Intermolecular Morita-Baylis-Hillman reactions using dicobalthexacarbonyl complexed acetylenic acetals

Article abstract of DOI:10.1016/j.tetlet.2010.12.096

An intermolecular Morita-Baylis-Hillman (MBH) reaction using dicobalthexacarbonyl complexed acetylenic acetals as the electrophile is reported. Employing BF₃-OEt₂ as the Lewis acid with a sulfide as the Lewis base MBH adducts were ob

Full text of DOI:10.1016/j.tetlet.2010.12.096

Tetrahedron Letters 52 (2011) 1090–1092
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Intermolecular Morita–Baylis–Hillman reactions using dicobalthexacarbonyl
complexed acetylenic acetals
⇑
Marie E. Krafft , Mark J. Campbell, Sean Kerrigan, John W. Cran
Department of Chemistry and Biochemistry, The Florida State University, Tallahassee, FL 32306-3006, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 30 June 2010
Revised 16 December 2010
Accepted 20 December 2010
Available online 30 December 2010
An intermolecular Morita–Baylis–Hillman (MBH) reaction using dicobalthexacarbonyl complexed acety-
lenic acetals as the electrophile is reported. Employing BF3–OEt2 as the Lewis acid with a sulfide as the
Lewis base MBH adducts were obtained.
Ó 2011 Elsevier Ltd. All rights reserved.
Key words:
Nicholas reaction
C–C bond formation
Lewis acid
Morita–Baylis–Hillman
The Morita–Baylis–Hillman (MBH) reaction is a carbon–carbon
bond forming reaction that exhibits atom economy with genera-
tion of functional groups.1 In the reaction, an activated alkene is
coupled with a carbon electrophile using a nucleophilic catalyst
(Eq. (1)).2 Tertiary amines, trialkylphosphines, sulfides, and Lewis
acids3 have been used to mediate the reaction. The intermolecular
reaction has been developed to accommodate a number of sp2-
hybridized electrophiles including alpha-keto esters, aldehydes,
1,2-diketones, arenes, and vinyl sulfones.2 Activated alkenes used
in the MBH reaction include acrylates, vinyl ketones, sulfones, ni-
triles, sulfoxides, phosphonates, acrolein, thioacrylates, and allenic
esters.2
bond forming process. The use of transition metal complexed re-
agents as electrophiles in the MBH reaction is not common,4 and
dicobalthexacarbonyl complexed acetylenic acetals appeared to
be ideal candidates for the electrophilic partner in the Morita–
Baylis–Hillman reaction due to their known reactivity under acidic
reaction conditions. Reaction of dicobalthexacarbonyl complexed
alkynes bearing an appropriate leaving group at the propargylic
position undergo reaction with Lewis acids to generate stabilized
cationic intermediates known as Nicholas cations (Eq. (2)), which
have been shown to react with a variety of nucleophiles including
hydrides, amines, azides, fluorides, mercaptans, enols, and
alkenes.5
R
O
R
2
2
LG
3
R
1
Lewis
acid
R
OC
OC
1
R
R
Nucleophilic
3
OEt
H
OH
O
CO
CO
Organocatalyst
OC
Co Co
Co Co
CO
CO
OC
OEt
O
CO CO
CO CO
ð1Þ
ð2Þ
LG=leaving group
(OC) Co
6
2
R
3
Nucleophilic Catalyst: DABCO, r.t., 7d, 76% (Baylis-Hillman)1a
Cy3P, 130 °C, 2h, 23% (Morita)1b
R
1
R
2
Dicobalthexacarbonyl complexed acetylenic acetals have not
been reported as electrophilic partners in the MBH reaction and
we herein report their successful application in the carbon–carbon
Commonly used Lewis acids in the MBH reaction include TiCl4
and BF3–OEt2.3 In conjunction with sulfides as the nucleophilic cat-
alyst, TiCl4 has also been used. However, chlorinated side products
are readily generated.3b,c In both MBH and Nicholas reactions, BF3–
OEt2 has been used as a Lewis acid. The Goodman group used BF3–
OEt2 in conjunction with tetrahydrothiophene to promote an
⇑
Corresponding author.
E-mail address: mek@chem.fsu.edu (M.E. Krafft).
0040-4039/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2010.12.096

M. E. Krafft et al. / Tetrahedron Letters 52 (2011) 1090–1092
1091
intermolecular MBH reaction between aldehydes and activated al-
1i) tetrahydrothiophene
(1.2 equiv),
kenes.3d Kataoka et al. developed a Lewis-Acid mediated MBH
R
O
R
1
OEt
EtO
reaction using a sulfide as the mediator.3e
BF -OEt (2.5 equiv)
3
2
O
EtO
CH Cl , 0°C
2
2
ð5Þ
Our initial plan was to develop an intermolecular MBH reaction
between an enone and a dicobalthexacarbonyl complexed alkyne
bearing a leaving group at the propargylic position. We chose
BF3–OEt2 as the Lewis acid since it is common to both the MBH
and the Nicholas reaction.3d–f,6 Initial optimization studies using
Nicholas cations of dicobalthexacarbonyl complexed propargyl
ethers and different Lewis acids such as TiCl4 or BF3–OEt2 were
met with limited success (Eq. (3)).
Co (CO)
2
6
R
1
ii) NEt (3.0 equiv)
3
2
R
CH Cl , 0°C
2
(2 equiv)
(1 equiv)
2) decomplexation
OR
O
Table 1
1) Lewis acid, Lewis base
(CO) Co
6
2
Entry
1
R
MBH product
OEt
% yield (2 steps)
2) Decomplexation
O
R
ð3Þ
O
Me
1
54a
Me
R
2
3
4
5
Et
Pr
Ph
2
3
4
5
61b
54b
65b
61b
R
Acetals have previously been utilized in both MBH reactions
and reactions of dicobalthexacarbonyl complexed alkynes there-
fore they were selected as the electrophilic partner. Increased acti-
vation of the propargylic carbon by the use of an acetal in place of
an ether successfully led to MBH coupling products (Eq. (4)).3f
4-NO2-Ph
OEt
OEt
O
O
6
Me
6
71a
Et
R
R
7
8
9
Et
Pr
Ph
7
8
9
66b
61b
58b
O
S
OEt
EtO
EtO
(OC) Co
O
(1.2 equiv)
1)
10
Me
10
56b
BF3-OEt2 (2.5 equiv)
CH2Cl2, 0 °C
Ph
Co (CO)
2
6
6
2
ð4Þ
11
12
Et
Pr
11
12
47b
54b
R
R
2)
NEt3 (3.0 equiv)
CH2Cl2, 0 °C
a
(2 equiv)
(1 equiv)
(1 equiv)
(1 equiv)
(2 equiv)
(2 equiv)
60-80%
<10%
Decomplexation with NMO.
Decomplexation with CAN.
b
30-35%
Reactions performed with tetrahydrothiophene as the nucleophile
and BF3–OEt2 were the most promising. In the optimization process,
it was found that a 2:1 excess of the dicobalthexacarbonyl com-
plexed acetylenic acetal to the activated alkene achieved highest
yields(Eq. (4)). Withanequalratioofthedicobalthexacarbonylcom-
plexed acetylenic acetal to activated alkene or if an excess of
activated alkene was used, the yields decreased. A series of intermo-
lecular MBH adducts was synthesized (Table 1, Eq. (5)) using com-
mercially available propargylic acetals or propargylic acetals
synthesized under Sonogashira coupling conditions.7 Use of propiol-
aldehyde diethyl acetals resulted in low isolated yields of
anticipated coupling product in addition to significant starting
material decomposition under the Lewis acidic conditions.
Other Lewis acids such as BaCl2, SmI2, AlCl3, AgNO3, and SnCl4
were screened and resulted in little or no formation of the desired
MBH product. Reaction of the uncomplexed 2-butynal-diethylacetal
with pent-1-ene-3-one under the same reaction conditions yielded
only 50% of the MBH adduct 6. The reaction produced more
byproducts thus reinforcing the effectiveness of the complexed al-
kyne. Uncomplexed 2-octynal underwent reaction with pent-1-
ene-3-one under the same reaction conditions to give alkyne 13
in 75% yield as the free alcohol rather than the propargylic ether.
These conditions give rise to the coupling product in much shorter
reaction time than the corresponding base-catalyzed process.8
Initial carbon–carbon bond formation leaves the cobalt complex
coordinated to the alkyne. Oxidation using either N-methylmor-
pholine-N-oxide (NMO) or ceric ammonium nitrate (CAN) liberates
the free alkyne. While the metal can be decomplexed directly in
the initial reaction flask, yields were higher when filtration of the
reaction through CeliteÒ to remove some of the cobalt residues
(OC) Co
6
2
O
R
OH
O
X
Et
X=OEt, OAc
C H
n=1,2
5
11
13
14
was conducted after the Lewis acid-mediated MBH reaction but
prior to decomplexation.9
Alternative activated alkenes including 4-nitrophenyl vinyl
ketone and thioacrylic acid-S-ethyl ester did not work under Lewis
acidic conditions. In addition, beta-substituted activated alkenes
such as 3-penten-2-one and cyclohexenone were inert to the reac-
tion conditions. Attempts to develop an intramolecular reaction
using enone 14 were not successful. With either an acetate or
alkoxy leaving group, there was either no reaction or decomposi-
tion of starting material under Lewis acidic or phosphine-mediated
conditions.
In summary, an intermolecular MBH reaction with activated
alkenes has been developed using the dicobalthexacarbonyl com-
plexed acetylenic acetal as the electrophile. The use of cationic
intermediates stabilized by an adjacent dicobalthexacarbonyl com-
plexed alkyne represents an alternative class of electrophiles in the
MBH reaction.
Acknowledgments
This work was funded by the National Science Foundation and
the MDS Research Foundation (Tallahassee, FL).

1092
M. E. Krafft et al. / Tetrahedron Letters 52 (2011) 1090–1092
was evaporated.
References and notes
A 1H NMR spectrum was recorded of the reaction mixture. The NMR sample was
prepared by filtration of the mixture through charcoal and CeliteÒ. Without
column chromatography, the mixture was subjected to cobalt decomplexation
conditions. To the reaction mixture dissolved in 2 mL of THF and 1 mL of
acetone, ceric ammonium nitrate was added slowly until the red color
characteristic of dicobalthexacarbonyl complexes no longer appeared by TLC.
The mixture was filtered through a plug of silica gel and concentrated by
evaporation. Column chromatography on silica gel provided enone 4 as a yellow
1. (a) Baylis, A. B.; Hillman, M. E. D. German Patent 2155113, 1972; Chem. Abstr.
1972, 77, 3417q.; (b) Morita, K.; Suzuki, Z. L.; Hirose, H. Bull. Chem. Soc. Jpn 1968,
41, 2815.
2. For a general review of Baylis–Hillman reactions see: Basavaiah, D.; Rao, A. J.;
Satyanarayana, T. Chem. Rev. 2003, 103, 811–891; Ma, G.-N.; Jiang, J.-J.; Shi, M.;
Wei, Y. Chem. Commun. 2009, 5496; Krafft, M. E.; Seibert, K. A.; Haxell, T. F. N.
Synlett 2010, 2583.
3. (a) Kataoka, T.; Iwama, T.; Tsujiyama, S.; Iwamura, T.; Watanabe, S. Tetrahedron
1998, 54, 11813; (b) Li, G.; Gao, J.; Han-Xun, W.; Enright, M. Org. Lett. 2000, 2,
617; (c) Shi, M.; Feng, Y. S. J. Org. Chem. 2001, 66, 406; (d) Walsh, L. M.; Winn, C.
L.; Goodman, J. M. Tetrahedron Lett. 2002, 43, 8219; (e) Kataoka, T.; Iwama, T.;
Tsujiyama, S. Tetrahedron 1998, 54, 11813; (f) Kinoshita, H.; Osamura, T.;
Kinoshita, S.; Iwamura, T.; Watanabe, S.; Kataoka, T.; Tanabe, G.; Muraoka, O. J.
Org. Chem. 2003, 68, 7532; (g) Sohtome, Y.; Takemura, N.; Takagi, R.; Hashimoto,
Y.; Nagasawa, K. Tetrahedron 2008, 64, 9423.
4. (a) Aggarwal, V. K.; Mereu, A.; Tarver, G. J.; McCague, R. J. Org. Chem. 1998, 63,
7183; (b) Jellerichs, B. G.; Kong, J. R.; Krische, M. J. J. Am. Chem. Soc. 2003, 125,
7758.
5. (a) Teobald, B. J. Tetrahedron 2002, 58, 4133–4170; (b) Nicholas, K. M. Acc. Chem.
Res. 1987, 20, 207–214; (c) Bromfield, K. M.; Graden, H.; Ljungdahl, N.; Kann, N.
Dalton Trans. 2009, 5051; (d) Diaz, D. D.; Betancort, J. M.; Martin, V. S. Synlett
2007, 343.
6. (a) Krafft, M. E.; Cheung, Y. Y.; Wright, C.; Cali, R. J. Org. Chem. 1996, 61, 3912–
3915; (b) Tyrrell, E.; Claridge, S.; Davis, R.; Lebel, J.; Berge, J. Synlett 1995, 714–
716; (c) Ganesh, P.; Nicholas, K. M. J. Org. Chem. 1997, 62, 1737–1747.
7. (a) Cacchi, S.; Fabrizi, G.; Marinelli, F.; Moro, L.; Pace, P. Tetrahedron 1996, 52,
10225; (b) Lemhadri, M.; Doucet, H.; Santelli, M. Tetrahedron 2005, 61, 9839.
8. Krishna, P. R.; Sekhar, E. R.; Kannan, V. Tetrahedron Lett. 2003, 44, 4973.
oil (0.094 g, 65% over
2 d 7.46 (m, 2H,
steps). 1H NMR 300 MHz (CDCl3)
aromatic), 7.32 (m, 3H, aromatic), 6.48 (br s, 1H, C@CHH), 6.30 (br s, 1H,
C@CHH), 5.35 (br s, 1H, CH3CH2OCH), 3.85 (ABq, JAB = 8.8, J = 6.8, 1H,
CH3CHHOCH), 3.60 (ABq, JAB = 8.8, J = 6.8, CH3CHHOCH), 2.41 (s, 3H, CH3CO),
1.26 (t, J = 6.8, 3H, CH3CH2OCH); 13C NMR 75 MHz (CDCl3) d 201.7, 150.7, 136.1,
132.8, 132.6, 131.1, 126.9, 91.1, 90.7, 71.1, 69.3, 26.9, 19.4. IR (cmꢁ1): 3445,
2977, 2198, 1682, 1080, 758. MS [FAB, m/z (rel intensity)]: 251 (M++1), 241, 221.
4-Ethoxy-3methylene-6-(4-nitro-phenyl)-hex-5-yn-2-one, 5. 1H NMR 300 MHz
(CDCl3)
d 8.18 (m, 2H, aromatic), 7.59 (m, 2H, aromatic), 6.44 (br s, 1H,
C@CHH), 6.32 (br s, 1H, C@CHH), 5.37 (br s, 1H, CH3CH2OCH), 3.85 (ABq,
JAB = 9.0, J = 6.8, 1H, CH3CHHOCH), 3.60 (ABq, JAB = 9.0, J = 6.8, CH3CHHOCH),
2.44 (s, 3H, CH3CO), 1.28 (t, J = 7.2, 3H, CH3CH2OCH).
5-Ethoxy-4-methylene-oct-6-yn-3-one, 6. 1H NMR 300 MHz (CDCl3) d 6.28 (br s,
1H, C@CHH), 6.18 (br s, 1H, C@CHH), 5.07 (br s, 1H, CH3CH2OCH), 3.75 (ABq,
JAB = 9.0, J = 7.2, 1H, CH3CHHOCH), 3.49 (ABq, JAB = 9.0, J = 7.2, 1H, CH3CHHOCH),
2.79 (ABq, JAB = 13.0, J = 3.0, 1H, CH3CHHCO), 2.73 (ABq, JAB = 13.0, J = 3.0, 1H,
CH3CHHCO), 1.87 (d, J = 2.7, 3H, CH3C„C), 1.20 (t, J = 7.2, 3H, CH3CH2OCH), 1.11
(t, J = 7.2, 3H, CH3CH2CO). 13C NMR 75 MHz (CDCl3) d 201.97, 150.97, 130.76,
87.05, 81.50, 70.77, 68.90, 30.65, 30.63, 19.3, 8.08. IR (cmꢁ1): 3446, 2977, 2228,
1681, 1081. MS [EI, m/z (rel intensity)]: 179, 165, 151, 123, 97.
5-Ethoxy-4-methylene-non-6-yn-3-one, 7. 1H NMR 300 MHz (CDCl3) d 6.28 (br s,
1H, C@CHH), 6.16 (br s, 1H, C@CHH), 5.11 (br s, 1H, CH3CH2OCH), 3.75 (ABq,
JAB = 9.0, J = 6.8, 1H, CH3CHHOCH), 3.50 (ABq, JAB = 9.0, J = 6.8, 1H, CH3CHHOCH),
2.97 (ABq, JAB = 13.0, J = 6.8, 1H, CH3CHHCO), 2.73 (ABq, JAB = 13.0, J = 6.8, 1H,
CH3CHHCO), 2.27 (qd, J = 7.8, 2.4, 2H, CH3CH2C„C), 1.21 (t, J = 6.6, 3H,
CH3CH2OCH), 1.15 (t, J = 6.6, 3H, CH3CH2C„C), 1.12 (t, J = 8.0, 3H, CH3CH2CO).
13C NMR 75 MHz (CDCl3) d 205.03, 150.74, 129.35, 93.32, 81.48, 71.17, 68.82,
36.02, 19.39, 18.10, 16.76, 12.39. IR (cmꢁ1): 3582, 2977, 2229, 1688, 1083. MS
[CI, m/z (rel intensity)]: 195 (M++1), 149, 111.
9. 4-Ethoxy-3-methylene-hept-5-yn-2-one, 1. To
a
stirred solution of
dicobalthexacarbonyl complexed 2-butyn-1-al diethyl acetal (0.493 g,
1.15 mmol) in 2 mL of CH2Cl2 at 0 °C were added tetrahydrothiophene
(0.062 mL, 0.696 mmol) and methyl vinyl ketone (0.048 mL, 0.57 mmol). After
stirring for 10 min, freshly distilled BF3–OEt2 (0.184 mL, 1.45 mmol) was added
over 5 min and the reaction was followed by TLC. Upon consumption of the
enone starting material, the reaction was quenched with NEt3 (0.243 mL,
1.75 mmol). After warming to room temperature, the mixture was washed
successively with aqueous HCl (1 M) and saturated NaHCO3 (aq). The mixture
was dried over Na2SO4 and the solvent was evaporated.
Without column chromatography, the mixture was subjected to cobalt
decomplexation conditions. To the reaction mixture dissolved in 3 mL of
CH2Cl2, NMOꢀH2O was added slowly until the red color characteristic of
dicobalthexacarbonyl complexes no longer appeared by TLC. The mixture was
filtered through a plug of silica gel and concentrated by evaporation. Column
chromatography on silica gel provided enone 1 as a yellow oil (0.052 g, 54% yield
over 2 steps). 1H NMR 300 MHz (CDCl3) d 6.32 (br s, 1H, C@CHH), 6.20 (br s, 1H,
C@CHH), 5.06 (br s, 1H, CH3CH2OCH), 3.76 (ABq, JAB = 9.0, J = 6.2, 1H,
CH3CHHOCH), 3.49 (ABq, JAB = 9.0, J = 6.2, 1H, CH3CHHOCH), 2.38 (s, 3H,
CH3CO), 1.87 (d, J = 2.4, 3H, CH3C„C), 1.21 (t, J = 6.6, 3H, CH3CH2OCH); 13C
(CDCl3) d 201.2, 151.1, 130.6, 87.2, 80.8, 70.9, 68.9, 30.6, 19.4, 7.9. IR (cmꢁ1):
3434, 2976, 2229, 1651, 1079. MS [CI, m/z (rel intensity)]: 167 (M++1), 151, 137,
121, 97.
5-Ethoxy-4-methylene-dec-6-yn-3-one, 8. 1H NMR 300 MHz (CDCl3) d 6.29 (br s,
1H, C@CHH), 6.18 (br s, 1H, C@CHH), 5.13 (br s, 1H, CH3CH2OCH), 3.77 (ABq,
JAB = 9.1, J = 6.8, 1H, CH3CHHOCH), 3.50 (ABq, JAB = 9.1, J = 6.8, 1H, CH3CHHOCH),
2.78 (ABq, JAB = 13.0, J = 6.8, 1H, CH3CHHCO), 2.72 (ABq, JAB = 13.0, J = 6.8, 1H,
CH3CHHCO).
5-Ethoxy-4-methylene-7-phenyl-hept-6-yn-3-one, 9. 1H NMR 300 MHz (CDCl3) d
7.46 (m, 2H, aromatic), 7.32 (m, 3H, aromatic), 6.38 (br s, 1H, C@CHH), 6.25 (br s,
1H, C@CHH), 5.37, (br s, 1H, CH3CH2OCH), 3.86 (ABq, JAB = 8.9, J = 6.8, 1H,
CH3CHHOCH), 3.62 (ABq, JAB = 8.9, J = 6.8, 1H, CH3CHHOCH), 2.83 (ABq,
JAB = 17.2, J = 7.8, 1H, CH3CHHCO), 2.75 (ABq, JAB = 17.2, J = 7.8, 1H,
CH3CHHCO), 1.26 (t, J = 6.8, 3H, CH3CH2OCH), 1.15 (t, J = 7.8, 3H, CH3CH2CO).
13C NMR 75 MHz (CDCl3) d 204.90, 150.07, 135.95, 132.77, 132.58, 129.71,
126.88, 91.16, 90.71, 71.70, 69.45, 35.91, 19.14, 12.69, 5.59. IR (cmꢁ1): 3584,
2976, 2223, 1681, 1089, 758. MS [EI, m/z (rel intensity): 241 (M++1)], 213, 198,
185, 157, 139, 111.
3-Ethoxy-2-methylene-1-phenyl-hex-4-yn-1-one, 10. 1H NMR 300 MHz (CDCl3) d
7.84 (m, 2H, aromatic), 7.56 (m, 1H, aromatic), 7.47 (m, 2H, aromatic), 6.35 (br s,
1H, C@CHH), 5.73 (br s, 1H, C@CHH), 5.29 (br s, 1H, CH3CH2OCH), 3.82 (ABq,
JAB = 9.0, J = 6.4, 1H, CH3CHHOCH), 3.55 (ABq, JAB = 9.0, J = 6.4, 1H, CH3CHHOCH),
1.89 (d, J = 2.4, 3H, CH3C„C), 1.20 (t, J = 7.2, 3H, CH3CH2OCH). 13C NMR 75 MHz
(CDCl3) d 200.32, 150.31, 144.82, 136.87, 133.96, 132.54, 129.46, 88.22, 81.52,
72.42, 69.11, 19.33, 7.97. IR (cmꢁ1): 3390, 2928, 2357, 1652, 1078, 757. MS [CI,
m/z (rel intensity)]: 229 (M++1), 183, 105.
4-Ethoxy-3-methylene-oct-5-yne-2-one, 2. 1H NMR 300 MHz (CDCl3) d 6.33 (br s,
1H, C@CHH), 6.20 (br s, 1H, C@CHH), 5.09 (br s, 1H, CH3CH2OCH), 3.75 (ABq,
JAB = 9.0, J = 6.1, 1H, CH3CHHOCH), 3.50 (ABq, JAB = 9.0, J = 6.1, 1H, CH3CHHOCH),
2.25 (qd, J = 7.2, 1.8, 2H, CH3CH2C„C), 1.21 (t, J = 6.6, 3H, CH3CH2OCH), 1.15 (t,
J = 7.2, 3H, CH3CH2C„C). 13C NMR 75 MHz (CDCl3) d 201.97, 150.96, 130.76,
93.39, 80.84, 70.81, 68.88, 30.73, 19.38, 18.03, 10.81. IR (cmꢁ1): 3583, 2977,
2229, 1682, 1081(cmꢁ1) MS [CI (rel intensity)]: 181 (M++1), 135, 85.
4-Ethoxy-3-methylene-non-5-yn-2-one, 3. 1H NMR 300 MHz (CDCl3) d 6.32 (br s,
1H, C@CHH), 6.19 (br s, 1H, C@CHH), 5.09 (br s, 1H, CH3CH2OCH), 3.79 (ABq,
JAB = 9.0, J = 7.0, 1H, CH3CHHOCH), 3.53 (ABq, JAB = 9.0, J = 7.0, 1H, CH3CHHOCH),
2.41 (s, 3H, CH3CO), 2.22 (td, J = 7.2, 1.8, 2H, CH3CH2CH2C „C), 1.55 (qt, J = 7.2,
7.2, 2H, CH3CH2CH2C„C), 1.22 (t, J = 7.2, 3H, CH3CH3OCH), 0.99 (t, J = 7.2, 3H,
CH3CH2CH2C„C). 13C NMR 75 MHz (CDCl3) d 201.97, 151.19, 130.58, 91.88,
81.66, 70.90, 68.86, 30.69, 26.33, 25.11, 19.36, 17.70. IR (cmꢁ1): 3502, 2969,
2228, 1688, 1080. MS [CI, m/z (rel intensity)]: 195 (M++1), 149.
3-Ethoxy-2-methylene-1-phenyl-hept-4-yn-1-one, 11. 1H NMR 300 MHz (CDCl3) d
7.83 (m, 2H, aromatic), 7.56 (m, 2H, aromatic), 7.47 (m, 2H, aromatic), 6.32 (br s,
1H, C@CHH), 5.73 (br s, 1H, C@CHH), 5.27 (br s, 1H, CH3CH2OCH), 3.80 (ABq,
JAB = 9.0, J = 6.8, 1H, CH3CHHOCH), 3.57 (ABq, JAB = 9.0, J = 6.8, 1H, CH3CHHOCH),
2.26 (qd, J = 7.8, 2.4, 2H, CH3CH2C„C), 1.23 (t, J = 7.2, 3H, CH3CH2OCH), 1.18 (t,
J = 7.2, 3H, CH3CH2C„C). 13C NMR 75 MHz (CDCl3) d 200.56, 150.36, 141.81,
136.89, 133.99, 132.55, 129.19, 94.10, 81.50, 72.00, 69.09, 19.41, 18.17, 16.84. IR
(cmꢁ1): 2977, 2224, 1682, 1084, 757. MS [FAB, m/z (rel intensity)]: 265.
(M++Na], 242.0.
4-Ethoxy-3-methylene-6-phenyl-hex-5-yn-2-one, 4. To
a stirred solution of
dicobalthexacarbonyl complexed phenylpropargyl aldehyde diethyl acetal
(0.929 g, 1.90 mmol) in 3 mL of CH2Cl2 at 0 °C were added
tetrahydrothiophene (0.064 mL, 0.760 mmol) and methyl vinyl ketone
(0.053 mL, 0.630 mmol). After stirring for 10 min, freshly distilled BF3–OEt2
(0.253 mL, 2.01 mmol) was added over 5 min and the reaction was followed by
TLC. Upon consumption of the enone starting material, the reaction was
quenched with NEt3 (0.348 mL, 2.50 mmol). After warming to room
temperature, the mixture was washed successively with aqueous HCl (1 M)
and saturated NaHCO3 (aq). The mixture was dried over Na2SO4 and the solvent
3-Ethoxy-2-methylene-1-phenyl-oct-4-yn-1-one, 12. 1H NMR 300 MHz (CDCl3) d
7.86 (m, 2H, aromatic), 7.56 (m, 1H, aromatic), 7.45 (m, 2H, aromatic), 6.33 (br s,
1H, C@CHH), 5.71 (br s, 1H, C@CHH), 5.31 (br s, 1H, CH3CH2OCH), 3.81 (ABq,
JAB = 9.0, J = 6.0, 1H, CH3CHHOCH), 3.57 (ABq, JAB = 9.0, J = 6.0, 1H, CH3CHHOCH),
2.25 (td, J = 7.2, 1.8, 3H, CH3CH2CH2C„C), 1.55 (tq, J = 7.2, 7.2, 2H,
CH3CH2CH2C„C),
1.24
(t,
J = 7.2,
CH3CH2OCH),
0.99
(t,
J = 7.2,
CH3CH2CH2C„C). IR (cmꢁ1): 3582, 2965, 2203, 1665, 1087, 756. MS [CI, m/z
(rel intensity)]: 255 (M++1), 227, 105, 77.