Microwave-Assisted Condensation of Benzylic Alcohols and Alkynes Promoted by Zinc Halides: Concise Access to Alkenyl Halides

Article abstract of DOI:10.1002/ejoc.202100779

A simple Lewis acid-mediated route for the synthesis of alkenyl halides are described under microwave-assisted conditions. The reaction proceeds through the condensation between secondary alcohols and terminal acetylenes and regioselective hydrohalogenati

Full text of DOI:10.1002/ejoc.202100779

European Journal of Organic Chemistry
Accepted Article
Accepted Article
Title: Microwave Assisted Condensation of Benzylic Alcohols and
Alkynes Promoted by Zinc Halides: Concise Access to Alkenyl
Halides
Authors: Poulomi Nandi, Komal Goel, Chinnabattigalla Sreenivasulu,
and Gedu Satyanarayana
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To be cited as: Eur. J. Org. Chem. 10.1002/ejoc.202100779
Link to VoR: https://doi.org/10.1002/ejoc.202100779
01/2020

10.1002/ejoc.202100779
European Journal of Organic Chemistry
FULL PAPER
Microwave-Assisted Condensation of Benzylic Alcohols and
Alkynes Promoted by Zinc Halides: Concise Access to Alkenyl
Halides
Poulomi Nandi, Komal Goel, Chinnabattigalla Sreenivasulu and Gedu Satyanarayana*[a]
Dedication ((optional))
[a]
Ms. Poulomi Nandi, Ms. Komal Goel, Mr. Chinnabattigalla Sreenivasulu and Prof. Gedu Satyanarayana
Department of Chemistry
Indian Institute of Technology, Hyderabad
Kandi – 502 285, Sangareddy, Telangana, INDIA, Phone: (040) 2301 6251; Fax: (040) 2301 6003/32
E-mail: gvsatya@chy.iith.ac.in
https://sites.google.com/site/gsresearchgrouphomepage/home
Supporting information for this article is given via a link at the end of the document.((Please delete this text if not appropriate))
Abstract: A simple Lewis acid-mediated route for the synthesis of
alkenyl halides is described under microwave-assisted conditions.
The reaction proceeds through the condensation between sec-
synthesizing alkenyl halides was based on hydro-halides (HX)
and alkynes.[18,19] Most of the methods have been developed
from ketone and aldehydes in the presence of halogenating
reagents (such as phosphorous pentachloride, phosphorous
oxychloride, etc.).[20,21] Alternatively, these alkenyl halides are
prepared by the reaction of alcohols and vinyl boron dihalides
in the presence of nBuLi (Figure 1c).[22] Also, there are some
of the relevant processes wherein terminal acetylenes and
benzylic alcohols were employed in the presence of a strong
Lewis to furnish alkenyl halides (Figure 1).[23–26] Nevertheless,
the synthesis of alkenyl halides via the construction of a new
CC bond from terminal alkynes and benzylic alcohols is
scarcely explored. Therefore, there is enough scope and room
to explore and develop new and efficient methods for alkenyl
halides synthesis.
alcohols
and
terminal
acetylenes,
and
regioselective
hydrohalogenation across the triple bond in the presence of simple
and commercially available zinc halides. Unlike earlier reports, this
methodology is successfully exemplified with three halide sources. As
a result, a diverse range of alkenyl halide products has been
accomplished. Further, indenes were obtained as the end products
when tert-alcohols and arylacetylenes were used, wherein, the
Thorpe–Ingold, as well as electronic effects, would be dominant.
Furthermore, when an electron-rich arylacetylene was employed,
directed to yield carbonyl products.
Introduction
Alkenyl halides are of great importance since they
can be served as multifaceted synthons in the synthesis of
numerous natural products, pharmaceutical compounds,
polymers, etc.[1–9] Furthermore, they are considered as key
preliminary materials for constructing C–C, C–N, and C–O
The utilization of benzylic alcohols as an electrophilic
synthetic precursor is quite useful as they are structurally
diverse and can be instantly accessible by simple sodium
borohydride reduction from acetophenone/benzophenone
derivatives. However, direct replacement of hydroxyl moiety
of benzylic alcohols is a difficult task. Traditional methods for
substitution of hydroxyl functionality are centered on the
conversion of the hydroxyl group into a good leaving group
(i.e., to the corresponding halides, esters, etc.) or usage of
stringent acidic conditions or transition-metal based catalysts,
such as palladium, ruthenium, copper, gold, and rhodium. [27–
bonds
using
transition-metal
catalyzed
coupling
transformations,
such as, Heck,
Suzuki–Miyaura,
Sonogashira, Negishi, Stille, and Buchwald–Hartwig
reactions.[10–17] So, the inevitability of these compounds as
chemical feedstock is indispensable. However, unfortunately,
the accessibility of alkenyl halides is near to the ground and is
often expensive. Consequently, the accomplishment of such
compounds is still stimulating and draws ample attention from
the synthetic community. The well-known classical method for
32]
Though metal-catalyzed CC bond creation in organic
synthesis has always been an enthralling research topic,
1
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10.1002/ejoc.202100779
European Journal of Organic Chemistry
FULL PAPER
replacing such extravagant metals with inexpensive reagents
like mild, green, and nontoxic Lewis acids is a requisite and
advantageous alternative in the development of new methods.
Besides, the use of microwave energy instead of
traditional heating often affords the products in good yields for
short period compared to the reaction by classical synthetic
methods. Therefore, microwave-assisted organic synthesis is
preferred over conventional methods. Thus, when compared
with earlier reports on this similar concept, the present method
is a simple, efficient route to synthesize a variety of products,
namely, alkenyl halides, indenes, and ketones under
microwave-assisted conditions.
Undoubtedly,
from an economic standpoint and
straightforwardness, the simple Lewis acid induced strategies
are beneficial; moreover, it is also desirable to develop new
methods using milder reaction conditions. The development
and implementation of such simplified chemical processes are
very much essential for organic synthesis.
As far as we know, there are only a couple of reports
are known in the literature on achieving alkenyl iodides using
benzylic alcohols and terminal acetylenes in the presence of
powdered iron and iodinating reagents (i.e., I2 and NaI).[33]
Herein, our main intention was to accomplish such alkenyl
halides by making use of a simple reagent, which could play
a dual role as a Lewis acid and as well a halide source. Also,
specifically, it was intended to develop a one-pot microwave-
assisted method for the formation of alkenyl halides by direct
condensation of benzylic alcohols and terminal alkynes. This
sort of chemical process is attractive and eco-friendly as water
is the sole by-product. As a continuation to our research
interests in emerging one-pot domino methods to synthesize
carbo-/heterocyclic
compounds,
recently,
we
have
established methods based on an efficient one-pot synthesis
of benzofurans driven by a simple Lewis acid ZnCl2.[34]
Subsequently, a one-pot process for the construction of
chromenes induced by ZnCl2 has also been achieved.[35]
Herein, we present ZnI2 mediated one-pot synthesis of alkenyl
iodides, in which, interestingly, ZnI2 fulfilled the role of Lewis
acid and the halogenating agent. Delightfully, the strategy has
been applied to the accomplishment of alkenyl bromides and
chlorides in the presence of ZnBr2 and ZnCl2, respectively. In
addition, it was noticed that the reaction did not impede after
the alkenyl halide instead progressed to the ketone when the
aromatic ring of the terminal acetylene was sufficiently
electron-rich. This led us to explore the scope of forming C–C
and C–O bonds to generate aryl ketones with 100% atom
efficiency. Moreover, it was demonstrated that the Thorpe–
Ingold, as well as electronic effects, would be preferred and
furnished indenes as the end products when tert-alcohols and
aryl acetylenes were used as the starting materials.
Figure 1: A comparison chart of earlier report vs the present study.
Results and Discussion
In continuation to our previous research work on
Lewis acids mediated transformations; we envisioned alkenyl
halides could be achieved from secondary benzylic alcohols
and terminal acetylenes in the presence of a suitable Lewis
acid that can act as a promoter as well as the halogenating
agent. To initiate the research work, different substituted
benzylic alcohols 1a-i were synthesized either by carrying out
2
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10.1002/ejoc.202100779
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Grignard reaction of substituted benzaldehyde or reducing the
substituted aryl ketones by sodium borohydride.
very good yield (88%, E:Z = 84:16 ratio, Table 1, entry 6). Next,
in attempts towards increasing yield, two reactions were
performed using 0.5 equiv and 1.5 equiv of zinc iodide.
However, in the case of 0.5 equiv of ZnI2 (Table 1, entry 7),
the reaction was sluggish and led to the formation of homo-
condensed ether intermediate 1a‘ along with the desired
product 3aa. Conversely, usage of 1.5 equiv of ZnI2 and
reaction time for 20 min, could not improve the yield (87%, E:Z
= 80:20 ratio, Table 1, entry 8). Switching the Lewis acid from
ZnI2 to SnCl2·2H2O has not shown any positive effect in
increasing the yield and afforded 3aa only in 42% yield (Table
1, entry 9). Whereas the reaction with SnCl2 H2O (20 mol%)
and NaI (1 equiv) afforded a mixture of alkenyl iodides 3aa
and alkenyl chlorides with less selectivity and very less yield
34% (Table 1, entry 10). Further, the reaction with ZnI2 (10
mol%) and NaI (1 equiv) resulted in the formation of alkenyl
iodide product 3aa with less selectivity and very less yield 45%
(Table 1, entry 11). On the other hand, the reaction at low
temperature (80 C) with 0.5 equiv of ZnI2 for 20 min, furnished
the homo-condensed ether intermediate 1a‘ as the major
product (63%) along with the usual alkenyl iodide E/Z mixture
3aa in 18% yield (Table 1, entry 12).
With the starting materials in hand, next, it was
planned to optimize the reaction conditions to synthesize
alkenyl halides under microwave-assisted conditions. In this
context, diphenylmethanol 1a and phenylacetylene 2a have
been chosen as the prototypical substrates. The reaction was
explored under different conditions, such as varying amounts
of ZnI2, with various solvents, at different temperatures and
reaction times, and the results are as detailed in Table 1. To
begin with, at first one equivalent of ZnI2 was used for
promoting the reaction in acetonitrile solvent. As anticipated,
a moderate yield of 50% of the desired alkenyl iodide 3aa was
formed as a mixture of geometrical isomers (E:Z = 75:25), in
acetonitrile at 100 °C for 20 min under 300 microwave
irradiation (Table 1, entry 1). The result is similar when the
reaction was executed in 1,2-dichloroethane (1,2-DCE)
solvent at 80 °C (Table 1, entry 2). However, at a slightly
raised temperature (100 °C) in the same solvent (1,2-DCE),
furnished the product 3aa (E:Z = 84:16) in 85% (Table 1, entry
3). Also, altering the solvent from 1,2-DCE to 1,4-dioxane,
afforded the product 3aa in moderate yield of 52% [(E:Z =
70:30), Table 1, entry 4]. While DMF was turned out to be a
bad choice and could not promote the reaction (Table 1, entry
5). Gratifying, the reaction at
a further slightly high
temperature at 120 °C in 1,2-DCE, lead to the product 3aa in
Table 1: Optimization study to access (E/Z)-(3-iodoprop-2-ene-1,1,3-triyl)tribenzene 3aaa,b,c.d.e
3
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European Journal of Organic Chemistry
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Entry
Lewis Acid
(equiv)
ZnI2 (1)
ZnI2 (1)
ZnI2 (1)
ZnI2 (1)
Solvent
(1 mL)
Temp
(°C)
100
80
100
100
100
120
120
120
100
120
120
80
Time
(min)
Yieldb (%)
E:Zc ratio
3aa
50
55
85
52
--- d
88
---e
87
42
34
45
18
1a‘
---
---
---
---
---
---
47
---
---
---
---
63
1
2
3
4
5
ACN
1,2-DCE
1,2-DCE
1,4 Dioxane
DMF
1,2-DCE
1,2-DCE
1,2-DCE
1,2-DCE
1,2-DCE
1,2-DCE
1,2-DCE
20
20
20
20
20
20
20
20
20
20
20
20
75:25
79:21
84:16
70:30
---
84:16
---
80:20
80:20
---h
75:25

ZnI2 (1)
ZnI2 (1)
6
7
8
9
10
11
12
ZnI2 (0.5)
ZnI2 (1.5)
SnCl22H2O (1)f
SnCl22H2O (0.2)g
ZnI2 (0.2)g
ZnI2 (0.5)
aReaction condition: diphenylmethanol 1a (92 mg, 0.5 mmol), ethynylbenzene 2a (51 mg, 0.5 mmol) under microwave irradiation (300, closed
vessel). bIsolated yields of chromatographically pure E/Z mixture product 3aa. cThe E/Z ratio calculated by 1H NMR analysis of 3aa. dStarting
materials were recovered. eA mixture of homo-condensed ether 1a‘ and 3aa were formed. fAlkenyl chlorides (E/Z) were formed. gNaI (1 equiv)
was used. hA mixture of both alkenyl iodides and chlorides was formed.
bearing feebly electron-withdrawing substituents (F & Br),
To inspect the versatility of the process, first,
were underwent smoothly to deliver the anticipated products
synthesized the secondary benzylic alcohols 1a-i according to
3df (78%, E:Z = 88:12) and 3dg (80%, E:Z = 89:11). However,
the previous literature reports[36-41] or commercially
arylacetylenes 2m and 2n bearing solid electron-withdrawing
purchased; subsequently, subjected them to the optimized
groups (NO2 & CN) could not promote the reaction, which
reaction conditions with the terminal acetylenes (Table 1,
would be obvious for such electrophilic substitution reactions.
Entry 6). Now, these alcohols 1a-i were treated with different
Notably, the reaction was also successful even with the
terminal alkynes 2a-h under established microwave heating
electron-rich aromatic acetylene 2l in delivering the
conditions (i.e., Table 1, entry 6). Remarkably, benzylic
corresponding alkenyl halide 3al; however, at a slightly low
alcohols containing both electron-donating and feebly
temperature (80 C, 20 min) than the usual conditions.
electron-deficient groups were reacted well and afforded the
Besides, it is worth mentioning that the major isomers of the
anticipated products 3aa-al in fair to very good yields (66 to
products 3ac-ae, 3al were separated from their minor ones
88%) with ample regioselectivity (Markovnikov product) and
during the column chromatography and hence isolated as
with tall E-selectivity (up to E:Z = 98:02), as presented in Table
single isomeric products.
2. Specifically, the products 3aa-ae from diphenylmethanol 1a
and arylacetylenes (2a, 2b, 2c & 2e) resulted in good to very
good yields (77 to 88%). Delightfully, alkyl aryl secondary
alcohols 1d-i have been well tolerated with a variety of
terminal alkynes 2a-n and furnished products 3aa-al in yields
ranging from 66 to 88%. Notably, the reaction was also
smooth between the secondary alcohol 1d the aliphatic
acetylene 2h; however, successful at slightly elevated 130 C
heating conditions (3dh; 69%). Particularly, arylacetylenes
Table 2: Scope of alkenyl iodides 3aa-al from benzylic alcohols 1a-i and terminal alkynes 2a-n.a,b,c,d
4
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aReaction condition: 1a-i (1 equiv, 0.5 mmol), 2a-h (1 equiv, 0.5 mmol), ZnI2 (1 equiv, 0.5 mmol), 1,2-DCE (1 mL) solvent under microwave
b
c
irradiation at 120 °C for 20 min (300, closed vessel). Isolated yields of products 3aa-al of E/Z mixture. The E/Z ratio was calculated by 1H
d
NMR analysis of the products containing non-separable E/Z mixture. Reaction was performed under microwave irradiation at 130 °C, for 20
min (300, closed vessel). eThe major isomer was separated from the minor one. fReaction was performed under microwave irradiation at 80 °C,
for 20 min (300, closed vessel). gNo product was formed.
alcohols are treated with simple phenylacetylene 2a gave the
corresponding alkenyl chlorides 4ba, 4da, and 4ea in high
yields (Table 3). Especially, the protocol was acquiescent with
1,2,3,4-tetrahydronaphthalen-1-ol 1c and phenylacetylene 2a
to give the anticipated alkenyl chloride 4ca in fair yield (60%).
Next, to explore the generality of Zn-halides, the
method was further investigated using ZnCl2 as the Lewis acid
and chlorinating agent. Thus, the biphenylcarbinol 1a is
reacted with phenylacetylenes (2a & 2b) under standard
conditions using microwave irradiation, as shown in Table 3.
As a result, the expected products were isolated in good yields
(4aa in 70% yield, with E/Z ratio of 89:11 & 4ac in 71%, with
E/Z ratio of 84:16). When biphenylcarbinol 1a, is treated with
aliphatic alkyne (1-heptyne 2h), under the standard reaction
conditions it resulted in only 34% yield, by TLC perceived that
still, both the starting materials are leftover. Therefore, the
reaction at a slightly elevated temperature (i.e., 130 C for 20
min), especially, with the less reactive aliphatic alkyne 2h
furnished the desired alkenyl chlorides 4ah with an improved
yield of 67% with E/Z ratio of 51:49. Further, 1-phenylethan-1-
ol 1b, and para-substituted methyl 1d and bromo 1e benzylic
Table 3: Scope of alkenyl chlorides 4aa-ea from 1a-e and
2a/2c/2h.a,b,c,d
5
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aReaction condition: 1a/1b/1d/1h (1 equiv, 0.5 mmol), 2a-e (1 equiv,
0.5 mmol), ZnBr2 (1 equiv, 0.5 mmol), 1,2-DCE (1 mL) solvent under
microwave irradiation at 120 °C for 20 min (300, closed vessel).
bIsolated yields of products 5ac-ha of E/Z mixture. cThe E:Z ratio
calculated by 1H NMR analysis of the products containing
nonseparable E/Z mixture. eThe major isomer was separated from the
minor one
aReaction condition: 1a-e (1 equiv, 0.5 mmol), 2a/2c/2h (1 equiv, 0.5
mmol), ZnCl2 (1 equiv, 0.5 mmol), 1,2-DCE (1 mL) solvent under
microwave irradiation at 120 °C for 20 min (300, closed vessel).
bIsolated yields of products 4aa-ea of E/Z mixture. cThe E:Z ratio
calculated by 1H NMR analysis of the products containing non-
separable E/Z mixture. dReaction was performed under microwave
irradiation at 130 °C (300, closed vessel).
Surprisingly, when tertiary alcohol 1j is treated with
aromatic acetylenes (2a, 2c, 2d & 2e) in the presence of ZnCl2
at 120 C for 20 min resulted in the unexpected cyclization
indene products (6ja, 6jc, 6jd & 6je) in decent yields (Table
5). Interestingly, the same indene products (6ja, 6jc, 6jd &
6je) were also obtained in comparable yields when ZnI2 was
used as the promoter under identical conditions and with the
same starting materials as depicted in Table 5.
Furthermore, we turned out attention to investigate
this protocol using ZnBr2 as the promoter as well as the
brominating agent. As expected, it was detected that ZnBr2
reacted proficiently under the optimized conditions upon
performing the reactions with various benzylic alcohols
1a/1b/1d/1h and terminal alkynes 2a-e and gave the
corresponding alkenyl bromides 5ac-ha (Table 4) in modest
to high yields (65 to 82%) and good selectivity (up to E:Z =
85:15) under the established conditions of microwave
acceleration. Thus, it is estimated that the present method is
quite general concerning benzylic alcohols and acetylenes. At
large, the reaction is fairly efficient, has high yields, and is
straightforward. These alkenyl halides 3aa-al, 4aa-ea, and
5ac-ha have been characterized by spectrometric techniques
(1H-NMR, 13C-NMR, and Mass Spectrometry).
Table 5: Access to indenes 6ja-je from 1j and 2a-e.a,b
aReaction condition: 1j (1 equiv, 0.5 mmol), 2a-e (1 equiv, 0.5 mmol),
ZnCl2/ZnI2 (1 equiv, 0.5 mmol), 1,2-DCE (1 mL) solvent under
microwave irradiation at 120 °C for 20 min (300, closed vessel).
bIsolated yields of products 6ja-je.
Table 4: Synthesis of alkenyl bromides 5ac-ha from 1a-h and 2a-
e.a,b,c
6
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aReaction condition: 1d-h (1 equiv, 0.5 mmol), 2k (1 equiv, 0.5 mmol),
ZnI2 (1 equiv, 0.5 mmol), 1,2-DCE (1 mL) solvent in microwave at
It is worth noting that when the reactions are
b
130 °C for 30 min (300, closed vessel). Isolated yields of products
performed, especially, with a strong electron-donating group
bearing aryl alkynes 2k, and 2l with benzylic alcohols 1a and
1d-h in the presence of ZnI2 under the standard conditions at
130 C, for 30 min, to our surprise, furnished the aryl ketones
7dk-al as exclusive products with yields ranging from 62 to
82% instead of affording the usual alkenyl iodides, as depicted
in Table 6. Whereas the usual conditions (i.e., 120 C, for 20
min) led to the mixture of iodoalkene and the ketone.
7dk-al.
A probable mechanism is proposed as shown in
Scheme 1. Firstly, benzylic alcohol 1 is activated by the Lewis
acid (ZnX2), leading to the formation of an activated complex
A, which further undergoes substitution by another molecule
benzylic alcohol 1, and readily gets converted into the
condensed ether 1a (it can be isolated) along with the
elimination of water. Yet again, the intermediate ether 1a
combines with the Lewis acid and results in oxonium
intermediate B. Now, the intermediate B proceeds through
nucleophilic attack by terminal alkyne 2 and furnishes vinyl
carbocation species C, which could combine with halide from
the in-situ generated HX or ZnX2 generating alkenyl halide
3/4/5 with outstanding regioselectivity (Markovnikov product)
and E-selectivity. In the case of tert-alcohols, the reaction with
arylacetylenes generated the vinyl carbocation intermediate C
which would undergo intramolecular cyclization competitively
and gives the indene products 6; this could be attributed to the
Thorpe–Ingold and electronic effects. Moreover, when an
electron-rich arylacetylene was employed, due to the
susceptible dipolar nature of intermediate or even the
corresponding alkenyl halide, it would undergo hydrolysis with
in-situ formed water leading to the formation of aryl ketones 7.
Table 6: Formation of ketones 7dk-al from 1d/1f/1g/1h and 2k/2l.a,b
7
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Scheme 1: Plausible mechanism for synthesis of alkenyl halides 3/4/5, indenes 6, and aryl ketones 7.
(central line of triplet)]. In the 1H-NMR, the following
abbreviations were used throughout: s = singlet, d = doublet,
t = triplet, dd = doublet of doublet, dq = doublet of quartet, m
Conclusion
In conclusion, a simple method (i.e., microwave-
1
= multiplet. The assignment of signals was confirmed by H,
accelerated synthesis, and by the use of single reagent to
avoid waste generation) for the effective synthesis for a wide
range of alkenyl halides via direct C–C bond formation and
halogenation sequence triggered by mild zinc-halides starting
from benzylic alcohols and terminal acetylenes is presented.
In comparison with other reported methods, this method would
be a convenient approach in achieving diversified halo-
alkenes (chloro-alkenes, fluoro-alkenes, and iodo alkenes).
Further, the synthesis of indenes was shown feasible by this
method based on the nature of starting materials. Also,
exemplified with the direct synthesis of ketones, particularly,
when sufficiently electron-rich arylacetylenes were used.
13C, and DEPT spectra. High-resolution mass spectra (HR-
MS) were recorded on an Agilent 6538 UHD Q-TOF electron
spray ionization (ESI) mode. The microwave irradiation
experiments were carried out in a dedicated CEMD is cover
monomode microwave apparatus, operating at a frequency of
2.45 GHz with continuous irradiation power from 0 to 300 W
and utilization of the standard absorbance level of 100 W. The
reactions were carried out in 10 mL glass tubes, sealed with
Teflon septum, and placed in the microwave cavity. The
reactions were irradiated at the required set temperature for
the stipulated time and then cooled to ambient temperature
with air-jet cooling. Reactions were monitored by TLC on silica
gel using a combination of hexane and ethyl acetate as
eluents. Reactions were generally run under argon or a
nitrogen atmosphere.
Experimental Section
General: IR spectra were recorded on a Bruker Tensor 37
(FTIR) spectrophotometer. 1H NMR spectra were recorded on
Bruker Avance 400 (400 MHz) spectrometer at 295 K in
CDCl3; chemical shifts (δ ppm) and coupling constants (J) are
reported in standard fashion with reference to either internal
standard tetramethylsilane (TMS) (δH = 0.00 ppm) or CHCl3
(δH = 7.25 ppm). 13C NMR spectra were recorded on Bruker
Avance 400 (100 MHz) spectrometer at RT in CDCl3; chemical
shifts (δ ppm) are reported relative to CHCl3 [δC = 77.00 ppm
Solvents and chemicals:
Solvents were distilled before use; petroleum ether
with a boiling range of 60 to 80 °C was used. The Lewis acids
ZnCl2, ZnBr2, and ZnI2 were purchased from Sigma-Aldrich
and used as received. Terminal alkynes were purchased from
Sigma-Aldrich/TCI/local sources and used as received.
Acme’s silica gel (60–120 mesh) was used for column
8
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(E)-(3-(4-Ethylphenyl)-3-iodoprop-2-ene-1,1-
chromatography (approximately 20 g per one gram of crude
material).
diyl)dibenzene (3ad):
GP-1 (General procedure for the synthesis of alkenyl
halides): To an oven-dried 10 mL glass tube sealed with
Teflon septum, and equipped with a magnetic stir bar, were
GP-1 was carried out with diphenylmethanol 1a (91 mg, 0.5
mmol) and 1-ethyl-4-ethynylbenzene 2d (65 mg, 0.5 mmol),
ZnI2 (160 mg, 0.5 mmol) and DCE (2 mL). Purification of the
crude mixture by silica gel column chromatography (petroleum
ether/ethyl acetate 100:0 to 99:1), furnished the alkenyl iodide
3ad as a transparent liquid (172 mg, 81%). [TLC control
(petroleum ether/ethyl acetate 100:0), Rf(3ad) = 0.7, UV
detection]. IR (MIR-ATR, 4000–600 cm-1): max = 3020, 2966,
1596, 1489, 1446, 732, 751, 835, 593 cm-1. 1H NMR (400 MHz,
CDCl3) δ = 7.33 – 7.27 (m, 4H), 7.26 – 7.17 (m, 4H), 7.16 –
7.08 (m, 6H), 6.91 (d, J = 10.7 Hz, 1H), 4.69 (d, J = 10.7 Hz,
1H), 2.64 (q, J = 7.6 Hz, 2H), 1.25 (t, J = 7.6 Hz, 3H) ppm.
13C{1H} NMR (100 MHz, CDCl3) δ = 144.5, 143.7, 142.9, 138.7,
128.6, 128.4, 128.2, 127.8, 126.5, 96.4, 52.6, 28.6, 15.2 ppm.
HR-MS (ESI+) m/z calculated for [C23H21KI]+ = [M+K]+:
463.0320; found 463.0330.
added benzylic alcohols 1a-i
(61-100 mg, 0.5 mmol),
terminal alkynes 2a-h (51-90 mg, 0.5 mmol), followed by the
addition of ZnX2 (0.5 mmol) and DCE as solvent (2 mL). The
resultant reaction mixture was irradiated under microwave
irradiation at 120 °C for 20 min and brought to ambient
temperature (In the case of aliphatic terminal alkyne as the
starting material, the reaction has performed at 130 C for 20
min). The progress of the reaction was monitored by TLC till
the reaction is completed. The reaction mixture was washed
with saturated NH4Cl solution and extracted by using ethyl
acetate (3  20 mL). The combined organic layers were
washed with brine (NaCl) solution, dried (Na2SO4),and filtered.
Evaporation of the solvent(s) under reduced pressure and
purification of the crude mixture by silica gel column
chromatography (petroleum ether/ethyl acetate), furnished
the alkenyl iodide 3aa-al (66-88%), the alkenyl chloride 4aa-
ea (60-80%), and the alkenyl bromide 5ac-ha (65-82%) as a
mixture of E (major) and Z (minor) isomers as liquid, and the
indenes 6ja-je (75-89%).
(E)-(3-(4-Butylphenyl)-3-iodoprop-2-ene-1,1-
diyl)dibenzene (3ae):
GP-1 was carried out with diphenylmethanol 1a (91 mg, 0.5
mmol) and 1-butyl-4-ethynylbenzene 2e (79 mg, 0.5 mmol),
ZnI2 (160 mg, 0.5 mmol) and DCE (2 mL). Purification of the
crude mixture by silica gel column chromatography (petroleum
ether/ethyl acetate 100:0 to 99:1), furnished the alkenyl iodide
3ae as colorless liquid (174 mg, 77%). [TLC control
(petroleum ether/ethyl acetate 100:0), Rf(3ae) = 0.7, UV
detection]. IR (MIR-ATR, 4000–600 cm-1): max = 3023, 2954,
GP-2 (General procedure for the synthesis of aryl
ketones): To an oven-dried 10 mL glass tube sealed with
Teflon septum, and equipped with a magnetic stir bar, were
added benzylic alcohols 1a & 1d-h (68-92 mg, 0.5 mmol),
terminal alkynes 2k, 2l & 2m (66-96 mg, 0.5 mmol), followed
by the addition of ZnI2 (160 mg, 0.5 mmol) and solvent DCE
(2 mL). The resultant reaction mixture was irradiated under
microwave irradiation at 130 °C for 20 min and brought to
ambient temperature. Progress of the reaction was monitored
by TLC till the reaction is completed. The reaction mixture was
washed with saturated NH4Cl solution and extracted by using
ethyl acetate (3  20 mL). The combined organic layers were
washed with brine (NaCl) solution, dried (Na2SO4),and filtered.
Evaporation of the solvent(s) under reduced pressure and
purification of the crude mixture by silica gel column
chromatography (petroleum ether/ethyl acetate), furnished
the aryl ketones 7dk-al (62-82%) as a liquid.
1
2927, 1598, 1452, 1492, 739, 698 cm-1. H NMR (400 MHz,
CDCl3) δ = 7.34 – 7.26 (m, 4H), 7.26 – 7.16 (m, 4H), 7.13 –
7.08 (m, 6H), 6.91 (d, J = 10.7 Hz, 1H), 4.69 (d, J = 10.7 Hz,
1H), 2.93 – 2.25 (m, 2H), 1.65 – 1.56 (m, 2H), 1.39 – 1.34 (m,
2H), 0.93 (t, J = 7.3 Hz, 3H) ppm. 13C{1H} NMR (100 MHz,
CDCl3) δ = 143.6, 143.3, 142.9, 138.6, 128.6, 128.4, 128.3,
128.2, 126.5, 96.5, 52.6, 35.4, 33.4, 22.4, 14.0 ppm. HR-MS
(ESI+) m/z calculated for [C25H25KI]+ = [M+K]+: 491.0633;
found 491.0622.
1-Bromo-4-(4-iodo-4-phenylbut-3-en-2-yl)benzene (3ea):
GP-1 was carried out with 1-(4-bromophenyl)ethan-1-ol 1e
(100 mg, 0.5 mmol) and ethynylbenzene 2a (51 mg, 0.5
mmol), ZnI2 (160 mg, 0.5 mmol) and DCE (2 mL). Purification
of the crude mixture by silica gel column chromatography
(petroleum ether/ethyl acetate 100:0 to 99:1), furnished the
9
This article is protected by copyright. All rights reserved.

10.1002/ejoc.202100779
European Journal of Organic Chemistry
FULL PAPER
alkenyl iodide 3ea as a transparent liquid (159 mg, 77%). [TLC
control (petroleum ether/ethyl acetate 100:0), Rf(3ea) = 0.7,
UV detection]. IR (MIR-ATR, 4000–600 cm-1): max= 3740,
3648, 3614, 3560, 3446, 3022, 2961, 2920, 2854, 2370, 2315,
2198, 2142, 1990, 1871, 1838, 1749, 1695, 1498, 1463, 1422,
3ga as mixture of E and Z isomers as yellow jelly (138 mg,
75%, E:Z = 82:18). [TLC control (petroleum ether/ethyl
acetate 100:0), Rf(3ga) = 0.8, UV detection]. IR (MIR-ATR,
4000–600 cm-1): max= 3743, 3675, 3562, 3055, 2965, 2923,
2861, 2367, 2315, 1995, 1874, 1833, 1741, 1694, 1648, 1489,
1454, 1401, 1275, 1179, 1111, 1072, 1007, 918, 870, 824,
762 cm-1. 1H NMR (CDCl3, 400 MHz, major isomer): δ = 7.43
– 7.03 (m, 9H), 6.55 (d, J = 12 Hz, 1H), 3.47 – 3.39 (m, 1H),
1.29 (d, J = 6.8 Hz, 3H) ppm. 13C{1H} NMR (CDCl3, 100 MHz,
major isomer): δ = 146.4, 142.8, 142.3, 141.6, 132.1, 128.7,
128.6, 128.6, 128.5, 128.3, 128.2, 128.1, 94.7, 41.3, 21.6 ppm.
HR-MS (ESI+) m/z calculated for [C16H14Cl]+=[MI]+:
241.0790; found 241.0796.
1
1252, 1166, 1091, 1010, 882, 829 cm-1. H NMR (400 MHz,
CDCl3, major isomer) δ = 7.46 – 7.38 (m, 3H), 7.35 – 7.22 (m,
6H), 6.99 (d, J = 8.4 Hz, 2H), 6.55 (d, J = 10.4 Hz, 1H), 3.42
(dq, J = 10.5, 6.9 Hz, 1H), 1.29 (d, J = 7.0 Hz, 3H) ppm. 13
C
NMR (100 MHz, CDCl3) δ = 146.4, 143.4, 141.7, 131.7, 128.5,
128.3, 128.2, 120.1, 94.7, 41.4, 21.5 ppm. HR-MS (ESI+) m/z
calculated for [C16H14Br79INa]+ = [M+Na]+: 434.9216; found
434.9235. HR-MS (ESI+) m/z calculated for [C16H14Br81INa]+
= [M+Na]+: 436.9195; found 436.9165.
(1-Iodopent-1-ene-1,3-diyl)dibenzene(3ha):
1-Fluoro-4-(4-iodo-4-phenylbut-3-en-2-yl)-2-
GP-1 was carried out with 1-phenylpropan-1-ol 1h (68 mg, 0.5
mmol) and ethynylbenzene 2a (51 mg, 0.5 mmol), ZnI2 (160
mg, 0.5 mmol) and DCE (2 mL). Purification of the crude
mixture by silica gel column chromatography (petroleum
ether/ethyl acetate 100:0 to 99:1), furnished the alkenyl iodide
3ha as a transparent liquid (135 mg, 78%). [TLC control
(petroleum ether/ethyl acetate 100:0), Rf(3ha) = 0.7, UV
detection]. IR (MIR-ATR, 4000–600 cm-1): max = 3024, 2968,
1597, 1499, 1443, 737, 746, 831, 599 cm-1. 1H NMR (400 MHz,
CDCl3, major isomer) δ = 7.32 – 7.26 (m, 5H), 7.24 – 7.20 (m,
3H), 7.11 – 7.06 (m, 2H), 6.59 (d, J = 10.7 Hz, 1H), 3.15 (dt, J
= 10.7, 7.4 Hz, 1H), 1.73 – 1.60 (m, 2H), 0.79 (t, J = 7.4 Hz,
3H) ppm. 13C NMR (100 MHz, CDCl3) δ = 146.2, 143.4, 142.0,
128.6, 128.5, 128.2, 128.0, 127.2, 126.4, 94.7, 49.6, 29.4,
11.9 ppm. HR-MS (ESI+) m/z calculated for [C17H17INa]+ =
[M+Na]+: 371.0267; found 371.0313.
methylbenzene(3fa):
GP-1 was carried out with 1-(4-fluoro-3-methylphenyl)ethan-
1-ol 1f (100 mg, 0.5 mmol) and ethynylbenzene 2a (51 mg,
0.5 mmol), ZnI2 (160 mg, 0.5 mmol) and DCE (2 mL).
Purification of the crude mixture by silica gel column
chromatography (petroleum ether/ethyl acetate 100:0 to
99:1), furnished the alkenyl iodide 3fa as a transparent liquid
(130 mg, 71%). [TLC control (petroleum ether/ethyl acetate
100:0), Rf(3fa) = 0.7, UV detection]. IR (MIR-ATR, 4000–600
cm-1): max= 3744, 3670, 3612, 3020, 2932, 2864, 2311, 2199,
2149, 1735, 1690, 1653, 1506, 1450, 1269, 1120, 1070, 1029,
1
887, 731 cm-1. H NMR (400 MHz, CDCl3, E & Z-isomer) δ =
7.37 – 7.30 (m, 2H), 7.29 – 7.24 (m, 3H), 6.93 – 6.88 (m, 3H),
6.56 (d, J = 10.5 Hz, 1H), 5.93 (d, J = 9.0 Hz, 0.2H), 3.85 (dd,
J = 8.8, 7.0 Hz, 0.19H), 3.40 (dq, J = 10.5, 7.0 Hz, 1H), 2.25
(d, J = 2.0 Hz, 3H), 1.28 (d, J = 7.0 Hz, 3H) ppm. 13C NMR
(100 MHz, CDCl3) δ = 161.1, 158.7, 147.1, 142.9, 141.8,
139.8, 139.8, 130.0, 129.7, 129.6, 128.7, 128.3, 128.3, 128.2,
125.8, 125.4, 125.4, 124.9, 115.1, 114.9, 94.2, 41.2, 21.8,
14.7, 14.6 ppm. HR-MS (ESI+) m/z calculated for
[C17H16FINa]+ = [M+Na]+: 389.0173; found 389.0117.
1-(4-Iodo-4-phenylbut-3-en-2-yl)-4-methoxybenzene(3ia):
GP-1 was carried out with 1-(4-methoxyphenyl)ethan-1-ol 1i
(76 mg, 0.5 mmol) and ethynylbenzene 2a (51 mg, 0.5 mmol),
ZnI2 (160 mg, 0.5 mmol) and DCE (2 mL). Purification of the
crude mixture by silica gel column chromatography (petroleum
ether/ethyl acetate 100:0 to 99:1), furnished the alkenyl iodide
3ia as a transparent liquid (120 mg, 66%). [TLC control
(petroleum ether/ethyl acetate 100:0), Rf(3ia) = 0.7, UV
detection]. IR (MIR-ATR, 4000–600 cm-1): max= 3732, 3670,
3612, 3050, 2961, 2924, 2853, 2310, 2191, 2137, 1989, 1842,
1740, 1692, 1649, 1514, 1452, 1261, 1110, 1019, 894, 819
cm-1. 1H NMR (400 MHz, CDCl3, major isomer) δ = 7.32 – 7.25
1-Chloro-4-(4-iodo-4-phenylbut-3-en-2-yl)benzene (3ga):
GP-1 was carried out with 1-(4-chlorophenyl)ethanol 1g (79
mg, 0.5 mmol) and ethynylbenzene 2a (51 mg, 0.5 mmol), ZnI2
(160 mg, 0.5 mmol) and DCE (2 mL). Purification of the crude
mixture by silica gel column chromatography (petroleum
ether/ethyl acetate 100:0 to 99:1), furnished the alkenyl iodide
10
This article is protected by copyright. All rights reserved.

10.1002/ejoc.202100779
European Journal of Organic Chemistry
FULL PAPER
(m, 5H), 7.06 – 7.02 (m, 2H), 6.85 – 6.80 (m, 2H), 6.56 (d,
J=10.5, 1H), 3.76 (s, 3H), 3.41 (dq, J=10.5, 6.9, 1H), 1.28 (d,
J=7.0, 3H) ppm. 13C NMR (100 MHz, CDCl3) δ = 158.0, 147.5,
141.8, 136.4, 128.4, 128.2, 128.1, 127.6, 114.0, 93.8, 55.2,
41.0, 21.7 ppm. HR-MS (ESI+) m/z calculated for
[C17H18IO]+=[M+H]+: 365.0397; found 365.0397.
1H), 2.30 (s, 3H), 1.28 (d, J = 6.9 Hz, 3H) ppm. 13C{1H} NMR
(CDCl3, 100 MHz, major isomer): δ = 162.2 (1Jc-f = 246 Hz),
148.1, 144.2, 143.8, 143.8, 141.0, 136.0, 129.8 (3Jc-f = 8 Hz),
129.3, 129.3, 126.9, 126.6, 124.1 (4Jc-f = 3 Hz), 115.5 (2Jc-f
=
22 Hz), 115.1 (2Jc-f = 21 Hz), 91.5, 41.6, 21.6, 20.9 ppm. HR-
MS (ESI+) m/z calculated for [C17H16FINa]+=[M+Na]+:
389.0173; found 389.0117.
1-(4-Iodonon-3-en-2-yl)-4-methylbenzene (3dh):
GP-1 was carried out with 1-(p-tolyl)ethanol 1d (68 mg, 0.5
mmol) and 1-ethynyl-3-fluorobenzene 2h (48 mg, 0.5 mmol),
ZnI2 (160 mg, 0.5 mmol) and DCE (2 mL). Purification of the
crude mixture by silica gel column chromatography (petroleum
ether/ethyl acetate 100:0 to 99:1), furnished the alkenyl iodide
3dh as mixture of E and Z isomers as colorless liquid (118 mg,
69%, E:Z = 53:47). [TLC control (petroleum ether/ethyl
acetate 100:0), Rf(3dh) = 0.8, UV detection]. IR (MIR-ATR,
4000–600 cm-1): max= 3742, 3647, 3616, 3564, 3447, 3027,
2963, 2923, 2856, 2369, 2314, 2196, 2144, 1992, 1870, 1834,
1741, 1690, 1648, 1498, 1459, 1419, 1262, 1169, 1095, 1011,
885, 822, 740 cm-1. 1H NMR (CDCl3, 400 MHz, E & Z-isomer)
δ = 7.19 – 7.09 (m, 8H), 6.30 (d, J = 9.8 Hz, 1H), 5.54 (d, J =
8.9 Hz, 1H), 3.75 – 3.57 (m, 2H), 2.49 – 2.40 (m, 4H), 2.32 (s,
6H), 1.55 – 1.48 (m, 4H), 1.36 – 1.26 (m, 14H), 0.88 (dd, J =
7.1 and 3.7 Hz, 6H) ppm. 13C{1H} NMR (CDCl3, 100 MHz, E &
Z-isomer): δ = 145.6, 141.8, 139.3, 135.8, 129.2, 129.1, 128.3,
127.2, 126.8, 126.6, 108.3, 103.4, 46.0, 45.0, 40.5, 38.7, 30.6,
30.6, 29.0, 28.9, 22.5, 22.3, 22.0, 21.0, 20.5, 14.0 ppm. HR-
MS (ESI+) m/z calculated for [C16H24I]+=[M+H]+: 343.0917;
found 343.1018.
(3-Iodo-3-(3,4,5-trimethoxyphenyl)prop-2-ene-1,1-
diyl)dibenzene (3al): GP-1 was carried out with
diphenylmethanol 1a (92 mg, 0.5 mmol) and 5-ethynyl-1,2,3-
trimethoxybenzene 2l (96 mg, 0.5 mmol), ZnI2 (160 mg, 0.5
mmol) and DCE (2 mL). Purification of the crude mixture by
silica gel column chromatography (petroleum ether/ethyl
acetate 100:0 to 90:10), furnished the alkenyl iodide 3al as
mixture of E and Z isomers as yellow liquid (187 mg, 77%, E:Z
97:03). [TLC control (petroleum ether/ethyl acetate 85:15),
Rf(3al) = 0.6, UV detection]. IR (MIR-ATR, 4000–600 cm-1):

max= 3752, 3680, 3616, 3032, 2930, 2866, 2318, 2186, 2133,
1731, 1695, 1658, 1506, 1457, 1268, 1112, 1076, 1023, 891,
745 cm-1. 1H NMR (400 MHz, CDCl3, major isomer) δ = 7.33 –
7.31(m, 4H), 7.30 – 7.21 (m, 6H), 6.71 (s, 2H), 6.33 (dd, J=9.3,
1.0, 1H), 5.16 (d, J=9.2, 1H), 3.86 (s, 6H), 3.84 (s, 3H) ppm.
13C NMR (100 MHz, CDCl3) δ = 152.5, 142.4, 139.8, 138.7,
138.3, 128.6, 128.3, 126.7, 106.1, 106.1, 60.9, 58.7, 56.2 ppm.
HR-MS (ESI+) m/z calculated for [C24H24IO3]+=[M+H]+:
487.0765; found 487.0775.
(3-Chlorooct-2-ene-1,1-diyl)dibenzene (4ah):
GP-1 was carried out with diphenylmethanol 1a (92 mg, 0.5
mmol) and hept-1-yne 2h (48 mg, 0.5 mmol), ZnCl2 (68 mg,
0.5 mmol) and DCE (2 mL). Purification of the crude mixture
by silica gel column chromatography (petroleum ether/ethyl
acetate 100:0 to 99:1), furnished the alkenyl iodide 4ah as
mixture of E and Z isomers as yellow liquid (100 mg, 67%, E:Z
51:49). [TLC control (petroleum ether/ethyl acetate 100:0),
Rf(4ah) = 0.8, UV detection]. IR (MIR-ATR, 4000–600 cm-1):
1-Fluoro-3-(1-iodo-3-(p-tolyl)but-1-en-1-yl)benzene (3df):
GP-1 was carried out with 1-(p-tolyl)ethanol 1d (68 mg, 0.5
mmol) and 1-ethynyl-3-fluorobenzene 2f (60 mg, 0.5 mmol),
ZnI2 (160 mg, 0.5 mmol) and DCE (2 mL). Purification of the
crude mixture by silica gel column chromatography (petroleum
ether/ethyl acetate 100:0 to 99:1), furnished the alkenyl iodide
3df as mixture of E and Z isomers as colorless liquid (142 mg,
78%, E:Z = 88:12). [TLC control (petroleum ether/ethyl
acetate 100:0), Rf(3df) = 0.8, UV detection]. IR (MIR-ATR,
4000–600 cm-1): max= 3742, 3675, 3615, 3020, 2966, 2923,
2867, 2365, 2315, 2197, 2147, 1999, 1834, 1741, 1694, 1648,
1572, 1515, 1433, 1261, 1234, 1136, 1014, 949, 884, 812,
774, 701 cm-1. 1H NMR (CDCl3, 400 MHz, major isomer): δ =
7.43  7.01 (m, 9H), 6.59 (d, J = 12 Hz, 1H), 3.47 – 3.39 (m,

max= 3742, 3675, 3615, 3028, 2929, 2861, 2315, 2196, 2139,
1739, 1694, 1650, 1502, 1455, 1264, 1118, 1071, 1029, 893,
735 cm-1. 1H NMR (CDCl3, 400 MHz, E & Z-isomer): δ = 7.31
– 7.26 (m, 9H), 7.23 – 7.15 (m, 11H), 6.09 (d, J = 12 Hz, 1H),
5.95 (d, J = 12 Hz, 1H), 5.22 (d, J = 9.5 Hz, 1H), 4.86 (d, J =
10.2 Hz, 1H), 2.49 – 2.32 (m, 4H), 1.61 – 1.51 (m, 4H), 1.31 –
1.23 (m, 8H), 0.89 – 0.82 (m, 6H) ppm. 13C{1H} NMR (CDCl3,
11
This article is protected by copyright. All rights reserved.

10.1002/ejoc.202100779
European Journal of Organic Chemistry
FULL PAPER
100 MHz, E & Z-isomer): δ = 143.5, 143.4, 135.5, 129.9, 128.6, GP-1 was carried out with triphenylmethanol 1j (130 mg, 0.5
mmol) and 1-ethyl-4-ethynylbenzene 2d (65 mg, 0.5 mmol),
ZnI2 (160 mg, 0.5 mmol) and DCE (2 mL). Purification of the
crude mixture by silica gel column chromatography (petroleum
ether/ethyl acetate 100:0 to 99:1), furnished the triphenyl
indene 6jd as colorless liquid (165 mg, 89%). [TLC control
(petroleum ether/ethyl acetate 100:0), Rf(6jd) = 0.6, UV
detection]. IR (MIR-ATR, 4000–600 cm-1): max= 3742, 3677,
3616, 3053, 2963, 2923, 2857, 2312, 2195, 2133, 1997, 1833,
1741, 1695, 1647, 1514, 1456, 1263, 1113, 1014, 896, 815
cm-1. 1H NMR (400 MHz, CDCl3) δ = 7.57 (d, J = 8.1 Hz, 3H),
7.39 (d, J = 7.3 Hz, 1H), 7.32 – 7.19 (m, 14H), 6.79 (s, 1H),
2.70 (q, J = 7.6 Hz, 2H), 1.27 (t, J = 7.6 Hz, 3H) ppm. 13C{1H}
NMR (100 MHz, CDCl3) δ = 151.1, 144.1, 143.8, 142.3, 141.1,
132.6, 129.2, 128.3, 128.1, 127.9, 127.7, 126.9, 126.6, 125.7,
125.6, 121.4, 65.5, 28.7, 15.6 ppm. HR-MS (ESI+) m/z
calculated for [C29H25]+=[M+H]+: 373.1951; found 373.1947.
128.5, 128.4, 128.2, 128.2, 128.1, 127.4, 126.5, 126.4, 49.8,
39.5, 33.9, 31.0, 27.0, 26.1, 22.4, 13.9 ppm. HR-MS (ESI+)
m/z calculated for [C20H23Cl]+=[M]+: 298.1488; found
298.1674.
(Z)-(3-Bromo-3-(4-ethylphenyl)prop-2-ene-1,1-
diyl)dibenzene (5ad):
GP-1 was carried out with diphenylmethanol 1a (91 mg, 0.5
mmol) and 1-ethyl-4-ethynylbenzene 2d (65 mg, 0.5 mmol),
ZnBr2 (112 mg, 0.5 mmol) and DCE (2 mL). Purification of the
crude mixture by silica gel column chromatography (petroleum
ether/ethyl acetate 100:0 to 99:1), furnished the alkenyl
bromide 5ad as colorless liquid (141 mg, 75%). [TLC control
(petroleum ether/ethyl acetate 100:0), Rf(5ad) = 0.7, UV
detection]. IR (MIR-ATR, 4000–600 cm-1): max= 3056, 3020,
1
2963, 1596, 1489, 1444, 1459, 821, 760, 690 cm-1. H NMR
(400 MHz, CDCl3) δ = 7.32 – 7.25 (m, 4H), 7.25 – 7.19 (m,
4H), 7.19 – 7.09 (m, 6H), 6.64 (d, J = 10.9 Hz, 1H), 4.73 (d, J
= 10.9 Hz, 1H), 2.66 (q, J = 7.6 Hz, 2H), 1.24 (t, J = 7.6 Hz,
3H) ppm. 13C{1H} NMR (100 MHz, CDCl3) δ = 145.0, 143.1,
135.6, 135.1, 128.7, 128.6, 128.3, 128.2, 127.8, 127.7, 126.6,
121.6, 51.6, 28.6, 15.3 ppm.
3-(4-Butylphenyl)-1,1-diphenyl-1H-indene (6je):
GP-1 was carried out with triphenylmethanol 1j (130 mg, 0.5
mmol) and 1-butyl-4-ethynylbenzene 2e (79 mg, 0.5 mmol),
ZnI2 (160 mg, 0.5 mmol) and DCE (2 mL). Purification of the
crude mixture by silica gel column chromatography (petroleum
ether/ethyl acetate 100:0 to 99:1), furnished the triphenyl
indene 6je as colorless liquid (176 mg, 88%). [TLC control
(petroleum ether/ethyl acetate 100:0), Rf(6je) = 0.6, UV
detection]. IR (MIR-ATR, 4000–600 cm-1): max= 3742, 3677,
3616, 3053, 2963, 2923, 2857, 2312, 2195, 2133, 1997, 1833,
1741, 1695, 1647, 1514, 1456, 1263, 1113, 1014, 896, 815
cm-1. 1H NMR (400 MHz, CDCl3) δ = 7.67 – 7.53 (m, 3H), 7.49
– 7.34 (m, 1H), 7.34 – 7.16 (m, 14H), 6.78 (d, J = 12.8 Hz, 1H),
2.74 – 2.51 (m, 2H), 1.73 – 1.54 (m, 2H), 1.43 – 1.34 (m, 2H),
0.95 (t, J = 7.3 Hz, 3H) ppm. 13C{1H} NMR (100 MHz, CDCl3)
δ = 151.1, 143.8, 142.7, 142.6, 142.3, 141.1, 132.5, 128.6,
128.3, 127.8, 127.6, 126.9, 126.6, 125.7, 125.6, 121.4, 65.5,
35.5, 33.6, 22.4, 13.9 ppm. HR-MS (ESI+) m/z calculated for
[C31H29]+=[M+H]+: 401.2264; found 401.2234.
(Z)-(3-bromo-3-(4-butylphenyl)prop-2-ene-1,1-
diyl)dibenzene (5ae):
GP-1 was carried out with diphenylmethanol 1a (91 mg, 0.5
mmol) and 1-butyl-4-ethynylbenzene 2e (79 mg, 0.5 mmol),
ZnBr2 (112 mg, 0.5 mmol) and DCE (2 mL). Purification of the
crude mixture by silica gel column chromatography (petroleum
ether/ethyl acetate 100:0 to 99:1), furnished the alkenyl
bromide 5ae as colorless liquid (166 mg, 82%). [TLC control
(petroleum ether/ethyl acetate 100:0), Rf(5ae) = 0.7, UV
detection]. IR (MIR-ATR, 4000–600 cm-1): max= 3025, 2955,
2928, 1597, 1453, 1492, 737, 699 cm-1. 1H NMR (400 MHz,
CDCl3) δ = 7.33 – 7.26 (m, 4H), 7.23 (dt, J = 7.5, 5.7 Hz, 4H),
7.18 – 7.09 (m, 6H), 6.74 – 6.55 (m, 1H), 4.74 (d, J = 10.9 Hz,
1H), 2.65 – 2.55 (m, 2H), 1.64 – 1.56 (m, 2H), 1.43 – 1.30 (m,
2H), 0.93 (t, J = 7.3 Hz, 3H) ppm. 13C{1H} NMR (100 MHz,
CDCl3) δ = 143.7, 143.1, 135.5, 135.1, 128.7, 128.6, 128.3,
128.2, 127.6, 126.6, 121.6, 51.5, 35.4, 33.4, 22.4, 13.9 ppm.
3-(4-Fluoro-3-methylphenyl)-1-(4-methoxyphenyl)butan-
1-one (7fk):
GP-2 was carried out with 1-(4-methylphenyl)ethanol 1f (69
mg, 0.5 mmol) and 1-ethynyl-4-methoxybenzene 2k (51 mg,
0.5 mmol), ZnI2 (160 mg, 0.5 mmol) and DCE (2 mL).
Purification of the crude mixture by silica gel column
3-(4-Ethylphenyl)-1,1-diphenyl-1H-indene (6jd):
12
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10.1002/ejoc.202100779
European Journal of Organic Chemistry
FULL PAPER
chromatography (petroleum ether/ethyl acetate 100:0 to
95:05), furnished the aryl ketone 7fk as brown jelly (112 mg,
79%). [TLC control (petroleum ether/ethyl acetate 95:05),
Rf(7fk) = 0.5, UV detection]. IR (MIR-ATR, 4000–600 cm-1):
mmol), ZnI2 (160 mg, 0.5 mmol) and DCE (2 mL). Purification
of the crude mixture by silica gel column chromatography
(petroleum ether/ethyl acetate 100:0 to 85:15), furnished the
aryl ketone 7al as brown jelly (124 mg, 66%). [TLC control
(petroleum ether/ethyl acetate 95:05), Rf(7al)=0.5, UV
detection]. IR (MIR-ATR, 4000–600 cm-1): max= 3737, 3673,
3614, 2961, 2925, 2317, 1743, 1673, 1592, 1510, 1462, 1415,
1367, 1311, 1258, 1179, 1108, 1025, 987, 894, 832 cm-1. 1H
NMR (400 MHz, CDCl3) δ = 7.31 – 7.26 (m, 8H), 7.23 – 7.17
(m, 2H), 7.17 (s, 2H), 4.82 (t, J=7.3, 1H), 3.90 (s, 3H), 3.88 (s,
6H), 3.70 (d, J=7.3, 2H) ppm. 13C NMR (100 MHz, CDCl3) δ =
196.8, 153.0, 144.0, 142.5, 132.3, 128.6, 127.8, 126.4, 105.5,
60.9, 56.3, 46.1, 44.5 ppm.

max= 3743, 3677, 3648, 3616, 2960, 2924, 2853, 2369, 2316,
2057, 1996, 1833, 1740, 1675, 1600, 1505, 1459, 1420, 1361,
1306, 1254, 1172, 1118, 1030, 993, 934, 886, 823, 761 cm-1.
1H NMR (CDCl3, 400 MHz): δ = 7.91 (d, J = 8.8 Hz, 2H), 6.98
– 7.09 (m, 2H), 6.92 – 6.88 (m, 3H), 3.86 (s, 3H), 3.37 – 3.49
(m, 1H), 3.19 (dd, J = 16.4 and 6.1 Hz, 1H), 3.07 (dd, J = 16.4
and 6.1 Hz, 1H), 2.24 (d, J = 1.9 Hz, 3H), 1.29 (d, J = 6.8 Hz,
3H) ppm. 13C{1H} NMR (CDCl3, 100 MHz): δ = 197.5, 163.4,
159.8 (1Jc-f = 242 Hz), 158.6, 142.0, 142.0, 130.3, 130.2, 129.8
(3Jc-f = 5 Hz), 125.3 (3Jc-f = 8 Hz), 124.5 (2Jc-f = 17 Hz), 114.8
(2Jc-f = 21 Hz), 113.6, 55.4, 46.7, 35.0, 22.1, 14.6 ppm. HR-
MS (ESI+) m/z calculated for [C18H20FO2]+=[M+H]+: 287.1442;
found 287.1441.
Acknowledgments:
We are grateful to the Department of Science and Technology
Science and Engineering Research Board (DST-SERB) [No.
EMR/2017/005312], New Delhi, for financial support. K. G &
C. B. S thank UGC for the award of the research fellowship.
3-(4-Isopropylphenyl)-1-(4-methoxyphenyl)butan-1-one
(7kk):
GP-2 was carried out with 1-(4-isopropylphenyl)ethanol 1k (82
mg, 0.5 mmol) and 1-ethynyl-4-methoxybenzene 2k (66 mg,
0.5 mmol), ZnI2 (160 mg, 0.5 mmol) and DCE (2 mL).
Purification of the crude mixture by silica gel column
chromatography (petroleum ether/ethyl acetate 100:0 to
95:05), furnished the aryl ketone 7kk as brown jelly (121 mg,
82%). [TLC control (petroleum ether/ethyl acetate 95:05),
Rf(7kk)=0.5, UV detection]. IR (MIR-ATR, 4000–600 cm-1):
Keywords: Alkenyl halides, Halogenation, Lewis acids,
Microwave-assisted, Terminal acetylenes.
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Entry for the Table of Contents
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A simple Lewis acid-mediated route for the synthesis of alkenyl halides is described under microwave-assisted conditions. The reaction
proceeds through the condensation between sec-alcohols and terminal acetylenes, and regeoselective hydro halogenation across the
triple bond in the presence of simple and commercially available zinc halides. Unlike earlier reports, this methodology is successfully
exemplified with three halide sources. As a result, a diverse range of alkenyl halide products has been accomplished. Further, indenes
were obtained as the end products when tert-alcohols and aryl acetylenes were used, wherein, the Thorpe–Ingold, as well as electronic
effects, would be dominant. Furthermore, when an electron-rich aryl acetylene was employed, directed to yield carbonyl products.
15
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