630–6634
O
O
O
O
Ph
Ph
+
+
+
+
Ph
Ph
Ph
)-6s
O
5q
Ph
(54 %)
O
O
8s
7q
(26 %)
(19 %)
(
E
(7 %)
(Z)-6s (9 %)
9s (41 %)
O
O
O
OH
OH
2 mol-% 1a
2 mol-% TFA
toluene, 100°C, 3 h
1a
2 mol-%
O
O
O
10s
2 mol-% TFA
Ph
Ph
toluene, 100°C, 3 h
(12 %)
2s
2q
1a
2 mol-% 1a
2 mol-% TFA
toluene, 100°C, 3 h
2 mol-%
2 mol-% TFA
toluene, 100°C, 3 h
O
O
O
O
O
+
Ph
+
+
Ph
O
O
O
Ph
Ph
O
O
Ph
O
7q (8 %)
5r10
8s
9t (22 %)
(82 %)
(35 %)
(E)-6t (37 %)
(Z)-6t (<1 %)
Scheme 3. Transformations of internal aromatic propargyl alcohols.
OH
H
O
OH
OH
2c
O
Ph
Ph
2 mol-% 1a
2q
2s
O
2 mol-% TFA
C6D6, 80°C, 2 h
2 mol-% TFA
toluene, 100°C, 3 h
H
+
OH
OH
Ph
8c (59 %)
12c (38 %)
O
O
Scheme 5. Formation of enyne 8c and alkene 12c.
Ph
(34 %)
(39 %) + (12 %)
O
O
11r
11t
(22 %)
+
8s
9t
Scheme 4. TFA-catalyzed benzylic substitution.
N
R1
R2
O
N
R'
OH
R3
O
R
O
Ru
OC
R1 R2
O
CO
O
OC
5
3
- CO
N
N
N
N
R'
OH
R'
OH
N
N
R'
R
R
Ru
Ru
OC
O
O
OC
OC
OC
R
O
O
Ru
OC
R1
R2
OC
R3
H
R1
OH
OH
R2
O
R2
D
E
R1
2
N
N
N
N
R'
N
R'
O
N
R'
H
H
H
- H2O
R
O
O
R
O
R
O
O
Ru
OC
Ru
Ru
OC
OC
OC
O
H
R3
C
OC
C
OC
R2
C
R2
R1
O
B
H
A
O
C
R1
R2
OH
O
O
R1
HO
R3
Scheme 6. Postulated catalytic cycles for terminal substrates.

S. Berger, E. Haak / Tetrahedron Letters 51 (2010) 6630–6634
6633
[RuLOH(CO)n]
ways. Mechanistic details regarding intermediates of the catalytic
cycles, stereochemical aspects, redox-coupling of the dienone li-
gand, and the role of its basic co-ordination site are currently under
investigation.
[RuLO(CO)n]
O
OH
a
b
R = H
b
H
Ph
F
R
O
Ph
O
G
4. General procedure
a
≠
R
H
Compound 1a (0.02 mmol) was dissolved in toluene (1 mL)
mixed with a solution of TFA in toluene (20 lL, 1 M) if necessary
[RuLOH(CO)n]
O
O
and propargyl alcohol (1 mmol) as well as the nucleophilic compo-
nent (1 mmol) were added. The mixture was stirred at 100 °C for
3 h under argon. Aqueous work-up and chromatography on silica
furnished the purified products.
R
[RuLOH(CO)n]
Ph
O
O
Ph
H
5
- [RuLO(CO)n]
- [RuLO(CO)n]
Acknowledgment
6
N
N
Constant support by the Fonds der Chemischen Industrie is
gratefully acknowledged.
N
N
R'
OH
R'
LO
=
LOH
=
R
R
O
References and notes
Scheme 7. Postulated transformation of internal aromatic substrates.
1. (a) Bruneau, C.; Dixneuf, P. H. Angew. Chem., Int. Ed. 2006, 45, 2176–2203; (b)
Fischmeister, C.; Bruneau, C.; Dixneuf, P. H. In Ruthenium in Organic Synthesis;
Murahashi, S.-I., Ed.; Wiley-VCH: Weinheim, 2004; pp 189–217; (c) Bruneau,
C.; Neveux, M.; Kabouche, Z.; Ruppin, C.; Dixneuf, P. H. Synlett 1991, 755–763;
(d) Bruneau, C.; Dixneuf, P. H. Chem. Commun. 1997, 507–512; (e) Dixneuf, P.
H.; Bruneau, C. In Transition Metal Catalyzed Reactions; Murahashi, S.-I., Davis, S.
G., Eds.; Blackwell: Oxford, 1999; pp 391–404.
2. (a) Mitsudo, T.; Hori, Y.; Yamakawa, Y.; Watanabe, Y. J. Org. Chem. 1987, 52,
2230–2239; (b) Devanne, D.; Ruppin, C.; Dixneuf, P. H. J. Org. Chem. 1988, 53,
925–926; (c) Bruneau, C.; Kabouche, Z.; Neveux, M.; Seiller, B.; Dixneuf, P. H.
Inorg. Chim. Acta 1994, 222, 155–163.
3. (a) Doucet, H.; Höfer, J.; Bruneau, C.; Dixneuf, P. H. J. Chem. Soc., Chem. Commun.
1993, 850–851; (b) Tokunaga, T.; Suzuki, T.; Koga, N.; Fukushima, T.; Horiuchi,
A.; Wakatsuki, Y. J. Am. Chem. Soc. 2001, 123, 11917–11924; (c) Doucet, H.;
Martin-Vaca, B.; Bruneau, C.; Dixneuf, P. H. J. Org. Chem. 1995, 60, 7247–7255;
(d) Gemel, C.; Trimmel, G.; Slugovc, C.; Kremel, S.; Mereiter, K.; Schmid, R.;
Kirchner, K. Organometallics 1996, 15, 3998–4004; (e) Melis, K.; Samulkiewiecz,
P.; Rynkowski, J.; Verpoort, F. Tetrahedron Lett. 2002, 43, 2713–2716; (f)
Goossen, L. J.; Paetzold, J.; Koley, D. Chem. Commun. 2003, 706–707.
4. (a) Picquet, M.; Bruneau, C.; Dixneuf, P. H. Chem. Commun. 1997, 1201–1202;
(b) Picquet, M.; Fernandez, A.; Bruneau, C.; Dixneuf, P. H. Eur. J. Org. Chem. 2000,
2361–2366.
5. (a) Haak, E. Synlett 2006, 1847–1848; (b) Haak, E. Eur. J. Org. Chem. 2007, 2815–
2824; (c) Haak, E. Eur. J. Org. Chem. 2008, 788–792.
6. Nishibayashi, Y.; Yoshikawa, M.; Inada, Y.; Hidai, M.; Uemura, S. J. Org. Chem.
2004, 69, 3408–3412.
7. Cadierno, V.; Díez, J.; Gimeno, J.; Nebra, N. J. Org. Chem. 2008, 73, 5852–5858.
8. Bigi, F.; Carloni, S.; Maggi, R.; Muchetti, C.; Sartori, G. J. Org. Chem. 1997, 62,
7024–7027.
9. Casey, C. P.; Jiao, X.; Guzei I. A. Organometallics 2010, 29. doi:10.1021/
om100012j.
Due to the fact that internal aliphatic propargyl alcohols as well
as aliphatic enynes like 8c remain unreactive and in accordance
with our previous results5 we assume that the ruthenium-cata-
lyzed-additions of carboxylic acids or cyclic 1,3-dicarbonyl com-
pounds to terminal propargyl alcohols are initiated by chelating
co-ordination of the propargyl alcohol to the 16-electron metal
species (A) followed by the formation of ruthenium vinylidene
complex B or allenylidene species C. Nucleophilic addition of a li-
gand-co-ordinated carboxylic acid at the C atom of vinylidene
a
complex B should occur trans-selective from the less hindered site
to give alkenyl complex D that liberates product 3. Nucleophilic
addition of a co-ordinated cyclic 1,3-dicarbonyl compound should
occur at the C atom of allenylidene complex C followed by cycli-
c
zation of the resulting vinylidene species to give alkenyl complex
E (Scheme 6).
The side products 4 and 6 could be driven from
p-complexed
terminal alkynes (analogues to A) that may be formed from vinyl-
idene intermediates. The TFA needed as a co-catalyst in some cases
may enhance the solubility of cyclic 1,3-diketones in toluene, pro-
mote the dehydration step of the allenylidene formation, and en-
hance the electrophilicity of the ruthenium center by protonation
of the dienone ligand.
The transformation of internal aromatic propargyl alcohols may
be initiated by TFA-catalyzed benzylic substitution. The following
10. Data of selected compounds
Compound 3e (C6H10O3): 1H NMR (400 MHz, CDCl3): d = 1.35 (d, J = 7.1 Hz, 3H),
2.13 (s, 3H), 5.39 (dq, J = 7.6, 7.1 Hz, 1H), 5.46 (dd, J = 12.3, 7.6 Hz, 1H), 7.37 (d,
J = 12.3 Hz, 1H) ppm. 13C NMR (100 MHz, DEPT, CDCl3): d = 20.7 (CH3), 21.3
(CH3), 67.6 (CH), 114.1 (CH), 138.2 (CH), 167.7 (C) ppm. MS (EI): m/z 130 [M+].
HRMS: calcd: 130.06299, found: 130.06276.
ruthenium-catalyzed cyclization could occur from the
p-com-
plexed alkyne F leading to methylene dihydrofuran compound 6
in case of quartary substrates like 11t (Scheme 6, pathway a). Ter-
tiary substrates like 11r may undergo a 1,2-hydrogene shift prior
to cyclization of the resulting unsaturated alkenyl complex G to
give allyl complex H that liberates pyran compound 5 (Scheme 7,
pathway b). A related hydrogene shift was reported previously.5b,9
Competing hydrolysis of the alkenyl intermediate leads to Meyer-
Schuster product 7.
Compound 3j (C17H20O3): 1H NMR (400 MHz, CDCl3): d = 1.26–1.70 (m, 10H),
5.71 (d, J = 12.5 Hz, 1H), 6.46 (d, J = 16.0, 1H), 7.40–7.42 (m, 3H), 7.51 (d,
J = 12.5 Hz, 1H), 7.54–7.56 (m, 2H), 7.78 (d, J = 16.0 Hz, 1H) ppm. 13C NMR
(100 MHz, DEPT, CDCl3): d = 22.0 (CH2), 25.4 (CH2), 38.2 (CH2), 70.4 (C), 117.3
(CH), 122.6 (CH), 128.2 (CH), 128.9 (CH), 130.7 (CH), 134.1 (C), 135.9 (CH),
146.9 (CH), 164.1 (C) ppm. MS (EI): m/z 272 [M+]. HRMS: calcd: 272.14124,
found: 272.14139.
Compound 5b (C11H14O2): 1H NMR (400 MHz, CDCl3): d = 0.74 (t, J = 7.6 Hz, 3H),
1.24 (dq, J = 13.6, 7.6 Hz, 1H), 1.31 (s, 3H), 2.02 (dq, J = 13.6, 7.6 Hz, 1H), 2.39–
2.42 (m, 2H), 2.56–2.59 (m, 2H), 4.65 (d, J = 6.0 Hz, 1H), 6.48 (d, J = 6.2 Hz, 1H)
ppm. 13C NMR (100 MHz, DEPT, CDCl3): d = 10.3 (CH3), 25.1 (CH2), 28.2 (CH3),
32.1 (CH2), 33.3 (CH2), 34.4 (C), 114.1 (CH), 119.5 (C), 138.7 (CH), 178.9 (C),
204.2 (C) ppm. MS (EI): m/z 178 [M+]. HRMS: calcd: 178.09938, found:
178.09935.
3. Conclusion
In summary, we have demonstrated that monomeric cyclopen-
tadienone complexes of type 1 are suitable catalysts for regio-
selective additions of carboxylic acids or cyclic 1,3-dicarbonyl
compounds to various terminal propargyl alcohols. The reaction
mechanisms may involve the formation of neutral vinylidene or
allenylidene species. The transformation of internal aromatic prop-
argyl alcohols proceeds by different substrate-dependent path-
Compound 5d (C15H14O2): 1H NMR (400 MHz, CDCl3): d = 1.77 (s, 3H), 2.35–2.40
(m, 2H), 2.60–2.64 (m, 2H), 4.98 (d, J = 6.1 Hz, 1H), 6.57 (d, J = 6.1 Hz, 1H), 7.10–
7.51 (m, 5H) ppm. 13C NMR (100 MHz, DEPT, CDCl3): d = 25.1 (CH2), 26.2 (CH3),
33.3 (CH2), 36.7 (C), 114.9 (CH), 121.0 (C), 126.4 (CH), 127.0 (CH), 128.2 (CH),
137.4 (CH), 146.5 (C), 177.1 (C), 203.7 (C) ppm. MS (EI): m/z 226 [M+]. HRMS:
calcd: 226.09938, found: 226.09961.
Compound 5f (C14H12O2): 1H NMR (400 MHz, CDCl3): d = 2.36–2.40 (m, 2H),

6634
S. Berger, E. Haak / Tetrahedron Letters 51 (2010) 6630–6634
2.59–2.68 (m, 2H), 4.30 (s br, 1H), 5.15 (dd, J = 6.4, 1.0 Hz, 1H), 6.63 (d,
J = 6.4 Hz, 1H), 7.15–7.43 (m, 5H) ppm. 13C NMR (100 MHz, DEPT, CDCl3):
d = 25.4 (CH2), 32.9 (CH2), 34.5 (CH), 108.6 (CH), 117.3 (C), 126.4 (CH), 128.0
(CH), 128.4 (CH), 139.3 (CH), 142.8 (C), 178.1 (C), 203.0 (C) ppm. MS (EI): m/z
212 [M+]. HRMS: calcd: 212.08373, found: 212.08379.
199.3 (C) ppm. MS (EI): m/z 246 [M+]. HRMS: calcd: 246.16198, found:
246.16172.
Compound 5o (C15H14O3): 1H NMR (400 MHz, CDCl3): d = 0.82 (t, J = 7.6 Hz, 3H),
1.26 (dq, J = 13.6, 7.6 Hz, 1H), 1.52 (s, 3H), 2.44 (dq, J = 13.6, 7.6 Hz, 1H), 4.77 (d,
J = 6.0 Hz, 1H), 6.63 (d, J = 6.0 Hz, 1H), 7.25–7.29 (m, 2H), 7.51 (t, J = 7.8 Hz, 1H),
7.74 (d, J = 8.0 Hz, 1H) ppm. 13C NMR (100 MHz, DEPT, CDCl3): d = 10.6 (CH3),
29.2 (CH3), 32.4 (CH2), 34.8 (C), 105.6 (C), 114.2 (CH), 114.3 (C), 116.3 (CH),
122.9 (CH), 123.8 (CH), 131.7 (CH), 137.1 (CH), 152.5 (C), 156.6 (C), 160.9 (C)
ppm. MS (EI): m/z 242 [M+]. HRMS: calcd: 242.09429, found: 242.09422.
Compound 5r (C19H14O3): 1H NMR (400 MHz, CDCl3): d = 2.01 (t, J = 1.2 Hz, 3H),
4.43 (dq, J = 4.5, 1.2 Hz, 1H), 5.00 (dq, J = 4.5, 1.1 Hz, 1H), 7.14 (t, J = 7.1 Hz, 1H),
7.21–7.29 (m, 6H), 7.46 (t, J = 7.4 Hz, 1H), 7.79 (d, J = 7.9 Hz, 1H) ppm. 13C NMR
(100 MHz, DEPT, CDCl3): d = 18.6 (CH3), 36.5 (CH), 103.4 (C), 103.9 (CH), 114.5
(C), 116.7 (CH), 122.7 (CH), 124.0 (CH), 127.0 (CH), 128.2 (CH), 128.5 (CH),
131.8 (CH), 144.2 (C), 145.9 (C), 152.7 (C), 155.9 (C), 161.6 (C) ppm. MS (EI): m/
z 290 [M+]. HRMS: calcd: 290.09429, found: 290.09431.
Compound 5i (C14H18O2): 1H NMR (600 MHz, CDCl3): d = 1.27–1.35 (m, 1H),
1.42–1.49 (m, 5H), 1.60–1.64 (m, 2H), 1.92 (quint., J = 6.6 Hz, 2H), 2.34 (t,
J = 6.6 Hz, 2H), 2.38 (t, J = 6.6 Hz, 2H), 2.53–2.58 (m, 2H), 5.43 (d, J = 6.3 Hz, 1H),
6.23 (d, J = 6.3 Hz, 1H) ppm. 13C NMR (125 MHz, DEPT, CDCl3): d = 20.4 (CH2),
20.8 (CH2), 25.3 (CH2), 28.5 (CH2), 33.4 (C), 35.3 (CH2), 39.5 (CH2), 110.8 (CH),
117.6 (C), 135.0 (CH), 166.8 (C), 198.9 (C) ppm. MS (EI): m/z 218 [M+]. HRMS:
calcd: 218.13068, found: 218.13060.
Compound 5n (C16H22O2): 1H NMR (600 MHz, CDCl3): d = 1.04 (s, 6H), 1.27–
1.33 (m, 1H), 1.42–1.49 (m, 5H), 1.61–1.64 (m, 2H), 2.20 (s, 2H), 2.24 (s, 2H),
2.53–2.58 (m, 2H), 5.43 (d, J = 6.6 Hz, 1H), 6.23 (d, J = 6.6 Hz, 1H) ppm. 13C NMR
(125 MHz, DEPT, CDCl3): d = 20.4 (CH2), 20.7 (CH2), 25.3 (CH2), 27.9 (CH3), 31.4
(C), 33.3 (C), 35.2 (CH2), 42.0 (CH2), 110.7 (CH), 116.3 (C), 135.1 (CH), 165.6 (C),