Pd/C-Cu mediated direct and one-pot synthesis of γ-ylidene butenolides

Article abstract of DOI:10.1016/j.tetlet.2013.02.040

10% Pd/C in combination with CuI, PPh₃, and Et₃N has been identified as an effective catalyst system for the coupling of (Z)-3-iodoacrylic acid with terminal alkynes in 1,4-dioxane leading to the one-pot synthesis of γ-ylidene butenolides. The methodology showed remarkable regio- and stereoselectivity as only the five-membered lactone ring products were formed with an exocyclic double bond possessing Z-geometry.

Full text of DOI:10.1016/j.tetlet.2013.02.040

Tetrahedron Letters 54 (2013) 2151–2155
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Pd/C–Cu mediated direct and one-pot synthesis of
c-ylidene butenolides
a
b
c
a
d,
⇑
D. Rambabu , S. Bhavani , Kumara Swamy Nalivela , Soumita Mukherjee , M. V. Basaveswara Rao
Manojit Pal
a
,
a,
⇑
Dr. Reddy’s Institute of Life Sciences, University of Hyderabad Campus, Gachibowli 500 046, Hyderabad, India
Department of Chemistry, K.L. University, Vaddeswaram, Guntur 522 502, Andhra Pradesh, India
Organic Chemistry Institute, University of Heidelberg, Im Neuenheimer Feld 271, 69120 Heidelberg, Germany
Department of Chemistry, Krishna University, Machilipatnam 521 001, Andhra Pradesh, India
b
c
d
a r t i c l e i n f o
a b s t r a c t
Article history:
3 3
10% Pd/C in combination with CuI, PPh , and Et N has been identified as an effective catalyst system for
Received 6 January 2013
Revised 11 February 2013
Accepted 13 February 2013
Available online 20 February 2013
the coupling of (Z)-3-iodoacrylic acid with terminal alkynes in 1,4-dioxane leading to the one-pot synthe-
sis of -ylidene butenolides. The methodology showed remarkable regio- and stereoselectivity as only the
five-membered lactone ring products were formed with an exocyclic double bond possessing
c
Z-geometry.
Ó 2013 Elsevier Ltd. All rights reserved.
Keywords:
Pd/C
Coupling
Cyclization
Butenolides
The growing requirements of chemical and pharmaceutical
industries have prompted synthetic chemists to devote their
continuing efforts in the development of more efficient, effective,
and safer chemical reactions or methodologies. The heterogeneous
catalysis has attracted particular attention for this purpose as the
catalyst used can be separated easily and potentially be recovered
and recycled several times thereby enhancing the efficiency and
effectiveness of the reaction.
tion of alkynes possessing a carboxylic acid moiety in close prox-
imity to the triple bond has become a common method for the
construction of
c-butenolide structures. For example, lactonization
of 4-alkynoic acids (D) afforded
c-ylidene butenolide (E) following
a 5-exo cyclization (Fig. 2). However, in addition to E formation of
six-membered d-lactone (F) was also observed in these cases as a
result of 6-endo cyclization (Fig. 2). A wide range of transition me-
tal based catalysts (e.g., Ag, Hg, Rh, Pd, Zn, Au, etc.) have shown to
promote the intramolecular addition of carboxylic acids to al-
The
c-(alkyl/aryl)idene butenolides belonging to the lactone
4
,5
family are common structural frameworks found in many naturally
kynes. Generally, b-iodopropenoic acid has been used as a key
precursor and the synthesis of -butenolides via the reaction of
occurring compounds and possess a wide range of pharmacological
c
1
activities. For example, Freelingyne (A, Fig. 1), a sesquiterpene from
b-iodopropenoic acid and terminal alkynes has been carried out
in two separate steps, for example, (i) Sonogashira type coupling
leading to the 4-alkynoic acid derivatives followed by (ii) cycliza-
1
c
1d
Eremophila freelingii, or dihydroxerulin (B, Fig. 1), an inhibitor of
1d
cholesterol biosynthesis or the carotinoid peridinin which plays a
dominant role in marine photosynthesis or anti-inflammatory lu-
peol acetate belongs to this class. Due to our interest in buteno-
lides as potential anti-inflammatory agents2 we planned to
construct a library of diversity based small molecules C (Fig. 1)
tion mediated by metal complexes, bases, and halogen.8 Thus,
6
7
1
e
synthesis of
c-alkylidene butenolides has been reported via the
palladium-mediated cross coupling of alkynylzinc with b-haloac-
9
2 3
rylic acid followed by lactonization catalyzed by Ag CO . This
based on
macological evaluation. We anticipated that depending on the nat-
ure of -substituent present these simple lactones may show
c
-(alkyl/aryl)idene butenolide framework for their phar-
methodology though involved two-steps, was found to be a supe-
rior alternative to the one pot method reported earlier.10 While
these reactions were found to be quite effective the methodology,
however, involved the use of relatively expensive palladium cata-
c
promising pharmacological properties.
Due to their enormous importance in chemical and pharmaceu-
tical research several methods leading to C have been reported.
However, over the past decade transition metal-mediated cycliza-
lysts, that is, (PPh
due to their decomposition during the aqueous workup. Recently,
-alkylidene butenolides and isocoumarins have been synthesized
by using Cu(I)-salt under
palladium-free condition.11 The
3 4 3 2 2
) Pd and (PPh ) PdCl that were not recoverable
3
c
a
methodology, however, involved the use of relatively high catalyst
loading, that is, 20 mol % of CuI. Over the years our group has
⇑
Corresponding authors. Tel.: +91 40 6657 1500; fax: +91 40 6657 1581.
E-mail address: manojitpal@rediffmail.com (M. Pal).
0
040-4039/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2013.02.040

2
152
D. Rambabu et al. / Tetrahedron Letters 54 (2013) 2151–2155
R
O
O
O
n-C H7
O
3
O
O
O
A (Freelingyne)
B (Dihydroxerulin)
C
Figure 1. Biologically active
c
-alkylidene butenolides (A & B) and our target compounds C.
HI, H O
2
CO H
I
O
2
Path b
6-endo)
Path a
80 °C, 12h
53%
HO
4
O
1
O
OH
(
(5-exo)
O
Scheme 2. Preparation of (Z)-3-iodoacrylic acid (1).
O
O
F
D
E
mostly in these cases the formation of traces of other regioisomer
cannot be ruled out completely in these solvents. However, since
the best result was achieved by using 1,4-dioxane as a solvent,
all other studies were carried out using 1,4-dioxane. The role of
catalyst, co-catalyst, and ligand was also examined. The yield of
3a was decreased significantly when the reaction was performed
Figure 2. Lactonization of 4-alkynoic acids.
focused on the use of Pd/C as an efficient and effective catalyst for
various C–C bond forming reactions either in pure water or other
1
2
organic solvents. The advantages of Pd/C is that it is stable, easy
to handle, and separable from the product. Additionally, the cata-
lyst can be recovered and recycled. Its industrial application in
hydrogenation reaction is well documented and being practiced
over several decades. All these features prompted us to explore
the use of commercially available 10% Pd/C as an alternative cata-
in the absence of any one of Pd/C, CuI, and PPh
7–9) indicating the key role played by the combined form of these
catalysts. We also examined the role of Et N in the present cou-
3
(Table 1, entries
3
pling-cyclization reaction in the absence of which the reaction
did not proceed. All these reactions were performed under a nitro-
gen atmosphere. An attempt to perform the reaction under air led
to the formation of 1,4-diphenylbuta-1,3-diyne as a major product
due to the dimerization of 2a in the presence of aerial oxygen.
Overall, the reaction conditions presented in the entry 1 of Table
1 were found to be optimum for the preparation of 3a.
lyst in the direct, one-pot, and regioselective synthesis of c-ylidene
butenolides. Herein we report our initial findings on Pd/C–Cu med-
iated coupling of terminal alkynes with (Z)-3-iodoacrylic acid lead-
ing to the practical synthesis of c-ylidene butenolides (Scheme 1).
To the best of our knowledge, such a Pd/C–Cu mediated coupling-
cyclization strategy for the synthesis of this class of lactones has
not been explored earlier.
To expand the scope of the present Pd/C–Cu mediated synthesis
of c-ylidene butenolide, a variety of terminal alkynes (2) were re-
The key starting material, that is, (Z)-3-iodoacrylic acid (1) re-
quired for our synthesis was conveniently prepared13 via the reac-
tion of propiolic acid (4) with HI in water (Scheme 2). Initially, the
coupling reaction of (Z)-3-iodoacrylic acid (1) with phenyl acety-
lene (2a) was examined in the presence of 10% Pd/C (0.026 equiv),
Table 1
Effect of reaction conditions on Pd/C-mediated reaction of (Z)-3-iodoacrylic acid (1a)
with phenyl acetylene (2a)
a
PPh
various solvents (Table 1). The (Z)-5-benzylidenefuran-2(5H)-one
3c) was isolated in 84% yield (Table 1, entry 1) when the reaction
3
(0.20 equiv), CuI (0.05 equiv), and triethylamine (3.0 equiv) in
1
0% Pd/C, PPh3
O
O
CuI, Et N
3
(
I
O
Solvent
8
was performed in 1,4-dioxane for 3 h. The formation of corre-
sponding six-membered lactone was not detected in this case.
The increase of reaction time did not improve the product yield
further (Table 1, entry 2). To test the recyclability of Pd/C, the cat-
alyst was recovered and reused for additional three runs when the
HO
0 °C
1
2a
3a
1
4a
Entry
Solvent
Time (h)
% Yieldb
product 3a was isolated in 75%, 71%, and 67% yields respectively.
1
2
3
4
5
6
7
8
9
1,4-Dioxane
1,4-Dioxane
MeOH
3
6
6
3
10
3
3
3
3
3
84
85
The use of other solvents such as MeOH, EtOH, MeCN, and DMF
was examined but found to be less effective in terms of product
yields (Table 1, entries 3–6). Indeed, the product 3c was isolated
only in 58% yield when the reaction was performed in MeCN even
after 10 h (Table 1, entry 5). The yields were marginally improved
when MeOH or EtOH was used (Table 1, entries 3 and 4). It is wor-
thy to mention that while we recovered the starting materials
c
63
EtOH
MeCN
DMF
77
58
60
d
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
17
36
35
e
f
g
10
0
a
All the reactions were carried out by using 1 (0.89 mmol), 2a (1.33 mmol), 10%
Pd/C (0.023 mmol), PPh (0.092 mmol), CuI (0.046 mmol), and Et N (2.67 mmol) in
a solvent under a nitrogen atmosphere.
3
3
1
0% Pd/C, PPh3
CuI, Et N
b
3
O
Isolated yields.
The reaction was performed at 60 °C.
The reaction was performed in the absence of CuI.
The reaction was performed in the absence of 10% Pd/C.
The reaction was performed in the absence of PPh .
3
3
The reaction was performed in the absence of Et N.
I
O
R
O
c
1
3
,4-Dioxane
h, 80 °C
R
d
HO
3
e
1
2
f
g
Scheme 1. Pd/C–Cu mediated synthesis of c-ylidene butenolides.

D. Rambabu et al. / Tetrahedron Letters 54 (2013) 2151–2155
2153
Table 2
Pd/C-mediated preparation of
Table 2 (continued)
c
-alkylidene butenolides (Scheme 1)a
Entry
Substrate (2)
OPMB
2j
Productsb (3)
% Yieldc
Entry
Substrate (2)
Productsb (3)
% Yieldc
OMe
O
O
O
10
70
O
1
2a
72
O
3j
3a
O
1
1
2
68
65
O
O
O
2
3
2b
75
84
O
2
k
3k
3
b
1
OH
O
O
O
O
2l
3l
2c
THP = tetrahydro-2H-pyran-2-yl; PMB = p-methoxybenzyl.
All the reactions were carried out by using 1 (0.89 mmol), 2 (1.33 mmol), 10%
Pd/C (0.023 mmol), PPh (0.092 mmol), CuI (0.046 mmol), and Et N (2.67 mmol) in
OH
a
3
3
3
c
1
,4-dioxane (5.0 mL) at 80 °C for 3 h under a nitrogen atmosphere.
b
c
Identified by 1H NMR, IR, mass.
Isolated yield.
O
OH
4
5
6
80
82
72
2
d
acted with 1 under the condition14b of entry 1 of Table 1. The re-
sults are summarized in Table 2. The presence of aryl (2a, 2e),
cycloalkyl (2b), hydroxy alkyl (2c, 2d) or their protected form (2i,
2j), heteroaryl (2f), and alkenyl moiety (2k, 2l) in the terminal al-
kynes employed was well tolerated. The use of trimethylsilyl acet-
ylene (2g) however afforded 5-methylenefuran-2(5H)-one (3g) in
OH
3d
CH3
O
O
2
e
low yield. Nevertheless, a range of c-ylidene butenolides (3) were
synthesized in good yields (except the butenolide 3g) without for-
mation of the corresponding regioisomeric six-membered lactones.
We also examined the coupling-cyclization of (Z)-3-bromoacrylic
CH3
3e
1
0
acid with 2a when the desired product 3a was isolated in 70%
yield after 12 h under the conditions employed. It is worthy to
mention that all these reactions were performed using a 1:4:2 ratio
of 10% Pd/C, PPh3, and CuI with a low catalyst loading, that is,
N
O
O
2f
N
2
.6 mol % of 10% Pd/C and 5.2 mol % of CuI for each reaction. More-
over, no significant dimerization of terminal alkynes (i.e., forma-
tion of R–„–„–R as a result of Glasser coupling) as a side
reaction was observed during the present synthesis of 3. However,
3f
9
SiMe3
2g
the starting material 1 was recovered in some of the cases where
the yield of product 3 was not particularly high. The compound
O
7
8
O
15
75
3
g
3
d can be converted into the polyene natural product dihydroxer-
OEt
ulin (B, Fig. 1) via an organocatalytic IBX-mediated dehydrogena-
tion process of simple alcohols to enals as a key step.15 Though
the reaction proceeded well with the alkyl ether 2j, the use of an
arylether, for example, (prop-2-ynyloxy)benzene was not success-
ful as it underwent depropargylation reaction under the conditions
O
O
EtO
2
h
2
EtO
OEt
3
h
1
6
employed. Nevertheless, the use of Pd/C–Cu mediated coupling-
cyclization strategy in 1,4-dioxane presented here appeared as a
OTHP
O
O
useful and faster method for accessing
c-ylidene butenolides.
i
1
7
O
Based on the spectral data and comparing them with that re-
9
72
11
ported in the literature all the compounds synthesized were
O
found to possess Z-stereochemistry around the exocyclic double
bond. Thus the present approach to
peared to be a regio and stereoselective one.
c-ylidene butenolides ap-
3
i
We have demonstrated that combination of 10% Pd/C–CuI–PPh
3
3
in the presence of Et N facilitated the coupling-cyclization of (Z)-3-

2
154
D. Rambabu et al. / Tetrahedron Letters 54 (2013) 2151–2155
Pd/C
Pd
leaching
Generation
of actual
catalytic
species
Precipitation of
Pd on C at the end
of catalytic cycle
Pd in
solution
B
1
I
PPh3
O
BH+I-
R
BH+
O
Pd(0)-PPh3
complex in
solution
O
3
O
Cu
BH+I-
CuI, B
CuI, BH+
The catalytic cycle
B = Et N)
Intramolecular
cyclization
(
3
R
Pd
O
I
B
BH+I-
+
Pd(0)
BH+
O
CuI/Et N
BH+
3
O
E-1
Cu
R
O
E-2
Pd
O
R
O
BH+
3
Scheme 3. Proposed mechanism for the one-pot synthesis of c-alkylidene butenolides (3) under the catalysis of Pd/C–CuI–PPh .
iodoacrylic acid with terminal alkynes via C–C bond forming reac-
tion as a key step. A proposed mechanism for the one-pot synthesis
step and afforded a range of desired products under mild conditions.
The merits and demerits of the methodology are presented. The
methodology showed remarkable regio- and stereoselectivity as
only the five-membered lactone ring products were formed with
an exocyclic double bond possessing (Z-geometry). Due to its oper-
ational simplicity, relatively low catalyst loading, and the use of
inexpensive and stable Pd/C the methodology has potential to be-
come a useful alternative to the existing methods for accessing
of
c-alkylidene butenolides (3) under the catalysis of Pd/C–CuI–
PPh
3
is shown in Scheme 3. The reaction seemed to proceed via
three key steps, that is, (a) the generation of actual catalytic spe-
cies, (b) alkynylation of iodo compound 1 and (c) intramolecular
cyclization of the resulting enynoic acid under regio- and stereo-
control conditions. The alkynylation step proceeds via generation
of an active Pd(0) species in situ that produces the organo-Pd(II)
species E-1 via oxidative addition with 1. The active Pd(0) species
is generated via a Pd leaching process18 into the solution [from the
minor portion of the bound palladium (Pd/C)] followed by interac-
diversity based c-alkylidene butenolides.
Acknowledgments
tions with the phosphine ligands. The dissolved Pd(0)–PPh
plex then catalyzes the C–C bond forming reaction in solution via
i) trans organometallation with copper acetylide generated
3
com-
The authors thank the management of Dr. Reddy’s Institute of
Life Sciences for continuous support and encouragement. S.M.
thanks CSIR, New Delhi, India, for a Research Associate Fellowship.
(
in situ from CuI and terminal alkyne 2 followed by (ii) reductive
elimination of Pd(0) to afford the enynoic acid E-2. The acid E-2
thus formed subsequently undergoes Cu-mediated 5-exo-dig ring
closure in an intramolecular fashion to give the five-membered
ring product (3). It appears that the catalytic cycle works in solu-
tion rather than on the surface and at the end of the reaction re-
precipitation of Pd occurs on the surface of the charcoal.
References and notes
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2
.
8
a
ing to a known method was treated with CuI in the presence of
Et N in 1,4-dioxane at 80 °C for 3 h when the corresponding
-alkylidene butenolide 3a was isolated in 61% yield. This clearly
3
c
suggested that the intramolecular cyclization of E-2 via C–O bond
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1
9
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presence of Et N allowed coupling of (Z)-3-iodoacrylic acid with
terminal alkynes in 1,4-dioxane leading to the one-pot synthesis
of -ylidene butenolides. The present coupling-cyclization based
methodology proceeded via a C–C bond forming reaction as a key
3
in the
3
c

D. Rambabu et al. / Tetrahedron Letters 54 (2013) 2151–2155
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17. Spectral data of selected compounds: compound 3a: pale yellow solid; mp 87–
1
89 °C; H NMR (CDCl
3
, 400 MHz): d 6.02 (s, 1H), 6.20 (d, J = 6 Hz, 1H), 7.31–7.48
13
(m, 5H), 7.78 (d, J = 6 Hz, 1H); C NMR (CDCl
129.2, 130.7, 132.8, 145.1, 148.3, 170.1; IR (KBr): 1787, 1762, 1550 cm ; MS
3
, 100 MHz): d 114.2, 118.0, 128.7,
À1
+
1
7
.
(ESI): m/z ([M+H] ): 173. Compound 3d: H NMR (CDCl
(m, 2H), 2.30 (br, 1H), 2.44–2.46 (m, 2H), 3.61 (t, J = 6.5 Hz, 2H), 5.32 (t,
J = 8.0 Hz, 1H), 6.10 (d, J = 5.5 Hz, 1H), 7.32 (d, J = 5.0 Hz, 1H); 13C NMR (CDCl
100 MHz): d 22.7, 31.5, 61.6, 116.7, 118.8, 143.5, 149.7, 170.0; MS (ESI): m/z
3
, 400 MHz): d 1.70–1.73
3
,
1
986, 2133.
+
1
8
.
.
(a) Biagetti, M.; Bellina, F.; Carpita, A.; Stabile, P.; Rossi, R. Tetrahedron 2002, 58,
3
([M+H] ): 154.9. Compound 3f: ash colored solid; mp 82–84 °C. H NMR (CDCl ,
5
2
023; (b) Bellina, F.; Biagetti, M.; Carpita, A.; Rossi, R. Tetrahedron 2001, 57,
857; (c) Sofia, M. J.; Katzenellenbogen, J. A. J. Med. Chem. 1986, 29, 230.
400 MHz): d 6.32 (dd, J = 5.5 and 1.7 Hz, 1H), 6.56 (br d, J = 1.2 Hz, 1H), 7.15
(dd, J = 7.6 and 4.5 Hz, 1H), 7.30 (d, J = 7.7 Hz, 1H), 7.66 (td, J = 7.7 and 1.8 Hz,
9
Liu, F.; Negishi, E. J. Org. Chem. 1997, 62, 8591.
1H), 8.60 (br d, J = 4.5 Hz, 1H), 8.78 (dd, J = 5.5 and 0.6 Hz, 1H); 13C NMR (CDCl
3
,
1
1
0. Kotora, M.; Negishi, E. Synthesis 1997, 121.
100 MHz): d 113.2, 122.1, 123.1, 126.3, 132.5, 137.0, 144.1, 150.3, 153.2, 169.6;
+
À1
1. Inack-Ngi, S.; Rahmani, R.; Commeiras, L.; Chouraqui, G.; Thibonnet, J.;
Duchene, A.; Abarbri, M.; Parrain, J. Adv. Synth. Catal. 2009, 351, 779.
2. For a review, see: Pal, M. Synlett 2009, 2896.
3. Suh, Y.-G.; Jung, J.-K.; Seo, S.-Y.; Min, K.-H.; Shin, D.-Y.; Lee, Y.-S.; Kim, S.-H.;
Park, H.-J. J. Org. Chem. 2002, 67, 4127.
IR (KBr): 1787, 1763, 1584, 1550 cm ; MS (ESI): m/z ([M+H] ): 174. Compound
3h: 1H NMR (CDCl
, 400 MHz): d 1.23 (t, J = 7.0 Hz, 6H), 3.52–3.61 (m, 2H),
3.66–3.75 (m, 2H), 5.34 (d, J = 7.8 Hz, 1H), 5.47 (d, J = 7.8 Hz, 1H), 5.26 (dd,
J = 5.4 and 0.7 Hz, 1H), 7.37 (d, J = 5.4 Hz, 1H); 13C NMR (CDCl
, 100 MHz): d
3
1
1
3
+
15.5, 62.7, 96.8, 112.1, 121.5, 144.0, 150.1, 169.2; MS (ESI): m/z ([M+H] ):
198.9.
1
4. (a) The reaction was performed in a bigger scale using ꢀ100 mg of 10% Pd/C
(
0.092 mmol), PPh
3
(0.37 mmol), CuI (0.184 mmol), Et
3
N
(10.68 mmol),
18. The leaching of Pd in a Pd/C-mediated coupling reaction has been investigated
and confirmed earlier, see: Chen, J.-S.; Vasiliev, A. N.; Panarello, A. P.; Khinast, J.
G. Appl. Catal. A: Gen. 2007, 325, 76; see also Ref. 16. Additionally, in the case of
compound 1a (3.56 mmol), and acetylenic compound 2a (5.32 mmol) in 1,4-
dioxane (20.0 mL). After stirring at 80 °C for 3 h under nitrogen the mixture
was cooled to room temperature. The Pd/C was filtered off and washed with
water (2 Â 10 mL), acetone (2 Â 10 mL), and EtOAc (2 Â 10 mL). Then the
catalyst was collected, dried at 100 °C in an oven, and reused for the next run.
reaction of 1a with 2a when Pd/C–CuI–PPh
3
was hot filtered, after 20%
conversion, the filtrate continued to react, indicating that some of the
palladium was leaching from the surface and catalyzing the reaction. We
thank one of the reviewers for his suggestion to perform this hot filtration test
which is known to be a strong test for assessing the presence of soluble active
palladium in the filtrate.
The co-catalyst CuI along with PPh
General method for the preparation of 3: A mixture of compound 1 (0.89 mmol),
0% Pd/C (0.023 mmol), PPh (0.092 mmol), CuI (0.046 mmol), and Et
2.67 mmol) in 1,4-dioxane (5.0 mL) was stirred at 25 °C for 30 min under
3
was added in every repeated run. (b)
1
3
3
N
(
19. For a similar Ag-catalyzed cyclization, see: (a) Ogawa, Y.; Maruno, M.;
nitrogen. The acetylenic compound 2 (1.33 mmol) was added slowly with
stirring. The mixture was then stirred at 80 °C for 3 h, cooled to room
temperature, diluted with EtOAc (30 mL), and filtered through celite. The
filtrate was collected and concentrated. The residue was purified by column
chromatography (2–15% EtOAc/hexane) to afford the desired product.
Wakamatsu, T. Heterocycles 1995, 41, 2587; While cyclization of (Z)-5-
phenylpent-2-en-4-ynoic acid has been reported in the presence of pyridine
the reaction however required higher temperature and longer reaction time
(13 h), see: (b) Uchiyama, M.; Ozawa, H.; Takuma, K.; Matsumoto, Y.;
Yonehara, M.; Hiroya, K.; Sakamoto, T. Org. Lett. 2006, 8, 5517.