Dehydrogenative and decarboxylative C-H alkynylation of heteroarenes catalyzed by Pd(II)-carbene complex

Article abstract of DOI:10.1016/j.tet.2015.02.020

The direct alkynylation of heteroarenes was accomplished with easily prepared Pd(II) carbene complex (Pd Cat.) by two complementary strategies. Pd Cat. catalysed cross-dehydrogenative coupling of terminal alkynes with heteroarenes was achieved in the firs

Full text of DOI:10.1016/j.tet.2015.02.020

Accepted Manuscript
Dehydrogenative and decarboxylative C-H alkynylation of heteroarenes catalyzed by
Pd(II)-carbene complex
Thupakula Parsharamulu, Reddy Police Vishnuvardhan, Pravin R. Likhar, Mannepalli
Lakshmi Kantam
PII:
S0040-4020(15)00155-6
10.1016/j.tet.2015.02.020
TET 26409
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 13 November 2014
Revised Date: 22 January 2015
Accepted Date: 5 February 2015
Please cite this article as: Parsharamulu T, Vishnuvardhan RP, Likhar PR, Lakshmi Kantam M,
Dehydrogenative and decarboxylative C-H alkynylation of heteroarenes catalyzed by Pd(II)-carbene
complex, Tetrahedron (2015), doi: 10.1016/j.tet.2015.02.020.
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to
our customers we are providing this early version of the manuscript. The manuscript will undergo
copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please
note that during the production process errors may be discovered which could affect the content, and all
legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT
Graphical Abstract
To create your abstract, type over the instructions in the template box below.
Fonts or abstract dimensions should not be changed or altered.
Dehydrogenative and decarboxylative C-H
alkynylation of heteroarenes catalyzed by
Pd(II)-carbene complex
Leave this area blank for abstract info.
Parsharamulu Thupakula , Vishnuvardhan Reddy Police , Pravin R Likhar* and Lakshmi Kantam Mannepalli
Inorganic and Physical Chemistry Division, CSIR-Indian Institute of Chemical Technology, Hyderabad-500607,
India.

1
ACCEPTED MANUSCRIPT
Tetrahedron
journal homepage: www.elsevier.com
Dehydrogenative and decarboxylative C-H alkynylation of heteroarenes catalyzed by
Pd(II)-carbene complex
Parsharamulu Thupakula, Vishnuvardhan Reddy Police, Pravin R Likhar,* and Lakshmi Kantam
Mannepalli
CSIR-Inorganic and Physical Chemistry Division, Indian Institute of chemical Technology, Hyderabad-500607, India.
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
The direct alkynylation of heteroarenes was accomplished
with easily prepared Pd(II) carbene complex (Pd Cat.) by
two complementary strategies. Pd Cat. catalysed cross
dehydrogenative coupling of terminal alkynes with
heteroarenes was achieved in the first method and
decarboxylative coupling of aryl propiolic acids with
heteroarenes was investigated in the second method. Both
the methodologies tolerate a broad variety of heteroarenes
that include benzoxazoles, benzothiazoles, imidazole and
benzimidazoles.
Available online
Keywords:
Dehydrogenative
Decarboxylative
C-H alkylation
Alkynes
Azoles
2009 Elsevier Ltd. All rights reserved
.
———
Corresponding author. Tel.: +91-040-27193030; fax: +91-040-27160921; e-mail: mlakshmi@iict.res.in; plikhar@iict.res.in

2
Tetrahedron
1. Introduction
dehydrogenative coupling with terminal alkynes and other shows
ACCEPTED MANUSCRIPT
decarboxylative coupling of aryl propiolic acids.
The transition metal-mediated C-H bond activation has attracted
remarkable interest in modern organic chemistry.1 Direct
functionalization of C-H bond has facilitated the expedient synthesis
of numerous intricate novel molecules that was previously thought
O
N
Pd
N
impossible. The cross-dehydrogenative coupling (CDC) is
a
O
HO
prominent dual C-H bond activation strategy that has emerged as a
striking alternative to the traditional cross coupling reactions.2 CDC
is an atom and step-economical process for the construction of C-C
bond, which obviates the pre- functionalization of both coupling
partners. The CDC reactions are rather challenging because, in both
C-C cross coupling and arene C-H activation, chemo and
regioselectivity must be controlled to avoid the formation of
unwanted mixtures of regioisomeric homo- and hetero-coupled
products. These difficulties in direct functionalization of C-H bond
can be rather overcome by transition metal catalysts.3
Pd Cat.
Fig. 1 Anionic /amido carbocyclic carbene ligated palladium(II)
complex
2. Results and discussion
Initial studies were aimed to develop a catalytic protocol for cross-
dehydrogenative coupling strategy by C-H alkynylation of
benzoxazole 1a with phenylacetylene 2a. Thus, initial reaction was
performed using 0.5 mmol of 1a, 1 mmol of 2a, 1 mmol of oxidant,
1 mmol of base and 3 mol% of Pd Cat. in toluene at 85 °C. The
reaction yielded 42% desired product 2-(phenylethynyl)benzoxazole
3a (Table 1, entry 2).
Alkynyl substituted azoles act as DNA cleavage agents4 and azole
containing π-conjugated molecules are prevalent in natural products,
pharmaceuticals and functional materials.5 The direct alkynylation of
azoles with aryl halides have been reported in the presence of Ni6
and Pd7 catalysts. However, the catalytic oxidative coupling or CDC
of arenes and heteroarenes with terminal alkynes through C-H
activation, recently studied with Au,8 Cu,9 Ni,10 Fe11 and Pd12
catalysts as the methodology, has an important advantage; the
formation of molecular hydrogen as a by-product. Although these
reported catalysts afforded comparable yields in C-H alkynylation of
heteroarenes, use of expensive commercial ligands was essential. In
most of the cases, phosphine based ligands, sensitive to air and
moisture, have been used to activate the C-H bond. Moreover, the
catalytic activity of previously reported catalysts is confined to
limited substrates and in some cases, the reactions suffer from harsh
reaction conditions.
Table 1. Optimization studies for the C-H alkynylation of
benzoxazolea
On the other hand, catalytic decarboxylative cross coupling reaction
is a complimentary method to CDC and traditional cross coupling
reactions for the construction of C-C and C-hetero atom bond.13
These
reactions
are
exceptionally
regioselective,
and
environmentally benign processes since carbon dioxide is the only
by-product formed in this reaction. Decarboxylative coupling of aryl
propiolic acids is an attractive area of research because aryl propiolic
acids are usually solids without pungent smell and are easy to
prepare, store, and transport.14 In this context, Lee et al. have
recently developed decarboxylative C-H alkynylation of
benzoxazoles with α, β-ynoic acids using a Pd/dppe catalyst.15 Thus,
the reported processes are important advancements in transition
metal catalyzed cross-coupling reactions; however the study on
development of new active molecular catalyst, which is free from
phosphine ligands in CDC of heteroarenes and decarboxylative cross
coupling reaction, is the topic of investigations and to the best of our
knowledge, phosphine-free metal-N-heterocyclic carbene (NHC)
complex has not been explored so far. The NHC ligands have found
widespread applications in organometallic chemistry due to their
ability to tune the electronic properties of metals, straightforward and
convenient synthesis, less toxic nature and air/moisture stable.
Among the diaminocarbenes16 and other heterocyclic carbenes,17
nucleophilic carbocyclic carbene ligands are less explored in the
catalysis. 18 & 19 In our previous study, we demonstrated the synthesis
and application of anionic/amido carbocyclic carbene palladium (II)
complex (Fig. 1) for room temperature Suzuki coupling of aryl
bromides with boronic acids.19 In continuation to our ongoing work,
we report the catalytic applications of anionic/amido carbocyclic
carbene palladium (II) complex for the C(sp2)−H alkynylation of
azoles here by using two different strategies; one involves cross
a
Reaction conditions: benzoxazole (1a; 0.5 mmol), phenylacetylene
(2a; 1 mmol), Pd Cat. (3 mol%), base (1 mmol) and oxidant (1
b
c
d
mmol) were heated at 85 °C. isolated yields. at 110 °C. with 3
mol% Pd(OAC)2. e with 3 mol% PdCl2. f with 1 mol% Pd Cat.g with
5 mol% Pd Cat. DMF = Dimethylformamide, DMSO = Dimethyl
sulfoxide, NR = No Reaction
Encouraged by this result, the study on screening different solvents,
base, oxidants and reaction parameters, temperature and time was

3
carried out in order to find the optimal reaction conditions. The
could not offer desired products. (Table 2, 3r & 3s).
ACCEPTED MANUSCRIPT
results from these studies are summarized in Table 1. The solvent
screening revealed that the reaction occurred faster in polar aprotic
solvents like DMSO and DMF (Table 1, entries 3 & 4) when
compared to non-polar aprotic solvents like benzene and toluene
(Table 1, entries 1 & 2). The highest yield of desired product (68%,
Table 1, entry 4) was obtained with DMF. With increase in reaction
temperature (110 °C, Table 1, entry 5), the product yield was
decreased to 45% and it may be due to the unwanted
homodimerization of phenyl actelyene. The screening of base
showed that the reaction is sensitive to the nature of base as the
reaction proceeded only when Cs2CO3 base was used (Table 1,
entries 1-5 and 8-17) whereas the reaction did not yield to desired
product with K2CO3 and Na2CO3 (Table 1, entries 6 & 7).
Table 2. Substrate scope for the C-H alkynyation of azoles
with various terminal alkynesa.
In a similar way, study with oxidants revealed that Ag2O is most
suitable oxidant (Table 1, entry 4), while Ag2CO3 and AgOAc gave
poor yields of 3a (Table 1, entries 8 & 9). In addition to above
oxidants, air, TBHP and Cu(OAC)2 were also used as oxidants but
no desired product was obtained (Table 1, entries 10, 11 & 13) while
PhI(OAC)2 afforded trace amount of the desired product (Table 1,
entry 12).
Similarly, Pd(OAC)2 and PdCl2 were used as catalysts to compare
the catalytic efficiency with Pd Cat. but they showed low yield of
desired product (Table 1, entries 14 & 15). The optimal quantity of
the Pd Cat. catalyst required for the maximum conversion was found
to be 3 mol% (Table 1, entries 4, 16 & 17). Thus, among the various
optimization studies listed in Table 1, the most promising result is
shown in entry 4.
With the optimal reaction conditions, the scope of the C-H
alkynylation reaction was examined for several structurally diverse
azoles and terminal alkynes and the results are summarized in Table
2. From Table 2, it can be seen that the reaction of electron rich 1-
ethynyl-4-methylbenzene with benzoxazole proceeded smoothly to
afford the corresponding product 2-(p-tolylethynyl)benzoxazole in
71% yield (Table 2, 3b). In a similar way, disubstituted 1-ethynyl-
2,4-dimethylbenzene also underwent the reaction smoothly to furnish
the desired product in good yields (Table 2, 3c). On the other hand,
the reaction of electron deficient 1-ethynyl-4-fluorobenzene with
benzoxazole
gave
only
47%
yield
of
2-((4-
aReaction conditions: 0.5 mmol of 1, 1mmol of 2, 3mol% Pd
Cat., 1 mmol Ag2O, 1 mmol Cs2CO3 were heated at 85 C in
0
fluorophenyl)ethynyl)benzoxazole (Table 2, 3d). C-H alkynylation
of 6-methylbenzoxazole with phenylacetylene and 1-ethynyl-4-
methylbenzene produced the respective products in good yields
DMF solvent. NR = No Reaction.
(Table 2, 3e
methylbenzoxazole
methoxybenzene,
&
3f). Likewise, C-H alkynylation of 5-
with phenylacetylene, 1-ethynyl-4-
1-ethynyl-4-methylbenzene and 3-
The coupling of benzothiazole proceeded well with phenylacetylene
and 4-methyl phenylacetylene to give corresponding products in
good yields (Table 2, 3t & 3u). Finally, N-benzyl benzamide and N-
benzyl imidazole also reacted well with phenylacetylene producing
the desired C-H alkynylation products in 65% and 41% respectively
(Table 2, 3v and 3w).
To explore further application of Pd Cat. in catalytic process, the
decarboxylative coupling reaction of phenyl propiolic acid with
benzoxazole was studied at 80 °C. Different solvents and oxidants
were tested to find the optimal conditions (See supporting
information for optimization study). Finally, it was observed in
optimization study that DMF and Ag2O are the best solvent and
oxidant in decarboxylative coupling reaction. The scope of
decarboxylative coupling was investigated for a wide variety of
azoles and phenyl propiolic acids using the optimized reaction
conditions and the results are shown in Table 3.
ethynylthiophene also afforded the corresponding products in good
yields (Table 2, 3g, 3h, 3i 3j). The reaction of 5-
&
phenylbenzoxazole with phenylacetylene gave 69% yield of 5-
phenyl-2-(phenylethynyl)benzoxazole (Table 2, 3k). Notably, the
reaction of 5-fluoro benzoxazole alkynylation with phenylacetylene
proceeded smoothly to obtain respective product with 64% yield
(Table 2, 3l) while a significant decrease in the product yields were
observed when 5-chloro benzoxazole and 5-bromo benzoxazole were
used with phenylacetylene (Table 2, 3m & 3n). The electron
deficient substrates like 5-nitrobenzoxazole and methyl benzoxazole-
5-carboxylate reacted with phenylacetylene to give good yields of 5-
nitro-2-(phenylethynyl) benzoxazole and methyl-2-(phenylethynyl)
benzoxazole-5-carboxylate respectively (Table 2, 3o & 3q). Further,
the
reaction
of
5-nitrobenzoxazole
with
1-ethynyl-4-
(trifluoromethoxy) benzene was studied and found moderate yield of
the 5-nitro-2-((4-(trifluoromethoxy) phenyl) ethynyl)- benzoxazole
(Table 2, 3p). Unfortunately, the reactions of benzoxazole with
aliphatic alkynes such as oct-1-yne and prop-2-yn-1-ylcyclohexane,
Phenylpropiolic acid underwent decarboxylative coupling at the
C-2 position of various benzoxazoles to produce corresponding C-H
alkynylation products in good yields (Table 3, 4a-4g). The treatment
of phenylpropiolic acid with benzoxazoles possessing electron

4
Tetrahedron
donating groups like –Ph and –CH at various positions gave good
acid also proceeded smoothly to afford corresponding products in
ACCEPTED MANUSCRIPT
3
yields of the respective products (Table 3, 4b, 4f & 4g).
good yields (Table 2, 4n-4p).
Table 3. Pd Cat. catalyzed decarboxylative alkynylation of
A plausible mechanism for the alkynylation of heteroarenes is
depicted in Scheme 1.12,20 Initially, the deprotonation of azole C(2)-
H takes place by base Cs2CO3 leading to formation of cesium
azolate, which subsequently forms an azolyl complex (A) with Pd
Cat. through transmetallation. Similarly, the deprotonation of
arylacetylene takes place in presence of Cs2CO3 which later attacks
on intermediate A to generate intermediate B. The dimerisation of
arylacetylenes is envisioned during the deprotonation of
arylacetylene and can be minimized by the slow addition of
acetylene to the reaction mixture. The reductive elimination converts
palladium(II) intermediate B to Pd(0) with formation of desired
product 2-alkynylazole. The role of Ag2O is to oxidize Pd(0) back to
Pd(II), which was generated during reductive elimination step.
azoles with aryl propiolic acida
.
Scheme1. Plausible mechanism for the Pd catalyzed oxidative
alkynylation of heteroarenes.
O
R
Pd(0)
Ag(I)
N
Ag(0)
O
where Pd(II)L= Pd Cat.
L = carbene ligand
Pd(II)
L
R
N
B
Pd(II)L
O
L
H
Cs2CO3
Pd(II)
N
N
O
Cs2CO3
Pd(II)L
R
H
A
R
Pd(II)L
Dimer
3. Conclusion
The air and moisture stable palladium-carbene complex was
conveniently prepared from easily available substrates and explored
in the alkynylation of heteroarenes using two different approaches.
In first approach, C2-alkynylated azole was achieved with
phenylacetylenes by cross dehydrogenative reaction and in another
approach, decarboxylative C-H alkynylation of azoles was achieved
with arylpropiolic acids. Both the alkynylation reactions were
performed using low catalyst loading, under relatively mild reaction
conditions and without any use of expensive and air/moisture
sensitive phosphine ligands.
aReaction conditions: 0.5 mmol of 1, 1 mmol of 2, 3 mol% Pd
Cat., 1 mmol silver oxide, were heated at 80 0C in DMF solvent.
4. Experimental section
4.1. General
The potentially labile halides such as fluoro, chloro and bromo
present on benzoxazole also performed well to yield desired product
but their reactivity decreased in order of F>Cl>Br (Table 3, 4c-4e).
Nevertheless, benzoxazoles were alkynylated smoothly with
arylpropiolic acids bearing electron donating groups like –CH3 and –
OCH3 to furnish the corresponding products in good yields (Table 3,
4h & 4i). Interestingly, benzoxazoles bearing electron withdrawing
groups such as nitro and ester at 5th position reacted smoothly with
propiolic acids to afford corresponding products in excellent yields
(Table 3, 4j & 4l) whereas the reaction of benzoxazole with electron
deficient 3-(4-acetylphenyl)propiolic acid afforded low yield of
corresponding product (Table 3, 4m). It is noteworthy that
All commercially available chemicals were used as received. Thin-
layer chromatography plates were visualized by exposure to
ultraviolet light (UV)/Iodine and/or by immersion in an acidic
staining solution of phosphomolybdic acid followed by heating on a
hot plate.1H spectra were obtained on 300 MHz, 500 MHz
spectrometers and 13C NMR spectra were obtained on 75 MHz, and
100 MHz spectrometers. Chemical shifts (δ) are reported in ppm
1
relative to the residual solvent signal (δ = 7.26 for H NMR and δ =
77.0for 13C NMR). Mass spectra were carried out using Quattro LC
triple-quadrupole mass spectrometer (Micromass, Manchester, UK).
High-resolution mass spectra were determined using Quadrupole
decarboxylative
alkynylation
of
benzothiazole,
N-
benzylbenzimidazole and N-benzylimidazole with phenylpropiolic

5
time-of-flight (Q-TOF) mass spectrometer (QSTARXL, Applied
Biosystems/MDS Sciex, Foster city, USA).
1543, 1492, 1445, 1336, 1237, 1096, 944, 806, 746, 618, 574
ACCEPTED MANUSCRIPT
cm-1; m/z: 248(M+H)+; HRMS(ESI) calcd. for C17H14NO
(M+H)+: 248.10699; found: 248.10797.
4.3.4. 2-((4-fluorophenyl)ethynyl)benzo[d]oxazole (3d). White
solid: Rf (5% Ethylacetate/hexane) 0.4; H NMR (300 MHz,
1
4.2. Preparation of Pd Cat.
CDCl3) δ 7.80-7.74 (m, 1H), 7.70-7.63 (m, 2H), 7.59-7.52 (m,
1H), 7.47-7.36 (m, 2H), 7.17-7.08 (m, 2H); 13C NMR (100 MHz,
CDCl3) δ 164.6, 162.6, 150.2, 147.5, 140.9, 134.6, 134.5, 126.3,
125.0, 120.4, 116.3, 116.2, 116.0, 110.5, 92.2, 77.3; IR (KBr) ν
3055, 2923, 2854, 2213, 1643, 1594, 1544, 1444, 1336, 1299,
1130, 937, 833, 740, 528 cm-1; m/z: 238(M+H)+; HRMS(ESI)
calcd. for C15H9FNO (M+H)+: 238.0668; found: 238.0656.
The anionic/amido carbocyclic carbene ligated palladium(II)
complex was prepared according to our previous report.19
4.3. General procedures for the alkynylation of 5-membered
heterocycles
CDC reaction:
4.3.5. 6-methyl-2-(phenylethynyl)benzo[d]oxazole (3e). Yellow
solid: Rf (5% Ethylacetate/hexane) 0.30; H NMR (500 MHz,
To an oven dried 25 mL round bottom flask, palladium complex (7
mg, 3 mol %), cesium carbonate (325 mg, 1 mmol), silver(I) oxide
(229mg, 1 mmol) and azole substrate (0.5 mmol) in 2 mL DMF,
under air, were added. Phenyl acetylene substrate (1 mmol) in DMF
(2 mL) was added to the reaction vessel slowly by dropping funnel
over 2 hours while stirring the reaction mixture on preheated oil bath
at 85 °C. The reaction was allowed to stir for 6 hrs at the same
temperature. The reaction mixture was diluted with EtOAc then
filtered through filter paper. The filtrate was quenched with Ice cold
water and then, aqueous layer was extracted with EtOAc. The
organic phase was washed with NaCl (sat. aq.), dried over Na2SO4,
and concentrated under reduced pressure. The residue was purified
by silica gel column chromatography.
1
CDCl3) δ 7.69-7.59 (m, 3H), 7.48-7.37 (m, 3H), 7.35 (s, 1H),
7.23-7.18 (m, 1H), 2.51 (s, 3H); 13C NMR (100 MHz, CDCl3) δ
150.5, 147.1, 138.8, 136.9, 132.3, 130.1, 128.5, 126.3, 120.3,
119.6, 110.6, 93.0, 77.5, 21.8; IR (KBr) ν 3064, 2923, 2856,
2218, 1600, 1540, 1441, 1376, 1304, 1244, 1112, 950, 753, 597,
525 cm-1; m/z: 234(M+H)+; HRMS(ESI) calcd. for C16 H12NO
(M+H)+: 234.09134; found: 234.09215.
4.3.6. 6-methyl-2-(p-tolylethynyl)benzo[d]oxazole (3f). Yellow
1
solid: Rf (5% Ethylacetate/hexane) 0.40; H NMR (500 MHz,
CDCl3) δ 7.63-7.60 (m, 1H), 7.57-7.53 (m, 2H), 7.34 (s, 1H),
7.23-7.17 (m, 3H), 2.50 (s, 3H), 2.40 (s, 3H); 13C NMR (100
MHz, CDCl3) δ 150.5, 147.3, 140.7, 138.8, 136.8, 132.3, 129.3,
126.2, 119.6, 117.2, 110.6, 93.4, 77.1, 21.8, 21.6; IR (KBr) ν
3030, 2922, 2855, 2216, 1600, 1544, 1448, 1328, 1245, 1106,
942, 806, 599, 527 cm-1; m/z: 248(M+H)+; HRMS(ESI) calcd. for
C17H14NO (M+H)+: 248.10699; found: 248.10813.
Decarboxylative coupling:
To an oven dried 25 mL round bottom flask, palladium complex (7
mg, 3 mol %), silver(I) oxide (229mg, 1 mmol) and aryl propiolic
acid (1 mmol), under air, were added. Azole substrate (0.5 mmol) in
DMF (4 mL) was added to the reaction mixture. The reaction
mixture was stirred at 80 °C for 6-8 hrs. The reaction mixture was
diluted with EtOAc then filtered through filter paper. The filtrate was
quenched with Ice cold water and then, aqueous layer was extracted
with EtOAc. The organic phase was washed with NaCl (sat. aq.),
dried with Na2SO4, and concentrated under reduced pressure. The
residue was purified by silica gel column chromatography.
4.3.7. 5-methyl-2-(phenylethynyl)benzo[d]oxazole (3g). Brown
1
solid: Rf (5% Ethylacetate/hexane) 0.40; H NMR (500 MHz,
CDCl3) δ 7.72-7.62 (m, 2H), 7.54 (s, 1H), 7.50-7.36 (m, 4H),
7.28-7.20 (m, 1H), 2.49 (s, 3H); 13C NMR (100 MHz, CDCl3) δ
148.5, 147.7, 141.2, 134.9, 132.3, 130.2, 128.5, 127.4, 120.2,
120.1, 109.9, 93.1, 77.5, 21.4; IR (KBr) ν 2923, 2856, 1627,
1546, 1472, 1224, 1152, 807, 744 cm-1; m/z: 234(M+H)+;
HRMS(ESI) calcd. for C16H12NO (M+H)+: 234.09134; found:
234.09228.
4.3.1. 2-(phenylethynyl)benzo[d]oxazole (3a). Pale yellow solid;
Rf (5% Ethylacetate/hexane) 0.35; 1H NMR (500 MHz, CDCl3) δ
7.78-7.75 (m, 1H), 7.69-7.65 (m, 2H), 7.57-7.53 (m, 1H), 7.49-
7.37 (m, 5H); 13C NMR (100 MHz, CDCl3) δ 150.2, 147.7,
141.0, 132.4, 130.3, 128.6, 126.2, 125.0, 120.3, 120.1, 110.5,
93.3, 77.4; IR (KBr) ν 3065, 2925, 2854, 2220, 1601, 1543,
1444, 1388, 1134, 939, 751, 681, 521 cm-1; m/z: 220(M+H)+;
HRMS(ESI) calcd. for C15H10NO (M+H)+: 220.07569; found:
220.07628.
4.3.2. 2-(p-tolylethynyl)benzo[d]oxazole (3b). White solid; Rf
(5% Ethylacetate/hexane) 0.38; 1H NMR (500 MHz, CDCl3) δ
7.77-7.74 (m, 1H), 7.58-7.53 (m, 3H), 7.43-7.36 (m, 2H), 7.24-
7.21 (m, 2H), 2.41 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 150.2,
147.8, 140.9, 133.9, 132.3, 129.3, 126.1, 124.9, 117.0, 114.0,
110.5, 93.8, 81.1, 21.7; IR (KBr) ν 2958, 2924, 2854, 2211,
1600, 1546, 1447, 1337, 1258, 1099, 1022, 935, 804, 738, 526
cm-1; m/z: 234(M+H)+; HRMS(ESI) calcd. for C16H12NO
(M+H)+: 234.09134; found: 234.09228.
4.3.8.
2-((4-methoxyphenyl)ethynyl)-5-methylbenzo[d]oxazole
1
(3h). White solid: Rf (10% Ethylacetate/hexane) 0.30; H NMR
(500 MHz, CDCl3) δ 7.63-7.57 (m, 2H), 7.52 (s, 1H),7.40(d, J =
8.4 Hz, 1H), 7.23-7.17 (m, 1H), 6.97-6.88 (m, 2H), 3.86 (s, 3H),
2.48 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 161.1, 148.5, 148.1,
141.3, 134.8, 134.1, 127.2, 120.0, 114.3, 112.2, 109.8, 93.7, 70.5,
55.3, 21.4; IR (KBr) ν 2924, 2856, 2214, 1601, 1547, 1499,
1300, 1252, 1146, 1019, 942, 797, 524 cm-1; m/z: 264(M+H)+;
HRMS(ESI) calcd. for C17H14NO2 (M+H)+: 264.10191; found:
264.10307.
4.3.9. 5-methyl-2-(p-tolylethynyl)benzo[d]oxazole (3i). Light
1
yellow solid: Rf (5% Ethylacetate/hexane) 0.40; H NMR (500
MHz, CDCl3) δ 7.57-7.52 (m, 3H), 7.41 (d, J = 8.3 Hz, 1H),
7.23-7.20 (m, 3H), 2.48 (s, 3H), 2.40 (s, 3H); 13C NMR (100
MHz, CDCl3) δ 148.5, 147.9, 141.2, 140.8, 134.8, 132.3, 129.3,
127.3, 120.0, 117.1, 109.8, 93.6, 77.1, 21.7, 21.4; IR (KBr) ν
3043, 2919, 2211, 1606, 1544, 1474, 1326, 1296, 1145, 944, 804,
699, 523 cm-1; m/z: 248(M+H)+; HRMS(ESI) calcd. for
C17H14NO (M+H)+: 248.10699; found: 248.10628.
4.3.3. 2-((2,4-dimethylphenyl)ethynyl)benzo[d]oxazole (3c).
1
Light yellow solid: Rf (5% Ethylacetate/hexane) 0.37; H NMR
4.3.10. 5-methyl-2-(thiophen-3-ylethynyl)benzo[d]oxazole (3j).
(300 MHz, CDCl3) δ 7.79-7.74 (m, 1H), 7.58-7.53 (m, 1H), 7.45
(s, 1H), 7.43-7.37 (m, 2H), 7.19-7.15 (m, 2H), 2.53 (s, 3H), 2.33
(s, 3H); 13C NMR (100 MHz, CDCl3) δ 150.2, 147.9, 141.1,
138.6, 135.4, 133.2, 131.3, 129.6, 126.1, 124.9, 120.3, 119.7,
110.5, 92.8, 80.7, 20.7, 20.1; IR (KBr) ν 2921, 2855, 2213, 1601,
1
Light yellow solid: Rf (5% Ethylacetate/hexane) 0.35; H NMR
(300 MHz, CDCl3) δ 7.81-7.76 (m, 1H), 7.54(s, 1H), 7.44-7.29
(m, 3H), 7.24-7.19 (m, 1H), 2.48 (s, 3H); 13C NMR (100 MHz,
CDCl3) δ 148.5, 147.7, 141.2, 134.9, 132.4, 129.8, 127.4, 126.0,

6
Tetrahedron
ACCEPTED MANUSCRIPT
120.1, 119.5, 109.8, 88.5, 77.4, 21.4; IR (KBr) ν 3108, 2957,
(500 MHz, CDCl ) δ 8.52-8.44 (m, 1H), 8.20-8.14 (m, 1H), 7.71-
3
2924, 2253, 2215, 1657, 1621, 1584, 1557, 1406, 1281, 1140,
1074, 945, 791, 618, 590 cm-1; m/z: 240(M+H)+; HRMS(ESI)
calcd. for C14H10NOS (M+H)+: 240.04776; found: 240.04889.
4.3.11. 5-phenyl-2-(phenylethynyl)benzo[d]oxazole (3k). White
7.57 (m, 3H), 7.53-7.37 (m, 3H), 3.97(m, 3H); 13C NMR (100
MHz, CDCl3) δ 166.4, 153.5, 153.1, 141.1, 132.5, 130.5, 128.6,
128.0, 127.5, 122.7 122.3, 119.8, 110.8, 110.4, 94.3, 77.2, 52.3;
IR (KBr) ν 3005, 2923, 2220, 1721, 1613, 1550, 1429, 1299,
1208, 1080, 967, 751, 684, 525 cm-1; m/z: 278(M+H)+;
HRMS(ESI) calcd. for C17H12NO3 (M+H)+: 278.08117; found:
278.08050.
1
solid: Rf (5% Ethylacetate/hexane) 0.37; H NMR (500 MHz,
CDCl3) δ 8.31-8.27 (m, 1H), 7.99-7.93 (m, 1H), 7.70-7.58 (m,
5H), 7.57-7.54 (m, 1H), 7.50-7.36 (m, 5H); 13C NMR (100 MHz,
CDCl3) δ 149.8, 148.2, 141.6, 140.6, 138.9, 132.4, 130.3, 128.8,
128.6, 127.4(2), 125.9, 120.1, 118.7, 110.5, 93.6, 77.4; IR (KBr)
ν 3060, 2923, 2218, 1655, 1595, 1539, 1446, 1301, 1257, 1138,
1110, 939, 757, 691, 523 cm-1; m/z: 296(M+H)+; HRMS(ESI)
calcd. for C21H14NO (M+H)+: 296.10699; found: 296.10660.
4.3.12. 5-fluoro-2-(phenylethynyl)benzo[d]oxazole (3l). Yellow
4.3.18. 2-(phenylethynyl)benzo[d]thiazole (3t). Yellow solid: Rf
(5% Ethylacetate/hexane) 0.35; 1H NMR (300 MHz, CDCl3) δ
8.13-8.06 (m, 1H), 7.92-7.85 (m, 1H), 7.70-7.60 (m, 2H), 7.56-
7.40 (m, 5H); 13C NMR (100 MHz, CDCl3) δ 152.9, 148.5,
135.3, 132.1, 129.8, 128.5, 126.6, 126.1, 123.5, 121.2, 120.9,
95.8, 82.6; IR (KBr) ν 2923, 2855, 2216, 1606, 1544, 1454,
1328, 1254, 1106, 942, 812, 529 cm-1; m/z: 236(M+H)+;
HRMS(ESI) calcd. for C15H10NS (M+H)+: 236.05285; found:
236.05404.
1
solid: Rf (5% Ethylacetate/hexane) 0.45; H NMR (500 MHz,
CDCl3) δ 7.70-7.64 (m, 2H), 7.51-7.40 (m, 5H), 7.19-7.12 (m,
1H); 13C NMR (100 MHz, CDCl3) δ 161.2, 159.3, 149.2, 146.5,
141.8, 132.4, 130.5, 128.6, 119.9, 114.2, 114.0, 110.9, 110.8,
106.6, 106.4, 93.9, 77.1, 70.5; IR (KBr) ν 3056, 2926, 2856,
2212, 1598, 1542, 1469, 1438, 1380, 1267, 1129, 952, 855, 756,
686, 530 cm-1; m/z: 238(M+H)+; HRMS(ESI) calcd. for
C15H9FNO (M+H)+: 238.06627; found: 238.06551.
4.3.19. 2-(p-tolylethynyl)benzo[d]thiazole (3u). Yellow solid: Rf
(5% Ethylacetate/hexane) 0.40; H NMR (300 MHz, CDCl3) δ
1
8.07 (d, J = 8.6 Hz, 1H), 7.87 (d, J = 8.6 Hz, 1H), 7.57-7.42 (m,
4H), 7.24-7.18 (m, 2H), 2.40 (s, 3H); 13C NMR (100 MHz,
CDCl3) δ 152.9, 148.8, 140.3, 135.2, 132.0, 129.3, 126.6, 126.0,
123.4, 121.2, 117.8, 96.3, 82.2, 21.6; IR (KBr) ν 3058, 3026,
2923, 2853, 2201, 1606, 1514, 1472, 1311, 1096, 1051, 938, 813,
755, 521 cm-1; m/z: 250(M+H)+; HRMS(ESI) calcd. for
C16H12NS (M+H)+: 250.06850; found: 250.06796.
4.3.13. 5-chloro-2-(phenylethynyl)benzo[d]oxazole (3m). Yellow
1
solid: Rf (5% Ethylacetate/hexane) 0.50; H NMR (500 MHz,
CDCl3) δ 7.75 (s, 1H), 7.70-7.64 (m, 2H), 7.50-7.36 (m, 5H); 13
C
NMR (100 MHz, CDCl3) δ 148.9, 148.8, 142.1, 132.5, 130.6,
130.5, 128.6, 126.6, 120.2, 119.9, 111.3, 94.1, 77.0; IR (KBr) ν
3089, 2924, 2856, 2215, 1656, 1538, 1438, 1294, 1250, 1137,
941, 810, 748, 680, 590, 525 cm-1; m/z: 254(M+H)+; HRMS(ESI)
calcd. for C15H9ClNO (M+H)+: 254.03672; found: 254.03643.
4.3.14. 5-bromo-2-(phenylethynyl)benzo[d]oxazole (3n). Brown
4.3.20. 1-benzyl-2-(phenylethynyl)-1H-benzo[d]imidazole (3v).
White solid: Rf (30% Ethylacetate/hexane) 0.30; H NMR (500
1
MHz, CDCl3) δ 7.79 (d, J = 7.0 Hz, 1H), 7.59(d, J = 6.7 Hz, 2H),
7.43-7.27 (m, 11H), 5.55 (s, 2H); 13C NMR (100 MHz, CDCl3) δ
143.2, 137.5, 135.8, 134.1, 132.0, 129.7, 128.9, 128.5, 128.0,
127.0, 124.0, 123.0, 121.0, 120.3, 110.1, 95.0, 78.9, 48.4; IR
(KBr) ν 3028, 2923, 2213, 1602, 1495, 1444, 1395, 1275, 1103,
749, 722, 686, 450 cm-1; m/z: 309(M+H)+; HRMS(ESI) calcd. for
C22H16N2 (M+H)+: 309.13863; found: 309.13822.
1
solid: Rf (5% Ethylacetate/hexane) 0.55; H NMR (500 MHz,
CDCl3) δ 7.90 (d, J = 1.8 Hz, 1H ), 7.70-7.65 (m, 2H), 7.53 (dd, J
= 8.6, 1.8 Hz, 1H), 7.50-7.46 (m, 1H), 7.45-7.40 (m, 3H); 13C
NMR (100 MHz, CDCl3) δ 149.2, 148.7, 142.5, 132.5, 130.5,
129.3, 128.6, 123.2, 119.8, 117.8, 111.7, 94.2; IR (KBr) ν 3085,
2924, 2853, 2243, 2215, 1647, 1599, 1539, 1443, 1294, 1251,
1137, 941, 854, 809, 748, 680, 528 cm-1; m/z: 298(M+2)+;
HRMS(ESI) calcd. for C15H9BrNO (M+H)+: 297.98620; found:
297.98580.
4.3.21. 1-benzyl-2-(phenylethynyl)-1H-imidazole (3w). Light
brown solid: Rf (60% Ethylacetate/hexane) 0.30; H NMR (500
1
MHz, CDCl3) δ 7.55-7.50 (m, 2H), 7.39-7.33 (m, 6H), 7.26-7.22
(m, 2H), 7.14 (s, 1H), 6.93 (s, 1H), 5.28 (s, 2H); 13C NMR (100
MHz, CDCl3) δ 136.0, 132.4, 131.6, 129.9, 129.0, 128.9, 128.3,
128.2, 127.4, 121.7, 120.4, 93.0, 78.5, 50.6; IR (KBr) ν 3062,
3031, 2925, 2853, 2219, 1679, 1648, 1600, 1517, 1458, 1277,
1119, 1073, 918, 756, 694, 524 cm-1; m/z: 259(M+H)+;
HRMS(ESI) calcd. for C18H15N2 (M+H)+: 259.1235; found:
259.1223.
4.3.15. 5-nitro-2-(phenylethynyl)benzo[d]oxazole (3o). Orange
solid; Rf (10% Ethylacetate/hexane) 0.40; H NMR (500 MHz,
1
CDCl3) δ 8.66 (d, J = 2.2 Hz, 1H ), 8.41-8.37 (m, 1H), 7.71-7.65
(m, 3H), 7.54-7.49 (m, 1H), 7.47-7.43(m, 2H); 13C NMR (100
MHz, CDCl3) δ 153.6, 150.4, 145.6, 141.4, 132.6, 130.9, 128.7,
122.0, 119.4, 116.6, 110.8, 95.5, 76.5, 70.5; IR (KBr) ν 3106,
3069, 2854, 2217, 1608, 1525, 1436, 1347, 1108, 947, 758, 688,
529 cm-1; m/z: 265(M+H)+; HRMS(ESI) calcd. for C15H9O3N2
(M+H)+: 265.06077; found: 265.06047.
4.3.22. 2-(naphthalen-1-ylethynyl)-5-nitrobenzo[d]oxazole (4k).
Greenish yellow solid: Rf (10% Ethylacetate/hexane) 0.35; 1H
NMR (500 MHz, CDCl3) δ 8.69 (d, J = 2.2 Hz, 1H), 8.47-8.37
(m, 2H), 8.04-7.91 (m, 3H), 7.74-7.67 (m, 2H), 7.64-7.59 (m,
1H), 7.56-7.52 (m, 1H); 13C NMR (100 MHz, CDCl3) δ 153.7,
150.5, 145.7, 141.5, 133.2, 133.0, 132.8, 131.7, 128.6, 127.8,
127.0, 125.5, 125.1, 122.1, 117.0, 116.6; 110.8, 94.2, 81.1; IR
(KBr) ν 3102, 3055, 2923, 2853, 2211, 1609, 1531, 1345, 1146,
774, 691, 564 cm-1; m/z: 315(M+H)+; HRMS(ESI) calcd. for
C19H11O3 N2 (M+H)+: 315.07642; found: 315.07620.
4.3.16.
5-nitro-2-((4-
(trifluoromethoxy)phenyl)ethynyl)benzo[d]oxazole (3p). Dark
brown solid: Rf (5% Ethylacetate/hexane) 0.40; 1H NMR (500
MHz, CDCl3) δ 8.67 (d, J = 2.2 Hz, 1H), 8.37-8.31 (m, 2H),
8.08-8.00 (m, 1H), 7.71 (d, J = 8.8 Hz, 1H), 7.41 (d, J = 8.0 Hz,
1H), 7.35-7.28 (m, 1H); 13C NMR (100 MHz, CDCl3) δ 164.6,
154.2, 152.2, 145.5, 142.4, 133.0, 129.8, 129.6, 127.1, 124.7,
124.4, 121.6, 121.3, 121.1, 120.8, 116.4, 110.8; IR (KBr) ν 3109,
2925, 2855, 2426, 2198, 1622, 1539, 1501, 1461, 1349, 1259,
1167, 920, 829, 689, 600, 509 cm-1; m/z: 349(M+H)+;
HRMS(ESI) calcd. for C16H8F3N2O4 (M+H)+: 349.04307 found:
349.04335.
4.3.23. 1-(4-(benzo[d]oxazol-2-ylethynyl)phenyl)ethanone (4m).
Yellow solid: Rf (10% Ethylacetate/hexane) 0.50; H NMR (500
MHz, CDCl3) δ 7.93 (d, J = 8.5 Hz, 2H), 7.73 (d, J = 7.9 Hz,
2H), 7.55-7.47 (m, 4H), 3.65 (s, 3H); IR (KBr) ν 2925, 2854,
1736, 1686, 1627, 1443, 1379, 1243, 1122, 943, 744, 542 cm-1;
m/z: 262(M+H)+;
1
4.3.17. methyl 2-(phenylethynyl)benzo[d]oxazole-5-carboxylate
1
(3q). white solid: Rf (10% Ethylacetate/hexane) 0.35; H NMR

7
18. (a) Yao, Q.; Zabawa, M.; Woo, J.; Zheng, C. J. Am. Chem. Soc.
Acknowledgments
ACCEPTED MANUSCRIPT
2007, 129, 3088-3089; (b) Herrmann, W. A.; fele, K.; Schneider,
S. K.; Herdtweck, E.; Hoffmann, S. D. Angew. Chem. Int. Ed.
2006, 45, 3859-3862; (c) fele, K. O.; Tosh, E.; Taubmann, C.;
Herrmann, W. A. Chem. Rev. 2009, 109, 3408-3444.
19. Kantam, M. L.; Parsharamulu, T.; Likhar P. R.; Srinivas, P. J.
Organomet. Chem. 2013, 729, 9-13.
T.P.R thanks UGC, New Delhi for the award of senior research
fellowship.
References and notes
20. Wei, Y.; Zhao, H.; Kan, J.; Su, W.; Hong, M. J. Am. Chem. Soc.
2010, 132, 2522-2523.
1. (a) Kakiuchi, F.; Chatani, N. Adv. Synth. Catal. 2003, 345, 1077-
1101; (b) Miura, M.; Satoh, T. Top. Organomet. Chem. 2005, 14,
55-83; (c) Alberico, D.; Scott, M. E.; Lautens, M. Chem. Rev.
2007, 107, 174-238; (d) Satoh, T.; Miura, M. Chem. Lett. 2007,
36, 200-205; (e) Park, Y. J.; Park, J.-W.; Jun, C.-H. Acc. Chem.
Res. 2008, 41, 222-234; (f) Lewis, L. C.; Bergman, R. G.; Ellman,
J. A. Acc. Chem. Res. 2008, 41, 1013-1025; (g) Kakiuchi, F.;
Kochi, T. Synthesis, 2008, 3013-3039.
2. (a) Shilov, A. E.; Shulpin, G. B. Chem. Rev. 1997, 97, 2879-2932;
(b) Daugulis, O.; Do, H.-Q. Shabashov, D. Acc. Chem. Res. 2009,
42, 1074-1086; (c) Giri, R.; Shi, B.-F.; Engle, K. M.; Maugel, N.;
Yu, J.-Q. Chem. Soc. Rev. 2009, 38, 3242-3272; (d) Sun, C.-L.;
Li, B.-J.; Shi, Z.-J. Chem. Commun. 2010, 46, 677-685; (e)
Gunay, A.; Theopold, K. H. Chem. Rev. 2010, 110, 1060-1081; (f)
Hwang, S. J.; Cho, S. H.; Chang, S. J. Am. Chem. Soc. 2008, 130,
16158-16159; (g) Park, E. J.; Kim, S. H.; Chang, S. J. Am. Chem.
Soc. 2008, 130, 17268-17269; (h) Cho, S. H.; Kim, J. Y.; Lee, S.
Y.; Chang, S. Angew. Chem., Int. Ed. 2009, 48, 9127-9130; (i)
Kim, J. Y.; Cho, S. H.; Joseph J.; Chang, S.; Angew. Chem., Int.
Ed. 2010, 49, 9899-9903; (j) Kim, J.; Chang, S. J. Am. Chem. Soc.
2010, 132, 10272-10274.
3. lewis, J. C.; Bergman, R. G.; Ellman. J. A. Acc. Chem. Res. 2008,
41, 1013-1025.
4. Kumar, D.; David, W. M.; Kerwin, S. M. Bioorg. Med. Chem.
Lett. 2001, 11, 2971-2974.
5. (a) Hassan, J.; Sevignon, M.; Gozzi, C.; Schulz, E.; Lemaire, M.
Chem. Rev. 2002, 102, 1359-1470; (b) Corbet, J.-P; Mignani, G.
Chem. Rev. 2006, 106, 2651-2710.
6. Matsuyama, N.; Hirano, K.; Satoh, T.; Miura, M. Org. Lett. 2009,
11, 4156-4159.
7. Kim, S. H.; Chang, S. Org. Lett. 2010, 12, 1868-1871.
8. Haro, T.; Nevado, C.; J. Am. Chem. Soc. 2010, 132, 1512-1513.
9. Wei, Y.; Zhao, H.; Kan, J.; Su, W.; Hong, M. J. Am. Chem. Soc.
2010, 132, 2522-2523.
10. Matsuyama, N.; Kitahara, M.; Hirano, K.; Satoh, T.; Miura, M.
Org. Lett., 2010, 12, 2358-2361.
11. Patil, S. S.; Jadhav, R. P.; Patil, S. V.; Bobade. V. D. Tetrahedron
Lett. 2011, 52, 5617-5619.
12. (a) Hwan, S.; Yoon, K. J.; Chan, S. Org. Lett. 2011, 13, 1474-
1477; (b) Shibahara, F.; Dohke, Y.; Murai, T. J. Org. Chem.,
2012, 77, 5381-5388.
13. (a) Weaver, J. D.; Recio, A.; Grenning A. J.; Tunge, J. A. Chem.
Rev. 2011, 111, 1846-1913; (b) Rodríguez, N.; Gooßen, L. J.
Chem. Soc. Rev. 2011, 40, 5030-5048; (c) Hu, P.; Shang, Y.; Su,
W. Angew. Chem., Int. Ed. 2012, 51, 5945-5949; (d) Song, B.;
Knauber, T.; Gooßen, L. J. Angew. Chem., Int. Ed., 2013, 52,
2954-2958; (e) Bhadra, S.; Dzik, W. I.; Gooßen, L. J. J. Am.
Chem. Soc. 2012, 134, 9938-9941; (f) Shard, A.; Sharma, N.;
Bharti, R.; Dadhwal, S.; Kumar, R.; Sinha, A. K. Angew. Chem.,
Int. Ed. 2012, 51, 12250-12253; (g) Yin, F.; Wang, Z. T.; Li, Z.
D.; Li, C. Z. J. Am. Chem. Soc. 2012, 134, 10401-10404.
14. (a) Hajbi, Y.; Neagoie, C.; Biannic, B.; Chilloux, A.; Vedrenne,
E.; Baldeyrou, B.; Bailly, C.; Merour, J.-Y.; Rosca, S.; Routier, S.;
Lansiaux, A. Eur. J. Med. Chem. 2010, 45, 5428-5437; (b) Yu, D.;
Zhang, Y. Green Chem. 2011, 13, 1275-1279; (c) Arndt, M.;
Risto, E.; Krause, T.; Goossen, L. J. ChemCatChem, 2012, 4, 484-
487; (d) Yu, D.; Tan, M.-X.; Zhang, Y. Adv. Synth. Catal. 2012,
354, 969-974 (e) Park, K.; You, J.-M.; Jeon, S.; Lee, S. Eur. J.
Org. Chem. 2013, 1973-1978.
15. Kim, J.; Kang, D.; Yoo, E. J.; Lee, P. H. Eur. J. Org. Chem. 2013,
7902-7906.
16. (a) Owusu, M. O.; Handa, S.; Slaughter, L. M. Appl.
Organometal. Chem. 2012, 26, 712-717; (b) Tskhovrebov, A. G.;
Luzyanin, K. V.; Dolgushin, F. M.; Fatima, M.; Silva, C. G.;
Pombeiro, A. J. L.; Kukushkin, V. Y. Organometallics, 2011, 30,
3362-3370; (c) Rosen, E. L.; Sung, D. H.; Chen, Z.; Lynch, V. M.;
Bielawski, C. W. Organometallics, 2010, 29, 250-256.
17. (a) Guo, C.; Schedler, M.; Daniliuc, C. G.; Glorius, F. Angew.
Chem. Int. Ed. 2014, 53, 10232-10236; (b) John, A.; Ghosh, P.
Dalton Trans., 2010, 39, 7183-7206; (c) Ikota, H.; Ishida, T.;
Tsukano, C.; Takemoto, Y. Chem. Commun. 2014, 50, 8871-8874.

ACCEPTED MANUSCRIPT
Supporting Information
Dehydrogenative and Decarboxylative C-H Alkynylation of
Heteroarenes catalyzed by Pd(II) Carbene Complex
T. Parsharamulu, P. Vishnuvardhan Reddy, Pravin R. Likhar* and M. Lakshmi Kantam*
Inorganic and Physical Chemistry Division, Indian Institute of chemical Technology, Hyderabad-
500607, India. Fax: +91-040-27160921; Tel: +91-040-27193030.email: mlakshmi@iict.res.in;
plikhar@iict.res.in
List of Contents
Page No
1. Optimization study for the
decarboxylative coupling reaction
2
2. 1H and 13C NMR spectra of the compounds
3 - 25
1

ACCEPTED MANUSCRIPT
Table 1: Optimization studies for the decarboxylative alkynylation of benzoxazolea.
O
N
O
N
O
Pd Cat.
Oxidant, solvent,
under air, -CO2
HO
Time(h)
10
yield(%)b
54
entry
oxidant
solvent
1
Toluene
Ag2O
2
3
4
benzene
10
15
8
62
Ag2O
Ag2O
Ag2O
Methanol
trace
74
DMF
DMF
DMF
10
45
5
6
AgOAc
air
trace
15
7
8
9
Cu(OAc)2
Ag2O
15
15
NR
65c
DMF
DMF
DMF
Ag2O
10
61d
a
Reaction scale: benzoxazole (0.5 mmol), phenylpropiolicacid(1 mmol), Pd Cat. (3 mol%),
0
b
c
0
d
oxidant (1 mmol) at 80 C. isolated yields. at 70 C. 1 mol% Pd Cat. DMF = Dimethyl
formamide, NR = No Reaction.
2

ACCEPTED MANUSCRIPT
1H &13C NMR spectra of 3a
3

ACCEPTED MANUSCRIPT
1H &13C NMR spectra of 3b
4

ACCEPTED MANUSCRIPT
1H &13C NMR spectra of 3c
5

ACCEPTED MANUSCRIPT
1H &13C NMR spectra of 3d
6

ACCEPTED MANUSCRIPT
1H &13C NMR spectra of 3e
7

ACCEPTED MANUSCRIPT
1H &13C NMR spectra of 3f
8

ACCEPTED MANUSCRIPT
1H &13C NMR spectra of 3g
9

ACCEPTED MANUSCRIPT
1H &13C NMR spectra of 3h
10

ACCEPTED MANUSCRIPT
1H &13C NMR spectra of 3i
11

ACCEPTED MANUSCRIPT
1H &13C NMR spectra of 3j
12

ACCEPTED MANUSCRIPT
1H &13C NMR spectra of 3k
13

ACCEPTED MANUSCRIPT
1H &13C NMR spectra of 3l
14

ACCEPTED MANUSCRIPT
1H &13C NMR spectra of 3m
15

ACCEPTED MANUSCRIPT
1H &13C NMR spectra of 3n
16

ACCEPTED MANUSCRIPT
1H &13C NMR spectra of 3o
17

ACCEPTED MANUSCRIPT
1H &13C NMR spectra of 3p
18

ACCEPTED MANUSCRIPT
1H &13C NMR spectra of 3q
.
19

ACCEPTED MANUSCRIPT
1H &13C NMR spectra of 3t
20

ACCEPTED MANUSCRIPT
1H &13C NMR spectra of 3u
21