Ethenolate transfer reactions: A facile synthesis of vinyl esters

Article abstract of DOI:10.1002/hlca.201300396

A simple and efficient metal-free ethenolate transfer reaction has been elaborated in moderate-to-high yields from vinyl acetate. This reaction was accomplished by generation of potassium ethenolate, which was then reacted with homo and mixed anhydrides of aliphatic, aryl and heteroaryl acids, to yield the corresponding vinyl esters. The utility of thus generated vinyl esters was then probed by carrying out intramolecular Heck reactions to give isobenzofuran-1(3H)-one derivatives in excellent yields. Copyright

Full text of DOI:10.1002/hlca.201300396

Helvetica Chimica Acta – Vol. 97 (2014)
1115
Ethenolate Transfer Reactions: A Facile Synthesis of Vinyl Esters
by Srinivasan Kaliyaperumal Appayea)b), Satish Pandurang Nikumbha), Rajeshwar Reddy
Govindapura), Shyamapada Banerjeea), Dinesh S. Bhaleraoc), and Unniaran K. Syam Kumar*c)
a) Technology Development Centre, Custom Pharmaceutical Services, Dr. Reddyꢀs Laboratories Ltd.,
Miyapur, Hyderabad, Pin 500 049, India
b) Chemistry Division, Institute of Science and Technology, Jawaharlal Nehru Technological University,
Hyderabad, Pin 500 072, India
c) Integrated Product Development, Innovation Plaza, Dr. Reddyꢀs Laboratories Ltd., Bachupalli,
Qutubullapur, R. R. Dist. 500 072, Andhra Pradesh, India (e-mail: syam_kmr@yahoo.com)
A simple and efficient metal-free ethenolate transfer reaction has been elaborated in moderate-to-
high yields from vinyl acetate. This reaction was accomplished by generation of potassium ethenolate,
which was then reacted with homo and mixed anhydrides of aliphatic, aryl and heteroaryl acids, to yield
the corresponding vinyl esters. The utility of thus generated vinyl esters was then probed by carrying out
intramolecular Heck reactions to give isobenzofuran-1(3H)-one derivatives in excellent yields.
Introduction. – Vinyl ethers and vinyl esters are a valuable class of intermediates
and have been widely used in organic synthesis. Particularly, vinyl ethers and vinyl
esters are used in cycloadditions [1], cyclopropanations [2], hydroformylations [3],
metathesis reactions [4], and Claisen rearrangements [5], as well as Heck reactions [6].
Vinyl esters and ethers are also used as substrates for asymmetric hydrolysis and
alcoholysis reactions [7]. Though vinyl ethers and vinyl esters have considerable
potentials in organic synthesis, the apparent difficulty of the preparation of these
intermediates limit their practical applications. Currently, these are obtained, with high
atom economy, from the addition of a carboxylic acid or alcohol to acetylene. However,
the harsh reaction conditions coupled with safety concerns associated with the
explosive nature of acetylene limit commercial manufacture of vinyl ethers and vinyl
esters by this method. Alternatively, vinyl transfer from vinyl acetate to aliphatic,
aromatic, and heteroaromatic alcohols and acids provides a safe and efficient synthesis
of corresponding vinyl ethers and vinyl esters.
There are several reports on the synthesis of aliphatic, aromatic, and heteroar-
omatic vinyl esters. The reaction of divinylmercury with aromatic and aliphatic acids
gave the vinyl esters in good yields, along with metallic mercury [8]. The CuII-catalyzed
esterification of arene carboxylic acids with trimethoxy(vinyl)silane is known to give
the corresponding vinyl arenecarboxylate in good yields in the presence of AgF [9].
Vinyl transfer reactions from vinyl acetate to primary and secondary alcohols, and also
to carboxylic acids have been reported with a catalyst system consisting of 2 mol-% of
[AuCl(PPh3)] and 2 mol-% of AgOAc [10]. The Ir complex ([Ir(cod)Cl]2/P(OMe)3)-
catalyzed transvinylation is also noteworthy [11]. The [(1-acyloxy)alkylidene]penta-
carbonylchromium(0) complex formed in situ by the reaction of tetramethylammonium
ꢀ 2014 Verlag Helvetica Chimica Acta AG, Zꢁrich

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Helvetica Chimica Acta – Vol. 97 (2014)
(1-oxoalkyl)pentacarbonylchromate salts with carboxylic acid halides also afforded
vinyl esters [12]. All these transformations either use expensive or toxic metal
complexes or highly unstable (alkoxy)vinylsilanes.
Results and Discussion. – As a part of our ongoing research on the development of
new synthetic methodologies for natural product synthesis and biologically active
compounds [13], herein we report an efficient and practical synthesis of vinyl esters by
ethenolate transfer reactions.
We assumed that ethenolate can be efficiently generated from vinyl acetate by the
use of a nucleophilic base; this in situ formed ethenolate can further react with esters
and homo or mixed anhydrides to yield the corresponding aliphatic, aromatic, and
heteroaromatic vinyl esters (Scheme 1).
Scheme 1. Synthesis of Ethenyl Esters Starting from Ethenyl Acetate
The ethenolate transfer reaction was initially attempted on methyl 4-methylben-
zoate (1a) using vinyl acetate (¼ethenyl acetate; 3a) as the ethenolate source in various
i
i
organic solvents in the presence of nucleophilic bases such as PrMgBr, PrONa, and
tBuOK, however, no formation of vinyl 4-methylbenzoate (¼ethenyl 4-methylben-
zoate; 4a) was observed under these reaction conditions (Table 1, Entry 1). The
ethenolate transfer reaction was then attempted with homo and mixed anhydrides 1c,
1b and 1d – 1f, respectively, of 4-methylbenzoic acid. The in situ generated potassium
ethenolate, when reacted with acetic 4-methylbenzoic anhydride (1b) in THF, using 1.2
t
equiv. of BuOK as the base, gave the ethenolate-transfer product, i.e., vinyl 4-
methylbenzoate (4a) in 60% yield (Table 1, Entry 2). However, in the same reaction
with the corresponding 4-methylbenzoic anhydride (1c), 4a was isolated only in 41%
t
yield (Table 1, Entry 3). By using 2 equiv. of BuOK, the yield of 4a dropped to 20%
(Table 1, Entry 4).The ethenolate transfer reaction was also carried out with ethyl 4-
methylbenzoyl carbonate (1d), 1H-imidazole-1-carboxylic 4-methylbenzoic anhydride
(1e), and 1-[(4-methylbenzoyl)oxy]-1H-benzotriazole (1f; Table 1, Entries 5 – 7). The
best yield of 4a (70%) was obtained when the reaction was performed on 1d with 3a
(Table 1, Entry 5).
The probable mechanism of the reaction involves the formation of potassium
t
ethenolate (3b) by the reaction of 3a with BuOK (Scheme 2). Subsequently, the so-
formed 3b reacts with 4-methylbenzoic anhydride (1c) to yield the desired product 4a.
The nucleophilic attack of tBuOK on 3a was further established by the characterization
of tert-butyl acetate (5) as by-product in the reaction.

Helvetica Chimica Acta – Vol. 97 (2014)
1117
Table 1. Optimization of the Ethenolate Transfer Reactionsa)
Entry
Starting material
R1
Mol-equiv. of 3a
Yieldb)
1
2
3
4
5
6
7
1a
1b
1c
1c
1d
1e
1f
Me
1.2
1.2
1.2
2.0
1.2
1.2
1.2
–
MeC¼O
60
41
20
70
15
25
4-MeꢀC6H4ꢀC¼O
4-MeꢀC6H4ꢀC¼O
COOEt
(1H-Imidazol-1-yl)carbonyl
1H-Benzotriazol-1-yl
a
) Reactions were carried out with 1.2 equiv. of BuOK in THF at ꢀ 408. b) Yield of isolated 4a [%].
t
Scheme 2. Postulated Mechanism of the Ethenyl 4-Methylbenzoate Formation
To evaluate the scope and limitations of this versatile metal-free ethenolate transfer
reaction, a series of homo and mixed anhydrides of tert-butyl, aryl, and heteroaryl acids
were synthesized as reported in [14], which were then subjected to ethenolate transfer
reaction under the optimized reaction conditions (Table 2, Entries 1 – 16). All these
homo and mixed anhydrides of aliphatic, aryl, and heteroaryl acids underwent
ethenolate transfer reactions smoothly, and the corresponding vinyl esters were
isolated in moderate-to-very-good yields. The ethenolate transfer reactions resulted in
lower yields of the products, when the reactions were carried out in the presence of
residual Et3N or the corresponding Et3NHCl (the base or corresponding HCl salt used
for the anhydride preparation); hence, during the workup of homo and mixed
anhydrides, Et3N and its salts were removed completely. All the vinyl esters obtained by

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Helvetica Chimica Acta – Vol. 97 (2014)
this ethenolate transfer reaction were characterized by IR, 1H- and 13C-NMR, and mass
spectra, and, in few cases, by elemental analysis. All the vinyl ether transfer reactions
were carried out at ꢀ 30 to ꢀ 408, and the reactions were quenched with NH4Cl
solution below ꢀ 108. The organic layer was separated from aqueous layer well below
108.
The ethenolate transfer reaction exhibits a very good functional-group tolerance.
The electronic effects of the substituent on the aryl ring did not exert any influence on
the reaction conversion. Also mixed anhydrides of 3-nitro, 4-nitro, and 2-bromoben-
zoic acid (2e, 2f, and 2i, resp.), gave higher yields of vinyl esters in comparison to the
corresponding homo anhydrides. The apparent difficulty of the synthesis as well as the
stability of homo anhydrides of 1,3-dimethyl-1H-pyrazole-4-carboxylic acid (2j),
thiophene-2-carboxylic acid (2k), 6-hydroxynaphthalene-1-carboxylic acid (2l), and 1-
benzyl-1H-indole-3-carboxylic acid (2m) prompted us to carry out the ethenolate
transfer on the corresponding mixed anhydrides (Table 2).
The vinyl benzoates 4j and 4q prepared by ethenolate transfer reaction were then
used for the synthesis of 3-methylidene-2-benzofuran-1(3H)-ones 7a and 7b. Thus,
vinyl 2-bromobenzoate (4j) was subjected to an intramolecular Heck reaction using
Table 2. Scope of the Ethenolate Transfer Reactionsa)
Entry 2/2’
R
4
Yield from 2b) Yield from 2’b) M.p. [8]
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
2a/2a’
Ph
4b
4c
4d
4e
4f
4g
4h
4i
60
66
58
43
58
44
70
56
45
–
–
–
–
39
–
55
39
51
58
58
51
72
–
55
44
48
35
38
–
Viscous liquid
Viscous liquid
58 – 608 [15]
Viscous liquid
57 – 598 [16]
75 – 778 [7]
59 – 618 [17]
57 – 598
Viscous liquid
Viscous liquid
Viscous liquid
137 – 1408
2b/2b’ 4-FꢀC6H4
2c/2c’
4-BrꢀC6H4
2d/2d’ 3-F3CꢀC6H4
2e/2e’
2f/2f’
2g/2g’
3-O2NꢀC6H4
4-O2NꢀC6H4
4-MeOꢀC6H4
2h/2h’ 3,4-(MeO)2ꢀC6H3
2i/2i’
2j/2j’
2-BrꢀC6H4
4j
1,3-Dimethyl-1H-pyrazol-5-yl 4k
2k/2k’ Thiophen-2-yl
2l/2l’
2m/2m’ 1-Benzyl-1H-indol-3-yl
2n/2n’ Me3C
4l
6-Hydroxynaphthalen-1-yl
4mc)
4n
Viscous liquid
Viscous liquid
65 – 678
4o
4p
4q
2o/2o’ 2-Br,5-O2NꢀC6H3
42
44
2p
2,5-Br2,4-MeꢀC6H2
–
101 – 1038
a) Reactions were carried out with 1.2 equiv. of tBuOK in THF at ꢀ 408. b) Yield of the isolated product.
c) Also the OH group of 2l reacted with 3a.

Helvetica Chimica Acta – Vol. 97 (2014)
1119
Pd(PPh3)4 in the presence of K2CO3 in toluene to give 3-methylidene-2-benzofuran-
1(3H)-one (7a) in 86% yield, as an off-white solid. Then, 7a was converted to 1H-
t
indene-1,3(2H)-dione (9) by ring opening with BuOK, followed by in situ intra-
molecular cyclization in THF at reflux temperature (Scheme 3). Similarly, vinyl
benzoate 4q was subjected to an intramolecular Heck reaction, and the 5-exo
cyclization product, 6-bromo-5-methyl-3-methylidene-2-benzofuran-1(3H)-one (7b),
was isolated in 83% yield. The intramolecular Heck reaction on 4j and 4q exclusively
gave the preferred 5-exo cyclization products and no 6-endo cyclization products, which
1
was confirmed by recording the H-NMR spectra of the crude mixture after workup.
Scheme 3. Synthetic Applications of Ethenyl 2-Bromobenzoates
Conclusions. – We have developed a highly efficient synthetic method for
generation of ethenolate, which was then used for ethenolate transfer reactions under
metal-free conditions. This process provides a convenient method for vinyl ester
synthesis via transfer of ethenolate from vinyl acetate to homo and mixed anhydrides in
moderate-to-good yields under very mild reaction conditions. The synthetic utility of
the vinyl esters thus obtained was demonstrated by carrying out intramolecular Heck
reactions in good yields. We are currently exploiting the synthetic applications of vinyl
esters for the preparation of indoles and pyrroles, which will be reported in due course.
The authors acknowledge Dr. Vilas H. Dahanukar, Dr. Reddyꢀs Laboratories, for his constant
encouragement, and Dr. Reddyꢀs Laboratories, for providing analytical support.
Experimental Part
General. All reactions were carried out in oven-dried glassware under N2, with magnetic stirring, and
they were monitored by TLC (Merck Al-backed plates pre-coated with silica (0.25 mm, 60 F254),

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Helvetica Chimica Acta – Vol. 97 (2014)
visualization under UV light (254 nm) or developed using a soln. of KMnO4). Purifications were
performed by column chromatography (CC) with silica gel (SiO2; 60 – 120 mesh) purchased from SRL;
elution with hexanes/AcOEt. M.p.: Electrothermal melting-point apparatus; uncorrected. IR Spectra:
PerkinElmer 1650 Fourier Transform spectrometer. NMR Spectra: in CDCl3, CD3OD, or (D6)DMSO
(all with TMS as internal standard) on a Varian Gemini 200 MHz FT and 400 MHz FT spectrometers;
chemical shifts in ppm; and coupling constants (J) in Hz. MS: HP-5989A quadrupole mass spectrometer.
t
Representative Procedure: Synthesis of Ethenyl 4-Methylbenzoate (4a). A suspension of BuOK
(1.0 g, 9.4 mmol) in 10 ml of dry THF was cooled to ꢀ 30 to ꢀ 408. A soln. of ethenyl acetate (3a; 0.81 g,
9.4 mmol) in THF (2 ml) was added to the mixture during 10 – 20 min. The addition rate of 3a was
controlled in such a way that the temp. did not rise above ꢀ 308, and the mixture was further stirred for
30 min at the same temp. A soln. of 4-methylbenzoic anhydride (1c; 2.0 g, 7.8 mmol) in dry THF (4 ml)
was added to the mixture at ꢀ 30 to ꢀ 408, and the mixture was stirred for another 1 – 2 h at the same
temp. The reaction was then quenched with 5% NH4Cl soln. (20 ml) below ꢀ 108, and the mixture was
t
extracted with BuOMe (10 ml). The combined org. layer was washed with H2O (2 ꢁ 20 ml) and brine
(20 ml), dried (Na2SO4; 5 g), and concentrated. The residue was purified by CC (hexane/AcOEt 5 :1) to
afford 0.9 g (70%) of 4a. Viscous liquid [7]. IR (KBr): 1729, 1646. 1H-NMR (400 MHz, CDCl3): 8.00 (d,
J ¼ 8.3, 2 H); 7.51 (dd, J ¼ 14.2, 6.4, 1 H); 7.26 (d, J ¼ 7.9, 2 H); 5.07 (dd, J ¼ 13.6, 1.4, 1 H); 4.69 (dd,
J ¼ 6.3, 1.4, 1 H); 2.42 (s, 3 H). 13C-NMR (100 MHz, CDCl3): 163.6; 144.3; 141.4; 129.9; 129.5; 126.1;
97.8; 21.6.
Ethenyl Benzoate (4b) [15]. Yield: 60%. IR (KBr): 3088, 2944, 2840, 1743, 1645, 1601, 1582, 1492,
1465, 1437, 1302. 1H-NMR (400 MHz, CDCl3): 8.12 (d, J ¼ 9.7, 2 H); 7.45 – 7.62 (m, 4 H); 5.09 (dd, J ¼
14.2, 2.0, 1 H); 4.71 (dd, J ¼ 6.4, 1.5, 1 H). 13C-NMR (100 MHz, CDCl3): 163.6; 141.4; 133.6; 129.9;
128.9; 128.5; 98.2.
Ethenyl 4-Fluorobenzoate (4c) [7]. Yield: 66%. IR (KBr): 1733, 1645, 1605, 1508, 1267, 1138.
1H-NMR (400 MHz, CDCl3): 8.14 (m, 2 H); 7.51 (dd, J ¼ 13.7, 6.3, 1 H); 7.16 (m, 2 H); 5.08 (dd, J ¼ 14.2,
1.5, 1 H); 4.71 (dd, J ¼ 6.4, 2.0, 1 H). 13C-NMR (100 MHz, CDCl3): 166.1 (d, J(C,F) ¼ 254); 162.6 (s);
141.3 (s); 132.6 (d, J(C,F) ¼ 10); 125.2 (d, J(C,F) ¼ 3); 115.7 (d, J(C,F) ¼ 22); 98.3 (s).
Ethenyl 4-Bromobenzoate (4d). Yield: 58%. M.p. 58 – 608 [15]. IR (KBr): 3093, 1926, 1736, 1648,
1
1589, 1485, 1398, 1301, 1270, 1175. H-NMR (400 MHz, CDCl3): 7.97 (d, J ¼ 8.8, 2 H); 7.63 (d, J ¼ 8.3,
2 H); 7.51 (dd, J ¼ 13.7, 6.4, 1 H); 5.09 (dd, J ¼ 14.2, 2.0, 1 H); 4.73 (dd, J ¼ 6.3, 1.0, 1 H). 13C-NMR
(100 MHz, CDCl3): 162.9; 141.2; 131.9; 131.4; 128.9; 127.8; 98.5.
Ethenyl 3-(Trifluoromethyl)benzoate (4e). Yield: 43%. IR (KBr): 2931, 1742, 1651, 1619, 1445, 1398,
1337, 1243, 1171, 1134. 1H-NMR (400 MHz, CDCl3): 8.36 (s, 1 H); 8.30 (d, J ¼ 7.8, 1 H); 7.87 (d, J ¼ 7.8,
1 H); 7.65 (t, J ¼ 7.8, 1 H); 7.53 (dd, J ¼ 13.7, 5.9, 1 H); 5.15 (dd, J ¼ 14.2, 1.8, 1 H ); 4.78 (dd, J ¼ 6.3, 1.9,
1 H). 13C-NMR (100 MHz, CDCl3): 162.3 (s); 141.2 (s); 133.1 (s); 131.3 (q, J(C,F) ¼33); 130.0 (q,
J(C,F) ¼ 4); 129.8 (s); 129.2 (s); 126.8 (q, J(C,F) ¼ 4); 123.5 (q, J(C,F) ¼ 271); 98.9 (s).
Ethenyl 3-Nitrobenzoate (4f). Yield: 58%. M.p. 57 – 598 [16]. IR (KBr): 3097, 2920, 2860, 1739, 1648,
1617, 1534, 1479, 1352, 1324, 1302, 1256, 1138. 1H-NMR (400 MHz, CDCl3): 8.90 (t, J ¼ 2.0, 1 H); 8.43 –
8.48 (m, 2 H); 7.72 (t, J ¼ 7.8, 1 H); 7.54 (dd, J ¼ 13.7, 6.3, 1 H); 5.19 (dd, J ¼ 13.7, 2.0, 1 H); 4.82 (dd, J ¼
5.9, 2.0, 1 H). 13C-NMR (100 MHz, CDCl3): 161.6; 148.3; 141.0; 135.5; 130.7; 129.8; 127.8; 124.8; 99.4.
Ethenyl 4-Nitrobenzoate (4g). Yield: 44 %. M.p. 75 – 778 [7]. IR (KBr): 3110, 2857, 1953, 1739, 1648,
1600, 1529, 1412, 1354, 1298, 1270, 1134, 1103. 1H-NMR (400 MHz, CDCl3): 8.27 – 8.33 (m, 4 H); 7.53 (dd,
J ¼ 14.2, 6.4, 1 H); 5.17 (dd, J ¼ 14.2, 1.5, 1 H); 4.81 (dd, J ¼ 6.4, 2.0, 1 H). 13C-NMR (100 MHz, CDCl3):
161.7; 150.8; 141.1; 134.3; 131.1; 123.6; 99.4.
Ethenyl 4-Methoxybenzoate (4h). Yield: 70%. M.p. 61 – 638 [17]. IR (KBr): 3403, 1931, 1724, 1648,
1607, 1584, 1514, 1425, 1299, 1261, 1180, 1145, 1099. 1H-NMR (400 MHz, CDCl3): 8.07 (d, J ¼ 9.2, 2 H);
7.52 (dd, J ¼ 14.2, 6.3, 1 H); 6.95 (d, J ¼ 8.8, 2 H); 5.05 (dd, J ¼ 13.7, 1.5, 1 H); 4.67 (dd, J ¼ 6.4, 1.5, 1 H);
3.87 (s, 3 H). 13C-NMR (100 MHz, CDCl3): 163.9; 163.3; 141.5; 132.1; 121.2; 113.8; 97.6; 55.4. HR-ESI-
MS (pos.): 179.0708 ([M þ H]þ, C10H11Oþ3 ; calc. 179.0703).
Ethenyl 3,4-Dimethoxybenzoate (4i). Yield: 56%. M.p. 57 – 598. IR (KBr): 3008, 1728, 1653, 1601,
1517, 1470, 1352, 1297, 1280, 1186. 1H-NMR (400 MHz, CDCl3): 7.77 (d, J ¼ 6.8, 1 H); 7.58 (s, 1 H); 7.52
(dd, J ¼ 13.7, 6.3, 1 H); 6.92 (d, J ¼ 8.3, 1 H); 5.07 (dd, J ¼ 13.7, 1.5, 1 H); 4.69 (dd, J ¼ 5.9, 1.5, 1 H); 3.95

Helvetica Chimica Acta – Vol. 97 (2014)
1121
(s, 6 H). 13C-NMR (100 MHz, CDCl3): 163.3; 153.5; 148.7; 141.5; 124.2; 121.2; 112.1; 110.3; 97.7; 55.9.
HR-ESI-MS (pos.): 209.0814 ([M þ H]þ, C11H13O4þ ; calc. 209.0824).
Ethenyl 2-Bromobenzoate (4j). Yield: 45%. IR (KBr): 3009, 2840, 1728, 1653, 1601, 1517, 1471, 1352,
1296, 1279, 1220. 1H-NMR (400 MHz, CDCl3): 7.92 (d, J ¼ 6.3, 1 H); 7.71 (d, J ¼ 8.8, 1 H); 7.51 (dd, J ¼
14.2, 6.3, 1 H); 7.37 – 7.39 (m, 2 H); 5.09 (dd, J ¼ 13.7, 1.5, 1 H); 4.75 (dd, J ¼ 6.4, 2.0, 1 H). 13C-NMR
(100 MHz, CDCl3): 162.6; 141.1; 134.6; 133.1; 131.7; 130.4; 127.1; 122.3; 98.8.
Ethenyl 1,3-Dimethyl-1H-pyrazole-5-carboxylate (4k). Yield: 44%. IR (KBr): 3094, 2956, 1738, 1646,
1537, 1446, 1295, 1242. 1H-NMR (400 MHz, CDCl3): 7.43 (dd, J ¼ 14.2, 6.4, 1 H); 6.71 (s, 1 H); 5.05 (dd,
J ¼ 14.1, 1.9, 1 H); 4.72 (dd, J ¼ 5.8, 1.4, 1 H); 4.10 (s, 3 H); 2.20 (s, 3 H). 13C-NMR (100 MHz, CDCl3):
156.8; 147.2; 140.5; 131.5; 111.1; 98.7; 39.1; 13.2.
Ethenyl Thiophene-2-carboxylate (4l). Yield: 48%. IR (KBr): 3019, 2400, 1723, 1523, 1419, 1215, 929,
770, 669. 1H-NMR (400 MHz, CDCl3): 7.90 (d, J ¼ 3.9, 1 H); 7.64 (d, J ¼ 4.9, 1 H); 7.47 (dd, J ¼ 14.1, 6.3,
1 H); 7.15 (t, J ¼ 3.4, 1 H); 5.07 (dd, J ¼ 14.2, 1.9, 1 H); 4.70 (dd, J ¼ 6.3, 1.4, 1 H). 13C-NMR (100 MHz,
CDCl3): 159.2; 141.0; 134.5; 133.5; 132.3; 127.9; 98.2.
Ethenyl 6-[(Ethoxycarbonyl)oxy]naphthalene-1-carboxylate (4m). Yield: 35%. M.p. 137 – 1408. IR
(KBr): 3436, 2917, 1757, 1731, 1647, 1274, 1194, 1139. 1H-NMR (400 MHz, CDCl3): 8.86 (s, 1 H); 8.14 (d,
J ¼ 8.3, 1 H); 8.02 (d, J ¼ 8.8, 1 H); 7.89 (d, J ¼ 8.8, 1 H); 7.72 (s, 1 H); 7.59 (dd, J ¼ 13.7, 6.4, 1 H); 7.43
(d, J ¼ 9.3, 1 H); 5.16 (dd, J ¼ 14.2, 2.0, 1 H); 4.76 (dd, J ¼ 6.3, 1.9, 1 H); 4.40 (q, J ¼ 6.8, 1 H); 1.44 (t,
J ¼ 6.8, 1 H). 13C-NMR (100 MHz, CDCl3): 141.5; 131.5; 131.2; 128.2; 126.2; 126.1; 121.7; 118.1; 98.4;
65.2; 14.2. HR-ESI-MS (pos.): 287.0919 ([M þ H]þ, C18H15O5þ ; calc. 287.0925).
Ethenyl 1-Benzyl-1H-indole-3-carboxylate (4n). Yield: 38%. IR (KBr): 3439, 2918, 1716, 1731, 1647,
1
1536, 1271, 1249, 1148. H-NMR (400 MHz, CDCl3): 8.25 (d, J ¼ 6.9, 1 H); 7.93 (s, 1 H); 7.60 (dd, J ¼
14.2, 6.3, 1 H); 7.28 – 7.34 (m, 5 H); 7.17 (t, J ¼ 1.9, 2 H); 5.36 (s, 2 H); 5.03 (dd, J ¼ 13.7, 1.5, 1 H);
4.63 (dd, J ¼ 6.4, 1.5, 1 H). 13C-NMR (100 MHz, CDCl3): 141.3; 135.6; 135.4; 129.0; 128.2; 127.1; 123.3;
122.4; 121.8; 110.5; 96.6; 50.9. HR-ESI-MS (pos.): 278.1181 ([M þ H]þ, C18H16NO2þ ; calc. 278.1159).
Ethenyl 2,2-Dimethylpropanoate; (4o). Yield: 39%. 1H-NMR (400 MHz, CDCl3): 7.28 (dd, J ¼ 14.2,
6.3, 1 H); 4.92 (dd, J ¼ 13.7, 1.5, 1 H); 4.58 (dd, J ¼ 6.4, 1.5, 1 H); 1.23 (s, 9 H).
Ethenyl 2-Bromo-5-nitrobenzoate (4p). Yield: 42%. M.p. 65 – 678. IR (KBr): 3444, 2919, 1752, 1644,
1607 1532, 1350, 1310, 1237. 1H-NMR (400 MHz, CDCl3): 8.74 (s, 1 H); 8.23 (d, J ¼ 8.8, 1 H); 7.93 (d, J ¼
8.8, 1 H); 7.51 (dd, J ¼ 13.7, 6.4, 1 H); 5.19 (dd, J ¼ 14.2, 1.9, 1 H); 4.84 (dd, J ¼ 6.3, 2.4, 1 H). 13C-NMR
(100 MHz, CDCl3): 161.6; 141.6; 136.7; 132.5; 130.5; 127.9; 127.4; 100.8.
Ethenyl 2,5-Dibromo-4-methylbenzoate; 4q): Yield: 44%. M.p. 101 – 1038. IR (KBr): 3445, 2920,
1741, 1649, 1587, 1474, 1234. 1H-NMR (400 MHz, CDCl3): 8.10 (s, 1 H); 7.58 (s, 1 H); 7.48 (dd, J ¼ 13.7,
6.3, 1 H); 5.12 (dd, J ¼ 13.7, 1.5, 1 H); 4.76 (dd, J ¼ 6.4, 2.0, 1 H); 2.41 (s, 3 H). 13C-NMR (100 MHz,
CDCl3): 161.3; 144.3; 141.1; 136.5; 135.4; 128.8; 123.5; 121.2; 99.1; 22.8. HR-ESI-MS (pos.): 318.8969
([M þ H]þ, C10H9Br2Oþ2 ; calc. 318.9001).
Synthesis of 3-Methylidene-2-benzofuran-1(3H)-one (7a). A Schlenk flask was charged with 4j (1 g,
4.4 mmol), dry K2CO3 (1.8 g, 13.2 mmol), Pd(PPh3)4 (0.3 mol-%), and toluene. The flask was purged
with N2, and then, the mixture heated to 1008 under stirring. The progress of the reaction was monitored
by TLC. After 12 h, additional Pd(PPh3)4 (0.1 mol-%) was added, and the mixture was heated for
additional 12 h, then cooled to r.t. The mixture was diluted with toluene, filtered, and concentrated. The
crude product was purified further by CC (SiO2; hexane/AcOEt 98 :2) to give off-white solid. Yield:
86%. M.p. 54 – 568 [18]. IR (KBr): 3445, 2924, 1773, 1638, 1467, 1287. 1H-NMR (400 MHz, CDCl3): 7.93
(d, J ¼ 7.31, 1 H); 7.73 (d, J ¼ 3.9, 2 H); 7.57 – 7.61 (m, 1 H); 5.25 (dd, J ¼ 6.4, 2.9, 2 H). 13C-NMR
(100 MHz, CDCl3): 166.8; 151.8; 138.9; 134.4; 130.4; 125.2; 120.6; 91.2.
1H-Indene-1,3(2H)-dione (9) [19]. Yield: 64%. M.p. 130 – 1328. IR (KBr): 3428, 2918, 1744, 1706,
1
1586, 1351, 1256. H-NMR (400 MHz, CDCl3): 7.97 – 8.01 (m, 2 H); 7.83 – 7.87 (m, 2 H); 3.25 (s, 2 H).
13C-NMR (100 MHz, CDCl3): 197.4; 143.3; 135.5; 123.1; 44.9.
6-Bromo-5-methyl-3-methylidene-2-benzofuran-1(3H)-one (7b). Yield: 83%. IR (KBr): 3446, 2924,
1741, 1649, 1474, 1285, 1234, 1142. 1H-NMR (400 MHz, CDCl3): 8.07 (s, 1 H); 7.75 (s, 1 H); 5.24 (dd, J ¼
15.7, 3.0, 2 H); 2.59 (s, 3 H). 13C-NMR (100 MHz, CDCl3): 158.3; 151.3; 145.4; 138.1; 128.9; 127.4; 124.6;
122.2; 91.6; 24.0. HR-ESI-MS (pos.): 238.9708 ([M þ H]þ, C10H7BrO2þ ; calc. 238.9727).

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Helvetica Chimica Acta – Vol. 97 (2014)
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Received November 6, 2013